Biology subjects

Mazur, C. M.

Publications and source records attributed to Mazur, C. M..

6 recordsLinked to original sources

bioRxiv2026

Fibroblast Growth Factor Receptor Signaling in Maturing Osteoblasts Controls Cell-Matrix Interactions Critical for Osteocyte Survival

The terminal differentiation of osteoblasts into osteocytes, the most abundant cell type in cortical bone, is critical for skeletal homeostasis. Osteocyte loss is a hallmark of bone aging and fragility, yet the mechanisms regulating osteocyte formation and survival are poorly understood. We show that inactivation of fibroblast growth factor receptor 1 (Fgfr1) in the mature osteoblast lineage results in extensive osteocyte death, identifying FGFR1 signaling as essential for osteocyte viability and bone integrity. Lineage tracing and analysis of endogenous and induced appositional bone formation revealed that newly embedded osteocytes fail to survive without FGFR1. These osteocytes exhibited ectopic expression of osteocalcin and podoplanin within sclerostin-positive, TUNEL-reactive lacunae, along with defective dendrite formation and disruption of the local lacunocanalicular network. RNA sequencing of cortical bone demonstrated reduced expression of extracellular matrix (ECM) genes and neuronal regulatory genes, while histological and ultrastructural analyses showed disorganized collagen fibrils, diminished osteoid, and abnormal mineralization. In vitro, FGF signaling in Ocy454 cells regulated gene programs involved in development, axon guidance, and bone ECM organization, highlighting a dual function for FGF signaling in which it controls both matrix-dependent and intrinsic cell differentiation mechanisms during the osteoblast-to-osteocyte transition. We propose that FGFR1 deficiency causes ECM disorganization and impaired dendrite formation, disrupting osteocyte communication with neighboring bone and vascular cells, ultimately leading to cell death. These findings establish FGFR signaling as a critical regulator of osteocyte differentiation, viability of bone-embedded osteocytes, and bone homeostasis. Summary StatementFGFR signaling has a profound effect on adult bone extracellular matrix that is vital to maintaining the viability and morphology of newly formed osteocytes, their lacunocanalicular network and the maintenance of bone homeostasis.

developmental biology↗

bioRxiv2025

Genome-wide CRISPR interference screen identifies Clip2 as a novel regulator of osteocyte maturation and morphology

Osteocytes play critical roles in bone, making them attractive targets for therapeutics to improve bone mass and strength. The genes driving osteocyte maturation and function are not fully understood. Here we aimed to identify novel genes responsible for osteocyte differentiation and dendrite development by performing a genome-wide CRISPR-interference (CRISPRi) screen in the Ocy454 osteocyte-like cell line. We identify CD61 (integrin {beta}3) as a marker of osteocyte maturation: surface CD61 expression increases during osteocyte maturation, and CD61high cells express higher levels of osteocyte marker genes. We then developed a flow cytometry-based assay to quantify surface CD61 protein levels as a phenotypic endpoint for functional genomic screening. In a genome-wide screen, we identified Clip2, which encodes a microtubule binding protein, as one of dozens of genes necessary for CD61 expression. Clip2 inhibition decreased surface CD61 expression, reduced expression of osteocyte-specific genes Dmp1 and Sost, and impaired dendrite morphology in vitro. Together, these results highlight the utility of surface CD61 as a marker of osteocyte maturity and identify a role of the microtubule cytoskeleton for osteocyte differentiation, form, and function.

cell biology↗

bioRxiv2024

Trafficking and translation of mRNA in osteocyte dendrites

Osteocyte dendrites extend great distances through canaliculi in bone supported by an extensive cytoskeletal network. The formation and maintenance of osteocyte dendrites is closely linked to bone health, yet the mechanisms regulating these processes are poorly understood. Here we tested the hypothesis that osteocytes transport mRNA to their dendrites for local translation as a mechanism of regulating the formation and maintenance of these subcellular structures. Using molecular and imaging approaches, we demonstrated that a subset of mRNAs are enriched in Ocy454 osteocyte-like cell dendrites. To understand how certain mRNAs are directed to dendrites, we performed a massively parallel reporter assay with 7115 oligonucleotide sequences designed from the 3 untranslated regions of eight dendrite-enriched transcripts. We identified localization sequences within some 3UTRs that were both sufficient and necessary for trafficking to osteocyte dendrites, indicating that localization directions are specifically encoded in enriched transcripts. Furthermore, we found that dendrites contain the elements necessary for local translation, and trafficked transcripts were engaged in active translation within dendrites. Together this work describes a molecular regulatory mechanism novel to osteocyte biology with many potential consequences for the spatiotemporal control of the cytoskeleton and dendrites.

molecular biology↗

bioRxiv2021

Partial prevention of glucocorticoid-induced osteocyte deterioration with osteocrin gene therapy

Glucocorticoid (GC)-induced osteoporosis and subsequent bone fragility are preceded by death and dysfunction at the cellular level. In particular, short-term glucocorticoid excess suppresses osteocyte remodeling of the surrounding bone mineral, causes apoptosis of osteoblasts and osteocytes, and disrupts homeostatic bone remodeling. Preventing apoptosis and preserving osteocyte morphology and function could be effective means of preventing bone loss during glucocorticoid excess. We hypothesized that osteocrin, which preserves osteocyte viability and morphology in other models where osteocyte defects exist, could prevent osteocyte death and dysfunction in a GC excess model. We used a liver-targeted adeno-associated virus (AAV8) to induce osteocrin overexpression in mice one week prior to implantation with prednisolone or placebo pellets. After 28 days, tissues were collected for micro-CT and histological analysis. GC excess caused the expected reduction in cortical bone thickness and osteocyte canalicular length in control AAV8-treated mice, and these effects were blunted in mice overexpressing osteocrin. However, GC-induced changes in cortical porosity, trabecular bone mass, and gene expression were not prevented by osteocrin. While the mechanism of osteocrins effects on osteocyte morphology warrants further investigation, this study does not support a role for this model of osteocrin supplementation to combat the full skeletal effects of GC excess.

physiology↗

bioRxiv2019

TGFβ regulation of perilacunar/canalicular remodeling is sexually dimorphic

1.Bone fragility is the product of defects in bone mass and bone quality, both of which show sex-specific differences. Despite this, the cellular and molecular mechanisms underpinning the sexually dimorphic control of bone quality remain unclear, limiting our ability to effectively prevent fractures, especially in postmenopausal osteoporosis. Recently, using male mice, we found that systemic or osteocyte-intrinsic inhibition of TGF{beta} signaling, achieved using the 9.6-kb DMP1 promoter-driven Cre recombinase (T{beta}RIIocy-/- mice), suppresses osteocyte perilacunar/canalicular remodeling (PLR) and compromises bone quality. Since systemic TGF{beta} inhibition more robustly increases bone mass in female than male mice, we postulated that sex-specific differences in bone quality could likewise result, in part, from dimorphic regulation of PLR by TGF{beta}. Moreover, since lactation induces PLR, we examined the effect of TGF{beta} inhibition on the female skeleton during lactation. In contrast to males, female mice that possess an osteocyte-intrinsic defect in TGF{beta} signaling were protected from TGF{beta}-dependent defects in PLR and bone quality. The expression of requisite PLR enzymes, the lacuno-canalicular network, and the flexural strength of female T{beta}RIIocy-/- bone was intact. With lactation, however, bone loss, and induction in PLR and osteocytic parathyroid hormone type I receptor (PTHR1) expression, were suppressed in T{beta}RIIocy-/- bone, relative to wild-type. Indeed, differential control of PTHR1 expression, by TGF{beta} and other factors, may contribute to dimorphism in PLR regulation in male and female T{beta}RIIocy-/- mice. These findings provide key insights into the sex-based differences in osteocyte PLR that underlie bone quality and highlight TGF{beta} signaling as a crucial regulator of lactation-induced PLR.

molecular biology↗

bioRxiv2019

Suppressed Osteocyte Perilacunar / Canalicular RemodelingPlays a Causal Role in Osteoarthritis

Osteoarthritis (OA), long considered a primary disorder of articular cartilage, is commonly associated with subchondral bone sclerosis. However, the cellular mechanisms responsible for changes to subchondral bone in OA, and the extent to which these changes are drivers of or a secondary reaction to cartilage degeneration, remain unclear. In knee joints from human patients with end-stage OA, we found evidence of profound defects in osteocyte function. Suppression of osteocyte perilacunar/canalicular remodeling (PLR) was most severe in OA subchondral bone, with lower protease expression, diminished canalicular networks, and disorganized and hypermineralized extracellular matrix. To determine if PLR suppression plays a causal role in OA, we ablated the PLR enzyme MMP13 in osteocytes, while leaving chondrocytic MMP13 intact. Not only did osteocytic MMP13 deficiency suppress PLR in cortical and subchondral bone, but it also compromised cartilage. Even in the absence of injury, this osteocyte-intrinsic PLR defect was sufficient to reduce cartilage proteoglycan content and increase the incidence of cartilage lesions, consistent with early OA. Thus, in humans and mice, osteocyte PLR is a critical regulator of cartilage homeostasis. Together, these findings implicate osteocytes in bone-cartilage crosstalk in the joint and identify the causal role of suppressed perilacunar/canalicular remodeling in osteoarthritis.

physiology↗