Biology subjects

Brooks, D. J.

Publications and source records attributed to Brooks, D. J..

14 recordsLinked to original sources

bioRxiv2026

Intermittent parathyroid hormone employs autonomous and non-autonomous mechanisms to drive osteogenesis from Ebf3-expressing skeletal progenitor cells

How systemic hormonal signals coordinate stem cell fate decisions in adult tissues remains incompletely understood. In bone marrow, Cxcl12-abundant reticular (CAR) cells, marked by Early B-cell Factor 3 (Ebf3) expression, are multipotent mesenchymal progenitors that maintain the hematopoietic stem cell niche and serves as a major osteoblast progenitor source during adult bone remodeling. Using inducible lineage tracing coupled with single-cell transcriptomics and conditional genetics in mice, we show that intermittent parathyroid hormone (iPTH; teriparatide) drives osteogenesis from CAR cells by simultaneously engaging cell-intrinsic and cell-extrinsic mechanisms. Directly, iPTH suppresses lineage-enforcing transcription factors Ebf3, Ebf1, and Foxc1, thereby destabilizing progenitor identity and priming CAR cells for osteogenic commitment. Simultaneously, iPTH stimulates osteoclastic bone resorption, releasing TGF{beta} which recruits these primed progenitors to bone surfaces, a process abolished by osteoclast depletion. Preventing CAR cell maturation via Sp7 deletion abrogates iPTH-induced bone gain, establishing these progenitors as essential mediators of bone anabolism. This coupled mechanism, in which intrinsic transcriptional priming converges with extrinsic niche remodeling, is conserved in human CAR cells from teriparatide-treated postmenopausal women, which show concordant suppression of EBF3 and FOXC1 and elevated TGF{beta}-responsive gene signatures. These findings reveal a general principle by which a systemic hormone orchestrates tissue remodeling through simultaneous reprogramming of progenitor identity and remodeling of the niche microenvironment.

physiology↗

bioRxiv2026

Short- and Long-Term Effects of Social Isolation on Adult Murine Bone are Sex-Dependent

Social isolation is a known modifiable risk factor for many chronic diseases including cardiovascular, metabolic, and neurological disorders. Recent research has demonstrated that social isolation is similarly detrimental to skeletal health, but these effects may be sexually dimorphic. In rodents, isolation negatively affects bone in adult male mice, but not in females. However, these sex differences have not been systematically investigated, and it is unknown if they persist with long-term social isolation. The goal of our study was to investigate if isolation-induced bone loss may occur on different timescales between female and male mice, as well as investigate the potential roles of estrogen and testosterone. We examined bone changes in grouped (4 mice/cage) or isolated (1 mouse/cage) female and male 16-week-old C57BL/6J mice after 2, 4, or 8 weeks of treatment. We found that social isolation through single housing significantly reduced bone parameters across treatment lengths in male mice (20% average reduction in Tb.BV/TV; 8% average reduction in Ct.Th.) but not in females even with prolonged isolation. In trabecular bone, isolation affected male bone parameters in as little as 2 weeks. Isolation also decreased biomechanical properties in the femur of male but not female mice. While the females overall bone phenotype was unaffected, isolated females did show an increase in bone turnover markers with 2 weeks of isolation. Isolation also altered estrogen-related gene expression in male mice isolated for 4 or 8 weeks. Overall, our results demonstrate that both short- and long-term social isolation has sexually dimorphic effects on murine bone. These findings have important clinical implications for individuals at risk for social isolation, as well as for pre-clinical rodent models utilizing single housing. Lay SummarySocial isolation may have worse effects on bone in males than females, but this has not been thoroughly explored. We investigated if different lengths of isolation had different effects on the bones of male and female mice. We found that both short- and long-term isolation had a rapid and negative impact on the bones of male but not female mice, although isolated females did show some changes in markers of bone formation and resorption. These findings have important implications for humans at risk for social isolation, as well as for studies with rodents that use single housing.

physiology↗

bioRxiv2026

Deletion of Dock7 Exons 3 and 4 Results in Reduced Trabecular Microarchitecture and a Decrease in Mineralization

Dedicator of Cytokinesis 7 (DOCK7) has recently emerged as a regulator of skeletal homeostasis, but existing Dock7 mutant models harbor only global mutations and are incompatible with tissue-specific deletion studies. We previously generated a Dock7-floxed allele in which exons 3-4 are flanked by LoxP sites. To validate the utility of this allele for future conditional strategies, we globally deleted exons 3-4 to generate Dock7em2/em2 mice and characterized their skeletal phenotype. Homozygous Dock7em2/em2 mice exhibited a diluted coat color and white belly spot, consistent with spontaneous Dock7 mutations, whereas heterozygotes exhibited no spotting or coat changes. Bone microarchitecture was assessed in 21-week-old males and females. Global deletion of Dock7 exons 3-4 resulted in a 30-37% reduction in trabecular bone volume in the distal femur and L5 vertebrae. Cortical bone thickness was unchanged, though sex-specific alterations in femoral area suggested altered appositional bone growth. Mass spectrometry (SWATH) analysis of Dock7em2/em2 bone marrow stromal cells (BMSCs) identified DOCK7 protein levels similar to control mice, likely resulting from an alternative translational start site. Despite stable protein abundance prior to differentiation, BMSCs from Dock7em2/em2 mice exhibited reduced mineralization and decreased Bglap expression, indicating attenuated osteoblast differentiation. These findings demonstrate that Dock7 exons 3-4 are required for normal trabecular bone acquisition and osteoblast function. While the Dock7-em2 allele likely encodes a truncated protein product, its recapitulation of the Misty skeletal phenotype confirms that exons 3-4 are essential for DOCK7 activity. These studies in the Dock7em2/em2 mouse provide a foundation for future tissue-specific deletion studies utilizing the Dock7 exon 3-4 deletion model to define the cellular roles of DOCK7 in regulating bone formation and trabecular architecture. Lay SummaryIdentifying genes that regulate bone mass is essential for understanding osteoporosis. Mutation of the Dock7 gene in mice results in low bone mass, similar to human osteoporosis. Previous models could not isolate its role in specific tissues, limiting our ability to understand how DOCK7 controls bone mass. We developed a new mouse model where Dock7 can be mutated in specific tissues. In this study, we bred mice to carry this mutation across all tissues, causing significant bone loss. This validates a flexible tool for future research to mutate DOCK7 in specific cell types and map its role in skeletal health.

cell biology↗

bioRxiv2025

Age-specific Aβ-Tau interactions underlie spatial memory deficits in an APP/PS1 amyloidosis model

BackgroundAmyloid-{beta} (A{beta}) and tau pathology are key molecular hallmarks of Alzheimers disease (AD), yet how their interaction contributes to cognitive decline remains unclear. We investigated the relationship between A{beta} burden, tau pathology, presynaptic density, and spatial learning and memory in the APPswe/PSEN1{Delta}E9 (APP/PS1) transgenic (TG) mouse model of amyloidosis. MethodsSpatial learning and memory were assessed with the Barnes maze test in male TG and wild-type (WT) littermate mice, aged 6, 12, and 18 months. Gross visual function was assessed indirectly in 18-month-old animals using the light/dark exploration test. Brains were collected for autoradiography of tau pathology and presynaptic density with [18F]Flortaucipir and [3H]UCB-J, respectively, while A{beta} plaque load was measured by immunohistochemistry. Correlation and linear mixed-effects regression analyses were used to assess relationships between behavioral and pathological measures. ResultsAPP/PS1 mice showed normal cognitive performance at 6 months, a selective long-term memory deficit at 12 months, and severe impairments in learning and retention at 18 months, independent of visual confounds. Age-dependent increases in [18F]Flortaucipir binding and A{beta} plaque load were observed in all brain regions of TG compared to WT mice, whereas [3H]UCB-J binding was increased in a region-dependent manner in 18-month-old TG vs. WT animals. Barnes maze performance during the final day of testing correlated negatively with both A{beta} and tau pathology across all areas examined. Linear regression revealed a significant association between tau and age and between tau and A{beta} in the cortex, indicating that memory decline in ageing TG mice was driven by the combined effects of these pathologies. ConclusionsDeficits in memory retention precede impairments in task learning performance in APP/PS1 mice. Spontaneous tau accumulation contributes to the progressive cognitive decline, capturing key aspects of the A{beta}-tau interaction observed in human AD.

neuroscience↗

bioRxiv2024

Control of alveolar bone development, homeostasis, and socket healing by salt inducible kinases

Alveolar bone supports and anchors teeth. The parathyroid hormone-related protein (PTHrP) pathway plays a key role in alveolar bone biology. Salt inducible kinases (SIKs) are important downstream regulators of PTH/PTHrP signaling in the appendicular skeleton where SIK inhibition increases bone formation and trabecular bone mass. However, the function of these kinases in alveolar bone remains unknown. Here, we report a critical role for SIK2/SIK3 in alveolar bone development, homeostasis, and socket healing after tooth extraction. Inducible SIK2/SIK3 deletion led to dramatic alveolar bone defects without changes in tooth eruption. Ablating these kinases impairs alveolar bone formation due to disrupted osteoblast maturation, a finding associated with ectopic periostin expression by fibrous cells in regions of absent alveolar bone at steady state and following molar extraction. Distinct phenotypic consequences of SIK2/SIK3 deletion in appendicular versus craniofacial bones prompted us to identify a specific transcriptomic signature in alveolar versus long bone osteoblasts. Thus, SIK2/SIK3 deletion illuminates a key role for these kinases in alveolar bone biology and highlights the emerging concept that different osteoblast subsets utilize unique genetic programs. Summary statementSIK2/SIK3 deletion in alveolar bone reduces bone formation and mass by impairing osteoblast maturation, unlike in long bones, where it increases bone formation and mass.

developmental biology↗

bioRxiv2022

Sustained morphine delivery suppresses bone formation and alters metabolic and circulating miRNA profiles in male C57BL/6J mice

Opioid use is detrimental to bone health, causing both indirect and direct effects on bone turnover. While the mechanisms of these effects are not entirely clear, recent studies have linked chronic opioid use to alterations in circulating miRNAs. Our aim was to develop a model of opioid-induced bone loss to understand bone turnover and identify candidate miRNA-mediated regulatory mechanisms. We evaluated the effects of sustained morphine treatment on the skeleton, metabolism, and body composition of male and female C57BL/6J mice by treating with vehicle (0.9% saline) or morphine (18 mg/kg) using subcutaneous osmotic minipumps for 25 days. Morphine-treated mice had higher energy expenditure and respiratory quotient, indicating a shift toward carbohydrate metabolism. Microcomputed tomography ({micro}CT) analysis indicated that male mice treated with morphine had reduced trabecular bone volume fraction (Tb.BV/TV) (15%) and Tb. bone mineral density (BMD) (14%) in the distal femur compared to vehicle. Conversely, bone microarchitecture was not changed in females after morphine treatment. Histomorphometric analysis demonstrated that in males, morphine reduced bone formation rate compared to vehicle, but osteoclast parameters were not different. Furthermore, morphine reduced bone formation marker gene expression in the tibia of males (Bglap and Dmp1). Circulating miRNA profile changes were evident in males, with 14 differentially expressed miRNAs associated with morphine treatment. Target analysis indicated hypoxia inducible factor (HIF) signaling pathway was targeted by miR-223-3p and fatty acid metabolism by miR-484, - 223-3p, and -328-3p. In summary, we have established a model where morphine leads to a lower trabecular bone formation in males. Further, understanding the mechanisms of bone loss from opioid treatment will be important for improving management of the adverse effects of opioids on the skeleton.

physiology↗

bioRxiv2021

In vivo evidence that SORL1, encoding the endosomal recycling receptor SORLA, can function as a causal gene in Alzheimer's Disease

The few established causal genes in Alzheimers disease (AD), mutations in APP and PSENs, have been functionally characterized using biomarkers, capturing an in vivo profile reflecting the diseases initial preclinical phase. SORL1, a gene encoding the endosome recycling receptor SORLA, epidemiologically behaves as a causal gene when truncating mutations lead to partial loss of protein function. Here, in an effort to test whether SORL1 can indeed function as an AD causal gene, we used CRISPR-Cas9-based gene editing to develop a novel model of SORL1 haploinsufficiency in Gottingen Minipigs taking advantage of porcine models for biomarker investigations. SORL1 haploinsufficiency in young minipigs was found to phenocopy the preclinical in vivo profile of AD observed with other causal genes, resulting in spinal fluid abnormalities in A{beta} and tau, with no evident neurodegeneration or amyloid plaque formation. These studies provide functional support that SORL1 is a bona fide causal gene in AD, and when taken together with recent insight on other AD-causal genes, support the idea that dysfunctional endosomal recycling is a dominant pathogenic pathway in the disease.

neuroscience↗

bioRxiv2021

Control of osteocyte dendrite formation by Sp7 and its target gene osteocrin

Osteocytes use an elaborate network of dendritic connections to control bone remodeling. Some osteoblasts embed within mineralized bone matrix, change shape, and become osteocytes. The molecular circuitry that drives dendrite formation during "osteocytogenesis" is poorly understood. Here we show that deletion of Sp7, a gene linked to rare and common skeletal disease, in mature osteoblasts and osteocytes causes severe defects in osteocyte dendrites. Unbiased profiling of Sp7 target genes and binding sites reveals unexpected repurposing of this transcription factor to drive dendrite formation. Osteocrin is a Sp7 target gene that promotes osteocyte dendrite formation and rescues phenotypic and molecular defects in Sp7-deficient mice. Single-cell RNA-sequencing demonstrates overt defects in osteocyte maturation in vivo in the absence of Sp7. Sp7-dependent gene networks enriched in developing osteocytes are associated with rare and common human skeletal traits. Moreover, humans homozygous for the osteogenesis imperfecta-causing SP7R316C mutation show dramatic defects in osteocyte morphology. Genes that mark osteocytes in vivo and that are regulated by Sp7 in vitro are highly enriched in neurons, highlighting shared features between osteocytic and neuronal connectivity. Taken together, these findings reveal a crucial role for Sp7 and its target gene Osteocrin in osteocytogenesis, demonstrating that pathways that control osteocyte development influence human bone diseases.

molecular biology↗

bioRxiv2021

Dual targeting of salt inducible kinases and CSF1R uncouples bone formation and bone resorption

Bone formation and resorption are typically coupled, such that the efficacy of anabolic osteoporosis treatments may be limited by bone destruction. The multi-kinase inhibitor YKL-05-099 potently inhibits salt inducible kinases (SIKs) and may represent a promising new class of bone anabolic agents. Here we report that YKL-05-099 increases bone formation in hypogonadal female mice without increasing bone resorption. Postnatal mice with inducible, global deletion of SIK2 and SIK3 show increased bone mass, increased bone formation, and, distinct from the effects of YKL-05-099, increased bone resorption. No cell-intrinsic role of SIKs in osteoclasts was noted. In addition to blocking SIKs, YKL-05-099 also binds and inhibits CSF1R, the receptor for the osteoclastogenic cytokine M-CSF. Modeling reveals that YKL-05-099 binds to SIK2 and CSF1R in a similar manner. Dual targeting of SIK2/3 and CSF1R induces bone formation without concomitantly increasing bone resorption and thereby may overcome limitations of most current anabolic osteoporosis therapies.

physiology↗

bioRxiv2020

Systems genetics analyses in Diversity Outbred mice inform human bone mineral density GWAS and identify Qsox1 as a novel determinant of bone strength

Genome-wide association studies (GWASs) for osteoporotic traits have identified over 1000 associations; however, their impact has been limited by the difficulties of causal gene identification and a strict focus on bone mineral density (BMD). Here, we used Diversity Outbred (DO) mice to directly address these limitations by performing the first systems genetics analysis of 55 complex skeletal phenotypes. We applied a network approach to cortical bone RNA-seq data to discover 72 genes likely to be causal for human BMD GWAS associations, including the novel genes SERTAD4 and GLT8D2. We also performed GWAS in the DO for a wide-range of bone traits and identified Qsox1 as a novel gene influencing cortical bone accrual and bone strength. Our results provide a new perspective on the genetics of osteoporosis and highlight the ability of the mouse to inform human genetics.

genetics↗

bioRxiv2020

Trpm8 modulates thermogenesis in a sex-dependent manner without influencing cold-induced bone loss

Trpm8 (transient receptor potential cation channel, subfamily M, member 8) is expressed by sensory neurons, and it is involved in the detection of cold temperatures. Increased TRPM8 activity triggers an increase in uncoupling protein 1 (Ucp1)-dependent brown adipose tissue (BAT) thermogenesis. Bone density and marrow adipose tissue are regulated by rodent housing temperature and brown adipose tissue, suggesting one mediator of this effect may be TRPM8. In order to test whether TRPM8 was involved in the co-regulation of thermogenesis and bone homeostasis, we examined the bone phenotypes of one-year-old Trpm8 knockout mice (Trpm8-KO) and then exposed them to a 4-week cold temperature challenge. Male Trpm8-KO mice had lower bone mineral density than WT, with smaller bone size (femur length and cross-sectional area) being the most striking finding, and exhibited a delayed cold acclimation with increased BAT expression of Ucp1, Dio2 and Cidea at the end of the study. In contrast to males, female Trpm8-KO mice had low vertebral bone microarchitectural parameters, but no genotype-specific alterations in body temperature. Interestingly, Trpm8 was not required for cold-induced trabecular bone loss in either sex, but may be required for cold-induced changes in marrow adiposity in males. Furthermore, bone marrow adipose tissue accumulation in females was significantly blunted by Trpm8 deletion. In summary, we identified sex differences in the role of TRPM8 in maintaining body temperature, bone density and marrow adipose tissue. Identifying mechanisms through which cold temperature and brown adipose tissue influence bone could help to ameliorate potential bone side effects of obesity treatments designed to stimulate thermogenesis.

physiology↗

bioRxiv2020

Propranolol and parathyroid hormone synergistically improve bone volume fraction by suppressing resorption

Although the non-selective {beta}-blocker, propranolol, improves bone density with PTH treatment in mice, the mechanism of this effect is unclear. To address this, we used a combination of in vitro and in vivo approaches to address how propranolol influences bone remodeling in the context of PTH treatment. In female C57BL/6J mice, intermittent PTH and propranolol had complementary effects in the trabecular bone of the distal femur and L5 vertebra, with combination treatment achieving micro-architectural parameters beyond that of PTH alone. Combined treatment improved the serum bone formation marker, P1NP, but did not impact other histomorphometric parameters relating to osteoblast function at the L5. In vitro, propranolol amplified the acute, PTH-induced, intracellular calcium signal in osteoblast-like cells. The most striking finding, however, was suppression of PTH-induced bone resorption. Despite this, PTH-induced receptor activator of nuclear factor kappa-B ligand (RANKL) mRNA and protein levels were unaltered by propranolol, which led us to hypothesize that propranolol could act directly on osteoclasts. Using in situ methods, we found Adrb2 expression in osteoclasts in vivo, suggesting {beta}-blockers may directly impact osteoclasts. Taken together, this work suggests a strong anti-osteoclastic effect of non-selective {beta}-blockers in vivo, indicating that combining propranolol with PTH could be beneficial to patients with extremely low bone density.

physiology↗

bioRxiv2018

Dynamic 11C-PiB PET shows cerebrospinal fluid flow alterations in Alzheimer’s disease and multiple sclerosis

Cerebrospinal fluid (CSF) plays an important role in the clearance of solutes and maintenance of brain homeostasis. 11C-PiB PET was recently proposed as a tool for detection of CSF clearance alterations in Alzheimers disease. The current study seeks to investigate the magnitude of 11C-PiB PET signal in the lateral ventricles of an independent group of Alzheimers and mild cognitive impairment subjects. We have also evaluated multiple sclerosis as a model of disease with CSF clearance alterations without amyloid-beta tissue accumulation.\n\nMethodsA set of Alzheimers and mild cognitive impairment subjects and a set of multiple sclerosis subjects with matched healthy controls underwent MRI and dynamic 11C-PiB PET. Manual lateral ventricle regions of interest were generated from MRI data. PET data was analysed using a simplified reference tissue model with cerebellum or a supervised reference region, for the Alzheimers and multiple sclerosis datasets, respectively. Magnitude of 11C-PiB signal in the lateral ventricles was calculated as area under curve from 35 to 80 minutes and standard uptake value ratio (SUVR) from 50 to 70 minutes. Compartmental modelling analysis was performed on a separate dataset containing Alzheimers and matched healthy control data with an arterial input function to further understand the kinetics of the lateral ventricular 11C-PiB signal.\n\nResultsAnalysis of variance revealed significant group differences in lateral ventricular SUVR across the Alzheimers, mild cognitive impairment, and healthy control groups (p=0.004). Additional pairwise comparisons revealed significantly lower lateral ventricular SUVR in Alzheimers compared to healthy controls (p<0.001) and mild cognitive impairment (p=0.029). Lateral ventricular SUVR was also significantly lower in multiple sclerosis compared to healthy controls (p=0.008). Compartmental modelling analysis revealed significantly lower uptake rates of 11C-PiB signal from blood (p=0.005) and brain tissue (p=0.004) to the lateral ventricles in Alzheimers compared to healthy controls. This analysis also revealed significantly lower clearance of 11C-PiB signal out of the lateral ventricles in Alzheimers compared to healthy controls (p=0.002).\n\nConclusionOverall, these results indicate that dynamic 11C-PiB PET can be used to observe pathological changes in cerebrospinal fluid dynamics and that cerebrospinal fluid-mediated clearance is reduced in Alzheimers disease and multiple sclerosis compared to healthy controls.

neuroscience↗

bioRxiv2018

Tauopathy in the APPswe/PS1ΔE9 mouse model of familial Alzheimer’s disease

Despite compelling evidence that the accumulation of amyloid-beta (A{beta}) promotes cortical MAPT (tau) aggregation in familial and idiopathic Alzheimers disease (AD), murine models of cerebral amyloidosis are not considered to develop tau-associated pathology. The absence of neurofibrillary lesions in amyloidosis mice remains a challenge for the amyloidocentric paradigm of AD pathogenesis. It has resulted in the generation of transgenic mice harboring mutations in their tau gene, which may be inappropriate for studying a disease with no known TAU mutations, such as AD. Here, we have used APPswe/PS1{Delta}E9 mice to show that tau pathology can develop spontaneously in murine models of familial AD. Tauopathy was abundant around A{beta} deposits, with Gallyas- and thioflavin-S-positive perinuclear inclusions accumulating in the APPswe/PS1{Delta}E9 cortex by 18 months of age. Age-dependent increases in Gallyas signal correlated positively with binding levels of the paired helical filament (PHF) ligand [18F]Flortaucipir, in all brain areas examined. Sarkosyl-insoluble PHFs were visualized by electron microscopy. Tandem mass tag proteomics identified sequences of hyperphosphorylated tau in transgenic mice, along with signs of RNA missplicing, ribosomal dysregulation and disturbed energy metabolism. Human frontal gyrus tissue was used to validate these findings, revealing primarily quantitative differences between the tauopathy observed in AD patient vs. transgenic mouse tissue. Levels of tau mRNA were not different between APPswe/PS1{Delta}E9 and littermate control animals. As physiological levels of endogenous, wild-type tau aggregate secondarily to A{beta} in transgenic mice, this study demonstrates that amyloidosis is both necessary and sufficient to drive tauopathy in experimental models of familial AD.

neuroscience↗