Biology subjects

Miller, R. E.

Publications and source records attributed to Miller, R. E..

18 recordsLinked to original sources

bioRxiv2026

Integrated transcriptomic and epigenomic profiling of human cartilage reveals coordinated changes in fibronectin expression, splicing, and receptor signaling during osteoarthritis progression

Osteoarthritis (OA) is defined by progressive loss of articular cartilage, but how chondrocytes change as the disease advances is unclear because most studies have focused on end-stage tissue. We profiled human knee articular cartilage across the full range of macroscopic OA grade, from young healthy to aged severe OA donors, by bulk RNA sequencing of 92 knees, single-nucleus RNA sequencing of 108,600 chondrocyte nuclei from 30 donors and single-nucleus multiome sequencing of 24 of these donors, treating grade as a continuous variable. With increasing grade, cartilage increased extracellular matrix (ECM) synthesis and remodeling genes, lost glucocorticoid-responsive, lipid-metabolic and antioxidant programs, and changed the splicing of a small set of ECM transcripts, led by the extra domain B (EDB) exon of fibronectin (FN1). Nine chondrocyte clusters were present in every disease stage and formed a continuum ordered by cartilage zone and hypertrophic differentiation, with PRG4+ superficial and COL10A1+ hypertrophic chondrocytes as the only distinct cell types at its ends and a pre-hypertrophic state between them. With grade, all clusters shared a response in which ECM production rose and homeostatic programs fell, and they differed in which of its components was strongest: ECM production in the superficial cells, the secretory pathway in the hypertrophic and CYTL1+ cells, and inflammatory signaling in the ANXA1+ and CRISPLD2+ cells. Inferred communication between chondrocytes was remodeled with stage. FN1 was induced in every cluster in excess of its fibril-assembly machinery, together with the fibronectin-cleaving protease HTRA1, and FN1 signaling shifted in receptor use from integrin 5{beta}1 toward CD44 and, less robustly, v{beta}8, accompanied by a rise in TGF-{beta}/SMAD response genes. In four early-OA donors, tenascin-C was already largely induced and the FN1 receptor shift from 5{beta}1 toward CD44 was partly present, whereas the rise of FN1 outside superficial chondrocytes, of FGF1 and of developmental and ossification programs came with progression. Chromatin accessibility changed in the same direction across clusters, with regions linked to FN1 opening and regions linked to ITGA5 closing. OA progression in human cartilage therefore appears to be a change of chondrocyte state that differs in emphasis along a zonal and hypertrophic continuum and includes changes in fibronectin regulation, production, processing, and receptor engagement.

bioinformatics↗

bioRxiv2026

Single-nucleus multiome profiling reveals osteocyte-centered remodeling of human subchondral bone across osteoarthritis severity

Objective: Subchondral bone remodeling is a hallmark of osteoarthritis (OA), but osteocytes, the principal regulators of bone homeostasis, have been inaccessible to single-cell studies because they are embedded in mineralized matrix. We aimed to define the cellular, transcriptional and chromatin changes of human subchondral bone across OA severity, osteocytes included, and to identify candidate signals between cartilage and bone. Design: Subchondral bone from the medial femoral condyle of human knees graded by the Outerbridge system was analyzed by bulk RNA sequencing (89 knees) and by single-nucleus multiome sequencing of gene expression and chromatin accessibility after mechanical nuclear isolation (16 donors). Three hypotheses were prespecified: with increasing OA severity, (1) the osteoprogenitor fraction increases, (2) the osteocyte fraction increases, and (3) osteocyte SMAD2/3 motif activity increases. Results: With OA severity, bulk expression shifted toward extracellular matrix and ossification programs. The atlas resolved 26 cell states among 61,570 nuclei, including 906 osteocytes. Osteoprogenitors (p = 0.003) and osteocytes (p = 0.036) increased in share along an osteogenic continuum that starts from CXCL12-abundant reticular cells. Chondrocytes at the osteochondral junction upregulated FN1, FGF1, FGF2 and TNFSF11 without increased hypertrophic gene expression, and their share of the inferred FN1 signal received by osteocytes rose from 4% in normal knees to 33% in severe OA. Osteocyte SMAD2/3 motif activity increased with severity (rho = 0.70, p = 0.003), and all three hypotheses remained significant after Holm correction. Across the osteogenic lineage, SMAD2/3 activity correlated with junction chondrocyte FN1 (rho = 0.63, p = 0.017), and in osteocytes it was accompanied by TGF-{beta}-responsive matrix genes and perilacunar-remodeling genes. Conclusions: This osteocyte-inclusive atlas of human OA subchondral bone shows expansion of the osteogenic compartment and a rise of osteocyte SMAD2/3-linked matrix remodeling with disease, and identifies chondrocyte-derived FN1 as a candidate contributor to cartilage-bone communication associated with osteocyte TGF-{beta}/SMAD2/3 signaling.

molecular biology↗

bioRxiv2026

DRG meningeal tertiary lymphoid structures are regulated by B cells as a pronociceptive locus after peripheral nerve injury

B cell-derived IgG in the dorsal root ganglia (DRG) drives neuropathic pain after peripheral nerve injury (PNI), but the site of B cell organization is unclear. Here, PNI induced leukocyte clusters in the DRG meninges, enveloped by lymphatic endothelium and apposed to high endothelial venules. These clusters resemble tertiary lymphoid structures (TLSs) with germinal center-like features, including germinal center B cells and plasma cells, and follicular dendritic and follicular helper T cells. Single-cell RNA sequencing revealed enrichment of germinal center B cells in the DRG meninges after PNI. Germinal center B cells regulate TLS organization: TLSs were absent after deletion of Ezh2 from germinal center-experienced B cells. Intrathecal CD20 monoclonal antibody to locally deplete B cells also disrupted TLS organization. Conversely, intrathecal B cell transfer to B cell-deficient (muMT) mice was sufficient for TLS organization after PNI. Allodynia did not develop when TLS organization was disordered. Similar TLSs formed in pig DRG after tail docking and in human donors with chronic pain, where B cell receptor clonotype analysis confirmed functional maturity. Together, these data establish that germinal center B cells are required for TLS organization, and that disrupting this process abolishes the development of neuropathic pain after PNI.

neuroscience↗

bioRxiv2026

Synovial transcriptional clusters link cartilage degeneration to cell-type-specific gene expression in knee osteoarthritis

ObjectivesTo identify synovial transcriptional clusters in human knee osteoarthritis (OA) and determine how these relate to synovial histologic features, cell-type-associated gene expression, and cartilage degeneration severity. MethodsBulk RNA sequencing (RNA-seq) of synovial tissue from n = 135 patients with knee OA was analyzed using consensus clustering. Clusters were compared by clinical and histologic features, including cartilage degeneration severity (OARSI score). Single-cell RNA-seq (n = 18) and spatial transcriptomics were used to relate cartilage degeneration-associated gene expression patterns to synovial cell populations. ResultsFour synovial transcriptional clusters that differed in synovial histologic features and cartilage degeneration severity were identified. Greater cartilage degeneration was associated with enrichment of lining fibroblast- and inflammatory myeloid-associated gene expression, whereas lesser cartilage degeneration was associated with enrichment of sublining fibroblast, endothelial, mural cell, and adipocyte-associated gene expression. ConclusionsHuman knee OA synovium segregates into transcriptional clusters associated with cartilage degeneration severity. Synovial transcriptional heterogeneity corresponds to cell-type-associated gene expression. Key messagesO_ST_ABSWhat is already known on this topicC_ST_ABSO_LIOsteoarthritis synovium exhibits marked histologic and molecular heterogeneity. C_LIO_LISynovial inflammation detected by MRI correlates with cartilage degeneration and predicts progressive cartilage loss in knee OA. C_LIO_LIPrior transcriptomic studies have identified molecular subsets of OA synovium, but their relationship to cartilage degeneration severity remains unclear. C_LI What this study addsO_LIOA synovium segregates into four transcriptional clusters: Sublining (C1), Lymphomyeloid (C2), Myeloid (C3), and Major trauma (C4). C_LIO_LIGreater cartilage degeneration is associated with enrichment of inflammatory myeloid and lining fibroblast gene expression, whereas lesser degeneration is associated with enrichment of adipocyte, sublining fibroblast, endothelial, and mural cell-associated gene expression. C_LI How this study might affect research, practice or policyO_LIProvides a framework for a clinically relevant biological stratification of OA patients based on synovial molecular features. C_LIO_LIInforms future efforts to link synovial biology with OA prognosis, cartilage degeneration, treatment allocation, and development of targeted therapeutic strategies. C_LI

genomics↗

bioRxiv2025

Fast-conducting mechanonociceptors uniquely engage reflexive and affective pain circuitry to drive protective responses

Nociceptors detect damaging stimuli and evoke pain in healthy animals. We conducted an optogenetic activation screen to identify genetically defined nociceptor populations that elicit place aversion and nocifensive behaviors in response to stimulation. Smr2Cre- and Bmpr1bCre-labeled A{delta} high-threshold mechanoreceptors (HTMRs) emerged as two of the few nociceptor populations, and we focused on investigating their physiological, morphological, functional, and synaptic properties. These neurons densely innervate skin and other organs, are activated only by intense, potentially damaging stimuli, and are necessary for protective responses to sharp mechanical stimuli. Centrally, A{delta}-HTMRs projections span multiple spinal segments and terminate across spinal cord laminae, forming strong, monosynaptic connections onto anterolateral tract projection neurons, including antenna cells of the deep dorsal horn. A{delta}-HTMRs also engage a local spinal reflex circuit enabling a remarkably rapid limb withdrawal. Thus, A{delta}-HTMRs are myelinated nociceptors with unique properties that can be exploited for development of new analgesics.

neuroscience↗

bioRxiv2025

NERVE GROWTH FACTOR IS SUFFICIENT TO CAUSE MULTIPLE OSTEOARTHRITIS-RELEVANT PATHOLOGICAL FEATURES IN NAIVE MURINE KNEE JOINTS

BACKGROUNDNerve growth factor (NGF), a key mediator of pain and inflammation, is increased in joints with osteoarthritis (OA). Neutralizing NGF with monoclonal antibodies has shown analgesic effects in painful knee OA, but clinical development was stopped due to side effects in the joints. Knowledge about the biological effects of long-term exposure of joint tissues to NGF is limited. Therefore, we aimed to explore the effects of repeated intra-articular (IA) injections of NGF into the knee joints of healthy mice on pain and sensitization, as well as joint innervation and structure. METHODSWe conducted five experiments in male C57BL/6 mice. In Experiment 1, NGF (50ng or 500ng) or vehicle was injected IA into the knee of naive wildtype (WT) mice, twice a week for 4 weeks. We assessed knee swelling, knee hyperalgesia and histopathology. In Experiment 2, mice were injected with 500ng NGF or vehicle, twice a week for 4 weeks and microCT of the knee was performed. In Experiment 3, NaV1.8-tdTomato reporter mice were injected with 500ng NGF or vehicle, twice a week for 4 weeks, and joint innervation was assessed. In Experiment 4, WT mice received 500ng NGF or vehicle twice a week for 4 weeks and were used for single cell RNA sequencing (scRNAseq) of the synovium. In Experiment 5, L3-L5 DRGs of mice that received 3 IA injections of 500ng NGF or vehicle twice a week were used for bulk RNA sequencing. RESULTSRepeated bi-weekly IA injections of NGF caused knee hyperalgesia in naive mice. NGF caused dose-dependent knee swelling, synovial pathology, increased bone mineral density and trabecular bone thickness in the medial subchondral bone, growth of pre-osteophytes in the medial compartment, but no cartilage degeneration. NGF injection caused sprouting of NaV1.8+ neurons in the medial but not the lateral synovium. ScRNAseq of the synovium revealed upregulated genes related to neuronal sprouting, synovial fibrosis and ossification, confirming histopathological findings. Bulk RNA seq of DRG showed upregulated pathways related to axonal growth. CONCLUSIONSIn healthy mouse knees, NGF induced mechanical sensitization, synovitis, neoinnervation in the medial synovium, subchondral bone changes and pre-osteophyte growth in the medial compartment, thus capturing many pathological changes observed in OA, except cartilage damage.

neuroscience↗

bioRxiv2025

CD14 plays a critical role in pain and inflammation across multiple models of post-traumatic osteoarthritis

Inflammation is a primary driver of osteoarthritis (OA), and no therapies exist to halt or delay disease progression or substantially ameliorate the chronic pain, inflammation and disability that are characteristic of disease. Soluble CD14 (sCD14), a co-factor that enhances inflammatory toll-like receptor signaling, is present in synovial fluid in patients with OA and positively associates with joint space narrowing, synovial macrophage content, and pain. In this study, we show that increased sCD14 within human synovial fluid correlates with joint effusion volume and increased knee hyperalgesia. Next, we evaluated CD14 as a potential therapeutic target in three pre-clinical models of post traumatic OA (PTOA), using both genetic deficiency and pharmacologic blockade to modulate its activity. We demonstrate that deficiency or blockade of CD14 results in significant protection from increased evoked pain behaviors and from OA driven mobility impairments (i.e. decreased cage activity) across models that differ in severity, and across male and female cohorts. Using flow cytometry, single cell transcriptomics, and spatial proteomics, we further show that CD14-deficiency drastically influences the local synovial inflammatory landscape post-injury, reducing monocyte and macrophage populations and modulating local fibroblast populations. Targeting CD14 via genetic deficiency or therapeutic blockade revealed no substantial protection, but no worsening, of cartilage degeneration. Ultimately, our results provide strong support that targeting synovial inflammation through blockade of CD14 can safely ameliorate OA pain and disability after a pre-disposing injury. One Sentence SummaryThe study demonstrates the key role of CD14 in pain, mobility loss, and inflammation in PTOA, and demonstrates the therapeutic potential of CD14 blockade for OA pain relief.

immunology↗

bioRxiv2025

CXCL16 mediates nociception and inflammation in murine post-traumatic osteoarthritis

This study investigates the role of the chemokine CXCL16 and its receptor, CXCR6, in post-traumatic osteoarthritis (PTOA) and joint nociception, highlighting the potential of targeting the CXCL16-CXCR6 axis for therapeutically managing joint inflammation and pain. Following joint injury in mice, the CXCL16-CXCR6 signaling axis is activated in synovium, driven by synovial fibroblasts and macrophages. Human OA synovium also exhibited increased CXCL16 and CXCR6 gene expression. CXCL16 stimulated a pro-inflammatory response in fibroblasts and macrophages, contrasting with an anti-inflammatory response observed in mesenchymal progenitor cells. In mice, repeated intra-articular CXCL16 injections induced histological synovitis and sex-dependent activation of inflammatory and fibrotic transcriptional programs in synovium. Repeated CXCL16 joint injections also induced knee hyperalgesia, which was mitigated by co-administration of the CXCR6 antagonist, ML339. A single intra-articular injection of CXCL16 induced acute knee hyperalgesia as early as 30 minutes post-injection, which was completely abrogated by ML339 co-treatment, suggesting direct CXCL16 binding to nociceptor-expressed CXCR6. In a murine PTOA model, systemic CXCR6 antagonism with ML339 alleviated knee hyperalgesia and altered circulating immune cell profiles. Direct stimulation of mouse dorsal root ganglion-derived nociceptive neurons with CXCL16 induced rapid calcium signaling, which was abolished by co-treatment with ML339. These findings establish CXCL16 as a regulator of joint inflammation and identifies the CXCL16-CXCR6 binding mechanism as key in mediating pain-related behaviors and nociceptor activation, offering a therapeutic target for PTOA-related inflammation and pain management. One Sentence SummaryCXCL16 regulates synovial inflammation and mediates joint nociception via CXCR6, highlighting its potential as a therapeutic target for post-traumatic osteoarthritis.

physiology↗

bioRxiv2025

FM-dye inhibition of Piezo2 relieves acute inflammatory and osteoarthritis knee pain in mice of both sexes

Musculoskeletal pain is a significant burden affecting billions of people with little progress in the development of pharmaceutical pain relief options. The mechanically-activated ion channel Piezo2 has been shown to play a role in mechanical sensitization; however there has been little progress in examining therapeutics that target this molecule. The goal of this study was to assess the effect of two FM-dyes, FM1-43 or FM4-64, in reducing acute inflammatory and osteoarthritis knee joint pain in mice of both sexes. In our acute model of Complete Freunds adjuvant (CFA)-induced joint pain, mice intra-articularly injected with FM1-43 exhibited an attenuation of knee hyperalgesia 90 minutes following injection. In vivo calcium imaging of the dorsal root ganglion (DRG) also demonstrated a reduction in nociceptor responses to mechanical forces applied to the knee joint of CFA mice following FM-dye injection. Male and female WT mice subjected to partial medial meniscectomy (PMX) surgery as a model of osteoarthritis developed more severe knee hyperalgesia than nociceptor-specific Piezo2 conditional knock-out mice. Intra-articular injection of FM1-43 reduced both knee hyperalgesia and weight-bearing asymmetry in this model and had no effect in Piezo2 conditional knock-out mice. Finally, in mice with spontaneous osteoarthritis associated with aging, intra-articular injection of FM-dyes also reduced knee hyperalgesia. In conclusion, inhibiting Piezo2 genetically or pharmacologically was effective in reducing pain-related behaviors in mice of both sexes in the setting of inflammatory and osteoarthritis knee pain. These studies provide evidence of the therapeutic potential of targeting Piezo2 in musculoskeletal pain conditions.

neuroscience↗

bioRxiv2024

Acute systemic macrophage depletion in osteoarthritic mice alleviates pain-related behaviors and does not affect joint damage

BackgroundOsteoarthritis (OA) is a painful degenerative joint disease and a leading source of years lived with disability globally due to inadequate treatment options. Neuroimmune interactions reportedly contribute to OA pain pathogenesis. Notably, in rodents, macrophages in the DRG are associated with onset of persistent OA pain. Our objective was to determine the effects of acute systemic macrophage depletion on pain-related behaviors and joint damage using surgical mouse models in both sexes. MethodsWe depleted CSF1R+ macrophages by treating male macrophage Fas-induced apoptosis (MaFIA) transgenic mice 8-or 16-weeks post destabilization of the medial meniscus (DMM) with AP20187 or vehicle control (10 mg/kg i.p., 1x/day for 5 days), or treating female MaFIA mice 12 weeks post partial meniscectomy (PMX) with AP20187 or vehicle control. We measured pain-related behaviors 1-3 days before and after depletion, and, 3-4 days after the last injection we examined joint histopathology and performed flow cytometry of the dorsal root ganglia (DRGs). In a separate cohort of male 8-week DMM mice or age-matched naive vehicle controls, we conducted DRG bulk RNA-sequencing analyses after the 5-day vehicle or AP20187 treatment. ResultsEight-and 16-weeks post DMM in male mice, AP20187-induced macrophage depletion resulted in attenuated mechanical allodynia and knee hyperalgesia. Female mice showed alleviation of mechanical allodynia, knee hyperalgesia, and weight bearing deficits after macrophage depletion at 12 weeks post PMX. Macrophage depletion did not affect the degree of cartilage degeneration, osteophyte width, or synovitis in either sex. Flow cytometry of the DRG revealed that macrophages and neutrophils were reduced after AP20187 treatment. In addition, in the DRG, only MHCII+ M1-like macrophages were significantly decreased, while CD163+MHCII-M2-like macrophages were not affected in both sexes. DRG bulk RNA-seq revealed that Cxcl10 and Il1b were upregulated with DMM surgery compared to naive mice, and downregulated in DMM after acute macrophage depletion. ConclusionsAcute systemic macrophage depletion reduced the levels of pro-inflammatory macrophages in the DRG and alleviated pain-related behaviors in established surgically induced OA in mice of both sexes, without affecting joint damage. Overall, these studies provide insight into immune cell regulation in the DRG during OA.

neuroscience↗

bioRxiv2024

Fluorescein-Based SynNotch Adaptors for Regulating Gene Expression Responses to Diverse Extracellular Cues

We introduce an adaptor-based strategy for regulating fluorescein-binding synthetic Notch (SynNotch) receptors using ligands based on conjugates of fluorescein isomers and analogs. To develop a versatile system, we evaluated the surface expression and activities of multiple constructs containing distinct extracellular fluorescein-binding domains. Using an optimized receptor, we devised ways to regulate signaling via fluorescein-based chemical transformations, including an approach based on a bio-orthogonal chemical ligation and a spatially controllable strategy via the photo-patterned uncaging of an o-nitrobenzyl-caged fluorescein conjugate. We further demonstrate that fluorescein-conjugated extracellular matrix (ECM)-binding peptides can regulate SynNotch activity depending on the folding state of collagen-based ECM networks. Treatment with these conjugates enabled cells to distinguish between folded versus denatured collagen proteins and enact dose-dependent gene expression responses depending on the nature of the signaling adaptors presented. To demonstrate the utility of these tools, we applied them to control the myogenic conversion of fibroblasts into myocytes with spatial and temporal precision and in response to denatured collagen-I, a biomarker of multiple pathological states. Overall, we introduce an optimized fluorescein-binding SynNotch as a versatile tool for regulating transcriptional responses to extracellular ligands based on the widely used and clinically-approved fluorescein dye.

synthetic biology↗

bioRxiv2024

Reduced Capsaicin-Induced Mechanical Allodynia and Neuronal Responses in the DRG in the Presence of Shp1 Overexpression

Transient Receptor Potential Vanilloid 1 (TRPV1) is a nonselective cation channel expressed by pain-sensing neurons and has been an attractive target for the development of drugs to treat pain. Recently, Src homology region 2 domain-containing phosphatase-1 (SHP-1) was shown to dephosphorylate TRPV1 in dorsal root ganglia (DRG) neurons, which was linked with alleviating different pain phenotypes. These previous studies were performed in male rodents only and did not directly investigate the role of SHP-1 in TRPV-1 mediated sensitization. Therefore, our goal was to determine the impact of Shp1 overexpression on TRPV1-mediated neuronal responses and capsaicin-induced pain behavior in mice of both sexes. Twelve-week-old male and female mice overexpressing Shp1 (Shp1-Tg) and their wild type (WT) littermates were used. Shp1 overexpression was confirmed in the DRG of Shp1-Tg mice by RNA in situ hybridization and RT-qPCR. Trpv1 and Shp1 were found to be co-expressed in DRG sensory neurons in both genotypes. Functionally, this overexpression resulted in lower magnitude intracellular calcium responses to 200 nM capsaicin stimulation in DRG cultures from Shp1-Tg mice compared to WTs. In vivo, we tested the effects of Shp1 overexpression on capsaicin-induced pain through a model of capsaicin footpad injection. While capsaicin injection evoked nocifensive behavior (paw licking) and paw swelling in both genotypes and sexes, only WT mice developed mechanical allodynia after capsaicin injection. We observed similar level of TRPV1 protein expression in the DRG of both genotypes, however, a higher amount of tyrosine phosphorylated TRPV1 was detected in WT DRG. These experiments suggest that, while SHP-1 does not mediate the acute swelling and nocifensive behavior induced by capsaicin, it does mediate a protective effect against capsaicin-induced mechanical allodynia in both sexes. The protective effect of SHP-1 might be mediated by TRPV1 dephosphorylation in capsaicin-sensitive sensory neurons of the DRG.

neuroscience↗

bioRxiv2023

Recommendations For a Standardized Approach to Histopathologic Evaluation of Synovial Membrane in Murine Models of Experimental Osteoarthritis

BackgroundSynovial pathology has been linked to osteoarthritis (OA) pain in patients. Microscopic grading systems for synovial changes in human OA have been described, but a standardized approach for murine models of OA is needed. We sought to develop a reproducible approach and set of minimum recommendations for synovial histopathology in mouse models of OA. MethodsCoronal and sagittal sections from male mouse knee joints subjected to destabilization of medial meniscus (DMM) or partial meniscectomy (PMX) were collected as part of other studies. Stains included Hematoxylin and Eosin (H&E), Toluidine Blue (T- Blue) and Safranin O/Fast Green (Saf-O). Four blinded readers graded pathological features (hyperplasia, cellularity, and fibrosis) at specific anatomic locations in the medial and lateral compartments. Inter-reader reliability of each feature was determined. ResultsThere was acceptable to very good agreement between raters. After DMM, increased hyperplasia and cellularity and a trend towards increased fibrosis were observed 6 weeks after DMM in the medial locations, and persisted up to 16 weeks. In the PMX model, cellularity and hyperplasia were evident in both medial and lateral compartments while fibrotic changes were largely seen on the medial side. Synovial changes were consistent from section to section in the mid-joint area mice. H&E, T-blue, and Saf-O stains resulted in comparable reliability. ConclusionsTo allow for a standard evaluation that can be implemented and compared across labs and studies, we recommend using 3 readers to evaluate a minimum set of 3 pathological features at standardized anatomic areas. Pre-defining areas to be scored, and reliability for each pathologic feature should be considered.

pathology↗

bioRxiv2022

A subpopulation of peripheral sensory neurons expressing the Mas-related G Protein-Coupled Receptor d (Mrgprd) generates pain hypersensitivity in painful diabetic neuropathy.

Painful diabetic neuropathy (PDN) is one of the most common and intractable complications of diabetes. PDN is characterized by neuropathic pain accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability, axonal degeneration, and loss of cutaneous innervation. However, the complete molecular profile underlying the hyper-excitable cellular phenotype of DRG nociceptors in PDN has not been elucidated. This gap in our knowledge is a critical barrier to developing effective, mechanism-based, and disease-modifying therapeutic approaches which are urgently needed to relieve the symptoms of PDN. Using single-cell RNA sequencing we demonstrated an increased expression of the Mas-related G Protein-Coupled Receptor d (Mrgprd) in a subpopulation of DRG neurons in the well-established High-Fat Diet (HFD) mouse model of PDN. In vivo calcium imaging allowed us to demonstrate that activation of Mrgprd receptors expressed by cutaneous afferents produced DRG neuron hyper-excitability and oscillatory calcium waves. Furthermore, Mrgprd-positive cutaneous afferents persist in diabetic mice skin. Importantly, limiting Mrgprd signaling or Mrgprd-positive DRG neuron excitability, reversed mechanical allodynia in the HFD mouse model of PDN. Taken together, our data highlights a key role of Mrgprd-mediated DRG neuron excitability in the generation and maintenance of neuropathic pain in a mouse model of PDN. Hence, we propose Mrgprd as a promising accessible target for developing effective therapeutics currently unavailable for treating neuropathic pain in PDN. Furthermore, understanding which DRG neurons cell type is mediating mechanical allodynia in PDN is of fundamental importance to our basic understanding of somatosensation and may provide an important way forward for identifying cell-type-specific therapeutics to optimize neuropathic pain treatment and nerve regeneration in PDN.

neuroscience↗

bioRxiv2022

The matrisome of the murine and human dorsal root ganglion: a transcriptomal approach

The extracellular matrix (ECM) is a dynamic structure composed of a large number of molecules that can be divided into six different categories and are collectively called the matrisome. The ECM plays pivotal roles in physiological and pathological processes in many tissues, including the nervous system. Intriguingly, alterations in ECM molecules/pathways are often associated with painful human conditions and murine experimental pain models. Nevertheless, mechanistic insight into the interplay of normal or defective ECM and pain is largely lacking. To expand the knowledge on ECM composition and synthesis in the peripheral nervous system, we used a transcriptomal approach to investigate the expression and cellular origin of matrisome genes in murine and human dorsal root ganglia (DRG), containing the cell bodies of sensory neurons. Bulk RNA sequencing data showed that over 60% of all matrisome genes were expressed in both murine and human DRG, with proportionally more core matrisome genes (glycoproteins, collagens, and proteoglycans) expressed compared to matrisome-associated genes (ECM-affiliated genes, ECM regulators and secreted factors). Examination of the cellular origin of matrisome expression by single cell RNA sequencing on murine DRG revealed that core matrisome genes, especially collagens, were expressed by vascular leptomeningeal-like (fibroblast) cell types whereas matrisome-associated genes were mainly expressed by neuronal cell types. We analyzed cell-cell communication networks with the CellChat R package and predicted an important role for the Collagen signaling pathway in connecting vascular cell types and nociceptors in murine tissue, which we confirmed by analysis of spatial transcriptomic data from human DRG. RNAscope in situ hybridization and immunohistochemistry confirmed expression of collagens in fibroblasts surrounding nociceptors in human DRG. This study supports the idea that the DRG matrisome may contribute to neuronal signaling in both mouse and human. The identification of the cellular distribution of murine and human matrisome genes provides a framework to study the role of the ECM in peripheral nervous tissue and its effects on pain signaling. HighlightsO_LITranscriptomal analyses of mouse and human dorsal root ganglia (DRG) revealed that over 60% of matrisome genes are expressed by murine and human dorsal root ganglia (DRG), with over 85% of the genes with orthologues overlapping between both species. C_LIO_LIMatrisome-associated genes had the highest expression in both species and included conserved expression of annexins, S100 calcium binding proteins and cathepsins. C_LIO_LICollagens and collagen receptors are expressed by distinct cell types in murine and human DRG, suggesting that the collagen signaling pathway could be involved in cell-cell signaling. C_LI

neuroscience↗

bioRxiv2022

Age-associated changes in knee osteoarthritis, pain-related behaviors, and dorsal root ganglia immunophenotyping of male and female mice

ObjectiveOsteoarthritis (OA) is a leading cause of chronic pain, yet OA pain management remains poor. Age is the strongest predictor of OA development, and mechanisms driving OA pain are unclear. While injury-induced OA models are useful, only a subset of OA is linked to traumatic injury. Here, we aimed to characterize age-associated joint damage, mechanical sensitization, and dorsal root ganglia (DRG) immune phenotypes in mice of both sexes. MethodsMale or female mice aged 6- or 20-months old were evaluated for histopathologic knee OA, pain-related behaviors, and L3-L5 dorsal root ganglia (DRG) immune characterization via flow cytometry. DRG gene expression in aged mice and humans was also examined. ResultsTwenty-month old male mice had worse cartilage degeneration than 6-month old mice. Older female knees showed increased cartilage degeneration, but to a lesser degree than males. Older mice of both sexes had worse mechanical allodynia, knee hyperalgesia, and grip strength compared to younger mice. For both sexes, DRGs from older mice showed decreased CD45+ cells, and a significant increase in F4/80+ macrophages and CD11c+ dendritic cells. Older male DRGs showed increased expression of Ccl2 and Ccl5 and older female DRGs showed increased Cxcr4 and Ccl3 compared to 6-month DRGs, among other differentially expresssed genes. Human DRG analysis from six individuals >80 years old revealed elevated CCL2 in male DRGs compared to females, whereas CCL3 was higher in female DRGs. ConclusionsHere we show that aging in male and female mice is accompanied by mild knee OA, mechanical sensitization, and changes to immune cell populations in the DRG, suggesting novel avenues for development of analgesic therapies.

cell biology↗

bioRxiv2022

Piezo2 expressing nociceptors mediate mechanical sensitization in experimental osteoarthritis

Osteoarthritis is a very common painful joint disease, for which few treatment options exist. New non-opioid targets are needed for addressing osteoarthritis pain, which is mechanical in nature and associated with daily activities such as walking and climbing stairs. Piezo2 has been implicated in development of mechanical pain, but the mechanisms by which this occurs remain poorly understood. We observed that in two different murine models of osteoarthritis (destabilization of the medial meniscus and natural aging), nociceptor-specific Piezo2 conditional knock-out mice developed osteoarthritic joint damage, but were protected from associated mechanical sensitization. Since nerve growth factor (NGF) is known to mediate nociceptor sensitization, and antibodies that neutralize NGF are effective as a treatment for osteoarthritis pain, we explored the effects of intra-articularly injected NGF on the development of mechanical joint pain. Wild-type mice developed knee swelling and mechanical pain in response to intra-articular NGF, while nociceptor-specific Piezo2 conditional knock-out mice were protected from these effects. Single cell RNA sequencing and in situ hybridization of mouse and human lumbar dorsal root ganglia (DRG) revealed that a subset of nociceptors co-express Piezo2 and Ntrk1 (the gene that encodes the NGF receptor TrkA). These results indicate that Piezo2 plays a key role in nociceptor sensitization processes in the osteoarthritic joint, and targeting Piezo2 may represent a novel therapy for osteoarthritis pain control. One Sentence SummaryNociceptor sensitization to mechanical stimuli is dependent on Piezo2 in mouse models of osteoarthritis.

physiology↗

bioRxiv2021

Diversification of ergot alkaloids and heritable fungal symbionts in morning glories

Heritable microorganisms play critical roles in life cycles of many macro-organisms but their prevalence and functional roles are unknown for most plants. Bioactive ergot alkaloids produced by heritable Periglandula fungi occur in some morning glories (Convolvulaceae), similar to ergot alkaloids in grasses infected with related fungi. Ergot alkaloids have been of longstanding interest given their toxic effects, psychoactive properties, and medical applications. Here we show that ergot alkaloids are concentrated in four morning glory clades exhibiting differences in alkaloid profiles and are more prevalent in species with larger seeds than those with smaller seeds. Further, we found a phylogenetically-independent, positive correlation between seed mass and alkaloid concentrations in symbiotic species. Our findings suggest that heritable symbiosis has diversified among particular clades by vertical transmission through seeds combined with host speciation, and that ergot alkaloids are particularly beneficial to species with larger seeds. Our results are consistent with the defensive symbiosis hypothesis where bioactive ergot alkaloids from Periglandula symbionts protect seeds and seedlings from natural enemies, and provide a framework for exploring microbial chemistry in other plant-microbe interactions.

plant biology↗