Biology subjects

Thomson, B. R.

Publications and source records attributed to Thomson, B. R..

7 recordsLinked to original sources

bioRxiv2026

VEGFA-Positive Macrophages Regulate Aqueous Humor Outflow in Aged Mice and Humans

Elevated intraocular pressure (IOP) and aging are major risk factors for primary open-angle glaucoma (POAG), but how aging affects IOP regulation remains poorly understood. IOP remains within a narrow range despite age-associated changes predicted to increase aqueous humor outflow (AHO) resistance at the interface between the trabecular meshwork and Schlemm's canal (SC), suggesting compensatory mechanisms preserve AHO homeostasis during aging. Single-cell RNA sequencing of mouse ocular angle tissues revealed immunomodulatory transcriptional reprogramming of SC endothelial cells in older mice, while mouse and human imaging showed reduced SC size and increased peri-SC macrophage accumulation with aging. Ligand-receptor analysis predicted enhanced macrophage-to-SC VEGFA-VEGFR signaling in aged and Tie2-haploinsufficient mice, an independent model of vascular stress and glaucoma risk. Deletion of Vegfa in CX3CR1+ macrophages increased IOP and reduced AHO facility in 9-month-old mice, demonstrating that macrophage-derived VEGFA supports AHO homeostasis. Tie2 haploinsufficiency recapitulated key age-associated SC niche changes, including peri-SC macrophage accumulation, whereas gene therapy boosting TIE2 activity protected wild-type mice against age-related changes. Together, these findings identify peri-SC macrophage-derived VEGFA as a compensatory mechanism maintaining AHO homeostasis during aging and vascular stress and support TIE2 activation as a therapeutic strategy to preserve SC function and IOP regulation.

physiology↗

bioRxiv2025

PROX1 loss in adult mouse Schlemm's canal causes permanent ocular hypertension

Glaucoma is associated with ocular hypertension and lowering intraocular pressure is a key objective of glaucoma therapies. Recent studies have established a role for the Schlemms canal endothelium in this pressure increase and have shown it to have a unique, lymphatic-like, hybrid phenotype. However, the role of these lymphatic phenotypes in the adult canal remains uncertain. Long-term functional studies have been limited by systemic importance of lymphatic genes and lack of Schlemms canal-specific animal models. Here, we designed and validated a strategy using 4OH-tamoxifen-loaded nanocarriers to generate targeted, Schlemms canal specific knockout mice lacking lymphatic phenotypes. Using this system, we selectively deleted Prox1, the master transcription factor governing lymphatic fate. Within four weeks, intraocular pressure significantly increased, and ocular hypertension was maintained for at least 24 weeks. Unlike lymphatic vessels, which degenerate following Prox1 deletion, Schlemms canal reverted to a less functional vein-like phenotype with no change in size or morphology. These results highlight the utility of nanocarriers for tissue-specific genetic recombination and demonstrate that changes in lymphatic phenotypes alter intraocular pressure, providing new targets for glaucoma therapy. Moreover, as we found that PROX1 was downregulated with age in human Schlemms canal, these canal-specific conditional Prox1 knockout mice are a valuable new adult-onset model of ocular hypertension that captures key features of age-related human disease.

physiology↗

bioRxiv2025

Piezo1 Activates an Autocrine Angiopoietin-2-Integrin Signaling Loop in Schlemm's Canal to Regulate Intraocular Pressure

Elevated intraocular pressure (IOP), driven by increased outflow resistance in the trabecular meshwork and Schlemms canal (SC), is a primary risk factor for glaucoma. This resistance is regulated by broadly active endothelial signaling systems such as ANGPT1-TIE2 and by dynamic flow-responsive pathways that remain poorly understood. Here, we identify a previously unrecognized, TIE2-independent, mechanosensitive ANGPT2-integrin 9{beta}1 pathway in the SC endothelium that regulates IOP. In vitro and in vivo, we show that activation of the mechanosensory channel PIEZO1 triggers ANGPT2 secretion and promotes cell-surface clustering of integrin 9{beta}1. Deletion of SC-expressed Piezo1 or Itga9 in mice resulted in SC narrowing, impaired flow-mediated SC endothelial proliferation, IOP elevation and glaucoma. Furthermore, ANGPT2 deficiency or blockade disrupted PIEZO1-induced integrin activation and reduced aqueous humor outflow facility. These findings establish autocrine PIEZO1-ANGPT2-ITGA9 signaling as a link between mechanosensory stimuli, SC structure and IOP regulation, offering promising new targets for glaucoma therapy.

cell biology↗

bioRxiv2025

Filomicelle-Embedded Composite Hydrogels for Localized Gelation within the Anterior Chamber of the Eye

Nanocarriers hold transformative potential for treating anterior segment eye diseases, yet corneal epithelium impermeability necessitates intraocular injection. Given the discomfort and infection risk, an injectable hydrogel-based depot offers a promising strategy for sustained nanocarrier delivery in intraocular therapy. However, because the aqueous humor is a large, fluid-filled environment, achieving spatially confined gelation remains a key challenge as injected materials rapidly diffuse. Herein, we present a composite hydrogel (C-gel) that enables localized in situ gelation and sustained nanocarrier release within the anterior chamber. This is achieved using poly(ethylene glycol)-b-poly(propylene sulfide) (PEG-b-PPS) filomicelles (FMs), whose filamentous structure confines crosslinking reactions spatially, promoting efficient gel formation. As a result, 90% of the injected polymer is retained within the crosslinked hydrogel matrix. Embedded FMs then undergo oxidation-induced cylinder-to-sphere transitions, facilitating gradual release of micellar nanocarriers. The rheological properties, gelation timing, and microstructure of the C-gel are adjustable, allowing precise control of nanocarrier release dynamics. In vivo evaluation in mice confirmed excellent biocompatibility without inducing intraocular pressure elevation, ocular toxicity, or immune cell infiltration. Sustained release of nanocarriers was observed for over a month under conditions mimicking that of the anterior chamber of the eye, underscoring the potential of C-gels for long-term drug delivery in anterior segment eye diseases therapy.

bioengineering↗

bioRxiv2024

Non-endothelial expression of Endomucin in the mouse and human choroid

Endomucin (EMCN) is a 261 AA transmembrane glycoprotein that is highly expressed by venous and capillary endothelial cells where it plays a role in VEGF-mediated angiogenesis and regulation of immune cell recruitment. However, it is better known as a histological marker, where it has become widespread due to the commercial availability of high-quality antibodies that work under a wide range of conditions and in many tissues. The specificity of EMCN staining has been well-validated in retinal vessels, but while it has been used extensively as a marker in other tissues of the eye, including the choroid, the pattern of expression has not been described in detail. Here, in addition to endothelial expression in the choriocapillaris and deeper vascular layers, we characterize a population of EMCN-positive perivascular cells in the mouse choroid that did not co-localize with cells expressing other endothelial markers such as PECAM1 or PODXL. To confirm that these cells represented a new population of EMCN-expressing stromal cells, we then performed single cell RNA sequencing in choroids from adult wild-type mice. Analysis of this new dataset confirmed that, in addition to endothelial cells, Emcn mRNA expression was present in choroidal pericytes and a subset of fibroblasts, but not vascular smooth muscle cells. Besides Emcn, no known endothelial gene expression was detected in these cell populations, confirming that they did not represent endothelial-stromal doublets, a common technical artifact in single cell RNA seq datasets. Instead, choroidal Emcn-expressing fibroblasts exhibited high levels of chemokine and interferon signaling genes, while Emcn-negative fibroblasts were enriched in genes encoding extracellular matrix proteins. Emcn expressing fibroblasts were also detected in published datasets from mouse brain and human choroid, suggesting that stromal Emcn expression was not unique to the choroid and was evolutionarily conserved. Together, these findings highlight unique fibroblast and pericyte populations in the choroid and provide new context for the role of EMCN in angiogenesis and immune cell recruitment.

cell biology↗

bioRxiv2022

MyD88-TLR4-dependent choroid plexus activation precedes perilesional inflammation and edema in intracerebral hemorrhage

The functional neurological outcome of patients with intracerebral hemorrhage (ICH) strongly relates to the degree of secondary brain injury (ICH-SBI) evolving within days after the initial bleeding. Different mechanisms including the incitement of inflammatory pathways, dysfunction of the blood-brain barrier (BBB), activation of resident microglia, and an influx of blood-borne immune cells, have been hypothesized to contribute to ICH-SBI. Yet, the spatiotemporal interplay of specific inflammatory processes within different brain compartments has not been sufficiently characterized, limiting potential therapeutic interventions to prevent and treat ICH-SBI. Using a whole-blood injection model in mice, we systematically characterized the spatial and temporal dynamics of inflammatory processes after ICH using 7-Tesla magnetic resonance imaging (MRI), spatial RNA sequencing (spRNAseq), functional BBB assessment, and immunofluorescence average-intensity-mapping. We identified a pronounced early response of the choroid plexus (CP) peaking at 12 to 24h, that was characterized by inflammatory cytokine expression, epithelial and endothelial expression of leukocyte adhesion molecules, and the accumulation of leukocytes. In contrast, we observed a delayed secondary reaction pattern at the injection site (striatum) peaking at 96h, defined by gene expression corresponding to perilesional leukocyte infiltration and correlating to the delayed signal alteration seen on MRI. Pathway analysis revealed a dependence of the early inflammatory reaction in the CP on toll-like receptor 4 (TLR4) signaling via myeloid differentiation factor 88 (MyD88). TLR4 and MyD88 knockout mice corroborated this observation, lacking the early upregulation of adhesion molecules and leukocyte infiltration within the CP 24h after whole-blood injection. In conclusion, we report a biphasic brain reaction pattern after ICH with a MyD88-TLR4-dependent early inflammatory response of the CP, preceding inflammation, edema and leukocyte infiltration at the lesion site. Pharmacological targeting of the early CP-activation might harbor the potential to modulate the development of ICH-SBI. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=83 SRC="FIGDIR/small/506660v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@195554corg.highwire.dtl.DTLVardef@1130d16org.highwire.dtl.DTLVardef@1c03678org.highwire.dtl.DTLVardef@381ff4_HPS_FORMAT_FIGEXP M_FIG C_FIG Akeret, Buzzi et al. characterized the spatiotemporal dynamics after striatal whole blood injection in mice using magnetic resonance imaging (MRI), spatial RNA sequencing (spRNAseq), functional blood-brain barrier (BBB) assessment, and immunofluorescence average intensity mapping (IF). They report a biphasic brain reaction pattern with an early MyD88-TLR4-dependent inflammatory response of the CP, which preceded secondary inflammation and leukocyte infiltration at the perilesional site.

neuroscience↗

bioRxiv2022

Blood oxygenation-level dependent cerebrovascular reactivity imaging as strategy to monitor CSF-hemoglobin toxicity

PurposeCell-free hemoglobin in the cerebrospinal fluid (CSF-Hb) may be one of the main drivers of secondary brain injury after aneurysmal subarachnoid hemorrhage. Haptoglobin scavenging of CSF-Hb has been shown to mitigate cerebrovascular disruption. Using digital subtraction angiography (DSA) and blood oxygenation-level dependent cerebrovascular reactivity imaging (BOLD-CVR) the aim was to assess the acute toxic effect of CSF-Hb on cerebral blood flow and autoregulation, as well as to test the protective effects of haptoglobin. MethodsDSA imaging was performed in eight anesthetized and ventilated sheep (mean weight: 80.4 kg) at baseline, 15, 30, 45 and 60 minutes after infusion of hemoglobin (Hb) or co-infusion with haptoglobin (Hb:Haptoglobin) into the left lateral ventricle. Additionally, 10 ventilated sheep (mean weight: 79.8 kg) underwent BOLD-CVR imaging to assess the cerebrovascular reserve capacity. ResultsDSA imaging did not show a difference in mean transit time or cerebral blood flow. Wholebrain BOLD-CVR compared to baseline decreased more in the Hb group after 15 minutes (Hb vs Hb:Haptoglobin: -0.03 {+/-}0.01 vs -0.01 {+/-}0.02) and remained diminished compared to Hb:Haptoglobin group after 30 minutes (Hb vs Hb:Haptoglobin: -0.03 {+/-}0.01 vs 0.0 {+/-}0.01), 45 minutes (Hb vs Hb:Haptoglobin: -0.03 {+/-}0.01 vs 0.01 {+/-}0.02) and 60 minutes (Hb vs Hb:Haptoglobin: -0.03 {+/-}0.02 vs 0.01 {+/-}0.01). ConclusionIt is demonstrated that CSF-Hb toxicity leads to rapid cerebrovascular reactivity impairment, which is blunted by haptoglobin co-infusion. BOLD-CVR may therefore be further evaluated as a monitoring strategy for CSF-Hb toxicity after aSAH.

neuroscience↗