Biology subjects

Migotsky, N.

Publications and source records attributed to Migotsky, N..

11 recordsLinked to original sources

bioRxiv2026

Bone Response to Mechanical Loading is Highly Heritable and Correlates with Osteocyte Lacunar Morphology in Genetically Diverse Mouse Strains

Skeletal loading is a key regulator of bone formation. Studies using in vivo loading of rodent bones have established many mechanical and biological factors that regulate bone response to loading. However, most studies have been performed in a small number of inbred rodent strains, and there are few data on effects of genetic background on the loading response. In the current study we employed two murine models of genetic diversity, the Diversity Outbred (DO) and their eight founder inbred strains, to assess the influence of genetic background on skeletal response to tibial loading. Loading-induced periosteal bone formation rates and formed bone volumes varied significantly among inbred mouse strains. DO mice, which each carry a unique mixture of alleles of the inbred founder strains, were more responsive to loading, on average, than the the inbred founder strains. Additionally, bone response to mechanical loading was highly heritable; broad-sense heritability for measures of periosteal formation were near or above 80%. Furthermore, osteocyte lacunar morphology correlated with loading response across inbred strains. Inbred 129S1 mice had the most elongated lacunae and exhibited the highest magnitude of response on both periosteal and endocortical surfaces. 129S1 also demonstrated a robust transcriptional response to loading, although the pathways induced by loading were largely conserved with lab-standard C57Bl/6. Together, these findings demonstrate that genetic background significantly contributes to bone response to loading and establish DO mice as a platform for discovery of genes that regulate skeletal mechanoresponsiveness.

bioengineering↗

bioRxiv2026

Protocol for 3D digital dynamic histomorphometry of bone via time-lapse registration of serial microCT scans

Serial in vivo microCT enables quantification of dynamic bone remodeling by capturing formation and resorption over time. This protocol uses Dragonfly to register pre- and post-intervention scans of rodent long bones through an intuitive drag-and-click workflow that requires no coding expertise. Rigid registration enables spatial mapping and quantification of formed, resorbed, and quiescent cortical and trabecular bone at periosteal and endosteal surfaces across multiple tibial regions, providing a non-destructive and complementary alternative to classic, fluorochrome-based dynamic histomorphometry. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=160 HEIGHT=200 SRC="FIGDIR/small/728585v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@e20e89org.highwire.dtl.DTLVardef@12872fcorg.highwire.dtl.DTLVardef@951694org.highwire.dtl.DTLVardef@1fd52f2_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2026

Combination Treatment with Sclerostin and Dkk1 Antibodies Synergizes with Tibial Loading to Stimulate Bone Formation in Aged Mice

Aging is associated with decreased bone formation and bone mass and increased fracture risk. Wnt pathway activation by mechanical loading is a potent strategy to improve bone mass, however, load-induced bone formation is diminished with aging. Neutralizing antibody (Ab) therapies targeting Wnt pathway inhibitors Sclerostin (Scl) and Dickkopf-related protein 1 (Dkk1) have proven successful in preclinical and clinical osteoporotic conditions. We asked whether treatment combining Scl-Ab and Dkk1-Ab can increase load-induced bone formation in a preclinical model of osteoporosis. Aged (22-month) C57BL/6N female mice underwent combination Scl-Ab plus Dkk1-Ab therapy (15 mg/kg each; subcutaneously; 2x/wk; saline control) for 2 weeks, concomitant with a mechanical loading regimen previously shown to induce modest bone formation in tibias of aged mice (-2200 {varepsilon}, 1200 cycles/day, 5 day/wk). Changes in bone morphology and formation were assessed by longitudinal microCT and dynamic histomorphometry, respectively. Molecular indices of bone formation and Wnt pathway activation were assessed by qPCR of cortical bone. Treatment with Scl-Ab plus Dkk1-Ab induced significant improvements in cancellous (BV/TV +50%) and cortical morphology (Ct.Th +25%) in non-loaded limbs of antibody-treated mice vs. vehicle control mice. Importantly, periosteal bone formation rate was 10-fold higher in loaded limbs of antibody versus vehicle treated mice, indicating a synergistic effect. Gene expression analysis showed that antibody treatment and loading synergistically upregulated Wnt1 expression, which may have contributed to the observed synergistic effect on bone formation. These results confirm the potent anabolic effect of combination Scl plus Dkk1 antibody treatment. Moreover, they show that antibody treatment and skeletal loading are more effective at increasing periosteal bone formation in aged mice than either treatment alone. These findings support the concept that combinatorial therapy using dual Scl and Dkk1 antibodies plus weight-bearing exercise may be an effective treatment for age-related osteoporosis.

physiology↗

bioRxiv2025

The developing tendon and enthesis are hypoxic and rely on hypoxia-inducible factor 1a (Hif1a) during postnatal development

The tendon-bone enthesis is a specialized fibrocartilaginous tissue crucial for muscle-to-bone force transmission, yet its postnatal development is not fully understood. Emerging evidence suggests hypoxia plays a pivotal role in enthesis maturation akin to its function in skeletal growth plates, with Hypoxia Inducible Factor 1 alpha (HIF-1) acting as a key regulator of cellular adaptation (e.g., cell survival, extracellular matrix (ECM) deposition). Here, we investigated the spatial and temporal dynamics of hypoxia in the murine Achilles tendon enthesis and elucidated the role of Hif1a in enthesis cell survival and ECM formation using Scleraxis-lineage conditional knockout (ScxCre; Hif1a cKO) mice. We found that while neonatal tendons rapidly resolve hypoxia after birth, the enthesis maintains a hypoxic niche through postnatal day 5, mirroring a gradient observed in growth plates. Disruption of HIF-1 in enthesis-resident cells resulted in pronounced deficits in grip strength, abnormal tendon-bone attachment morphology, disrupted calcaneal architecture, impaired mineralization, and significant ECM disorganization. Histological analyses revealed persistent cell death and loss of the characteristic fibrocartilaginous gradient in cKO entheses, including dysregulated collagen alignment. In vitro, HIF-1-deficient tendon fibroblasts exhibited blunted transcriptional responses to hypoxia, altered metabolic gene expression, and changes in ECM deposition. Collectively, our findings illuminate hypoxia as a sustained niche in the postnatal enthesis, with HIF-1 critically required for cell survival, ECM organization, and enthesis structural integrity. This work advances our understanding of enthesis biology and provides insights relevant to tendon-bone attachment disorders and regenerative strategies.

developmental biology↗

bioRxiv2025

The synovial lining macrophage layer develops in the first weeks of life in a CSF1- and TGFβ- dependent but monocyte-independent process.

Synovial joints harbor a protective lining layer, consisting of fibroblasts and macrophages, which form an epithelial-like barrier. In inflamed joints, lining macrophages regulate both early inflammatory cell influx and resolution. Despite these critical functions, it is currently unknown at what stage during development the synovial macrophage lining is established, and which signals drive this process. Here, we use a combination of genetic models and in vivo perturbations, single cell transcriptomics and imaging to delineate the process of lining formation in mice. We find that the synovial lining is immature at birth and becomes established within the first 3 weeks of life. In this window, the lining is gradually populated with macrophages that originate from fetal sources, proliferate and acquire the lining-specific transcriptional identity. In contrast, monocytes contribute only minimally to the developing lining, and their input remains limited in healthy adulthood. We identify CSF1 and TGF{beta} as key signals in this process, which also involves mechanosensing through PIEZO1. Our study thus identifies the early postnatal window as a critical period for lining macrophage development, with potential lifelong impact on joint health and disease.

immunology↗

bioRxiv2025

AMPK signaling is dysregulated in human tendinopathy and loss of AMPKα1 leads to cell, matrix and mechanical dysfunction in mouse Achilles tendon

Tendinopathy is a debilitating tendon disorder affecting millions of people, characterized by pain, swelling, and diminished biomechanical properties. While the precise mechanisms underlying tendon homeostasis remain unclear, metabolic regulation plays a critical role. In this study, we combine transcriptomic analysis of human tendinopathic samples with a conditional mouse model in which Prkaa1 (encoding AMPK1) is selectively deleted in tendon progenitors to elucidate the role of AMPK signaling in tendon homeostasis. RNA sequencing of diseased human tendons revealed downregulation of key metabolic genes, including several involved in the mitochondrial electron transport chain and AMPK signaling pathways, alongside an increase in markers associated with senescence and a secretory inflammatory profile. In parallel, mice with loss of Prkaa1 function exhibited normal postnatal development; however, by one month of age, tendons demonstrated widespread transcriptional alterations related to cell cycle regulation and ECM organization. By three months, AMPK1-deficient tendons showed significant reductions in mechanical strength and increased expression of senescence markers p21 and p16, progressing to prominent ectopic calcification with age. In vitro studies further confirmed that tendon fibroblasts lacking AMPK1 have altered ECM substrate adhesion profiles. Importantly, voluntary exercise partially rescued these deficits by enhancing ECM organization and reducing senescence marker expression. Collectively, our findings demonstrate that AMPK1 is critical for maintaining energy balance, regulating ECM remodeling, and preventing premature cellular senescence in tendon. These insights highlight AMPK signaling as a promising therapeutic target and underscore the beneficial role of exercise in mitigating tendinopathic changes.

pathology↗

bioRxiv2024

Functional Changes to Achilles Tendon and Enthesis in a Mouse Model of an Adolescent Masculine Gender-Affirming Hormone Treatment

Many transgender youth seek gender affirming care, such as puberty suppression, to prolong decision-making and to align their physical sex characteristics with their gender identity. During peripubertal growth, connective tissues such as tendon rapidly adapt to applied mechanical loads (e.g., exercise) yet if and how tendon adaptation is influenced by sex and gender affirming hormone therapy during growth remains unknown. The goal of this study was to understand the how pubertal suppression influences the structural and functional properties of the Achilles tendon using an established mouse model of transmasculine gender affirming hormone therapy. C57BL/6N female-born mice were assigned to experimental groups to mimic gender-affirming hormone therapy in human adolescents, and treatment was initiated prior to the onset of puberty (at postnatal day 26, P26). Experimental groups included controls and mice serially treated with gonadotropin release hormone analogue (GnRHa), delayed Testosterone (T), or GnRHa followed by T. We found that puberty suppression using GnRHa, with and without T, improved the overall tendon load capacity in female-born mice. Treatment with T resulted in an increase in the maximum load that tendon can withstand before failure. Additionally, we found that GnRHa, but not T, treatment resulted in a significant increase in cell density at the Achilles enthesis. NEW & NOTEWORTHYThese findings demonstrate that puberty suppression or testosterone does not negatively influence tendon structural or functional properties in a mouse model of transmasculine gender affirming care. In all treatment groups, the ability of the tendon to withstand load was significantly increased. Puberty suppression with GnRHa significantly increased enthesis cell density, suggesting an extended growth phase. These findings elucidate the effects of gender affirming care on the structural and functional properties of the tendon and enthesis.

physiology↗

bioRxiv2024

Spatial histomorphometry reveals that local peripheral nerves modulate but are not required for skeletal adaptation to applied load in mice

Mechanical loading is required for bone health and results in skeletal adaptation to optimize strength. Local nerve axons, particularly within the periosteum, may respond to load-induced biomechanical and biochemical cues. However, their role in the bone anabolic response remains controversial. We hypothesized that spatial alignment of periosteal nerves with sites of load-induced bone formation would clarify this relationship. To achieve this, we developed RadialQuant, a custom tool for spatial histomorphometry. Tibiae of control and neurectomized (sciatic/femoral nerve cut) pan-neuronal Baf53b-tdTomato reporter mice were loaded for 5-days. Bone formation and periosteal nerve axon density were then quantified simultaneously in non-decalcified sections of the mid-diaphysis using RadialQuant. In control animals, anabolic loading induced maximal periosteal bone formation at the site of peak compression, as has been reported previously. Loading did not significantly change overall periosteal nerve density. However, a trending 28% increase in periosteal axons was noted at the site of peak compression in loaded limbs. Neurectomy depleted 88% of all periosteal axons, with near-total depletion on load-responsive surfaces. Neurectomy alone also caused de novo bone formation on the lateral aspect of the mid-diaphysis. However, neurectomy did not inhibit load-induced increases in periosteal bone area, mineralizing surface, or bone formation rate. Rather, neurectomy spatially redistributed load-induced bone formation towards the lateral tibial surface with a reduction in periosteal bone formation at the posterolateral apex (-63%) and enhancement at the lateral surface (+1360%). Altogether, this contributed to comparable load-induced changes in cortical bone area fraction (+4.4% in controls; +5.4% in neurectomized). Our results show that local skeletal innervation modulates but is not required for skeletal adaptation to applied load. This supports the continued use of loading and weight-bearing exercise as an effective strategy to increase bone mass, even in patients with peripheral nerve damage or dysfunction. LAY SUMMARYMechanical loading is required for bone health and can increase new bone formation to optimize strength and reduce fractures. Increased bone formation with loading is primarily mediated by osteocytes, a specialized cell type that is embedded throughout the bone matrix. Local nerve axons, particularly within the periosteum, may also respond to load-induced biomechanical and biochemical cues and could contribute to new bone formation in response to load. However, their role in the bone anabolic response remains controversial. To address this, we studied the adaptation of bone to applied load in the presence of local periosteal nerves, and in settings where the nerves had been surgically removed. Our results show that local skeletal innervation modulates but is not required for skeletal adaptation to applied load. This supports the continued use of loading and weight-bearing exercise as an effective strategy to increase bone mass, even in patients with peripheral nerve damage or dysfunction.

physiology↗

bioRxiv2023

Multi-Scale Cortical Bone Traits Vary in Two Mouse Models of Genetic Diversity

Understanding the genetic basis of cortical bone traits can allow for the discovery of novel genes or biological pathways regulating bone health. Mice are the most widely used mammalian model for skeletal biology and allow for the quantification of traits that cant easily be evaluated in humans, such as osteocyte lacunar morphology. The goal of our study was to investigate the effect of genetic diversity on multi-scale cortical bone traits of three long bones in skeletally-mature mice. We measured bone morphology, mechanical properties, material properties, lacunar morphology, and mineral composition of mouse bones from two populations of genetic diversity. Additionally, we compared how intra-bone relationships varied in the two populations. Our first population of genetic diversity included 72 females and 72 males from the eight Inbred Founder strains used to create the Diversity Outbred (DO) population. These eight strains together span almost 90% of the genetic diversity found in mice (Mus musculus). Our second population of genetic diversity included 25 genetically unique, outbred females and 25 males from the DO population. We show that multi-scale cortical bone traits vary significantly with genetic background; heritability values range from 21% to 99% indicating genetic control of bone traits across length scales. We show for the first time that lacunar shape and number are highly heritable. Comparing the two populations of genetic diversity, we show each DO mouse does not resemble a single Inbred Founder but instead the outbred mice display hybrid phenotypes with the elimination of extreme values. Additionally, intra-bone relationships (e.g., ultimate force vs. cortical area) were mainly conserved in our two populations. Overall, this work supports future use of these genetically diverse populations to discover novel genes contributing to cortical bone traits, especially at the lacunar length scale. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=176 SRC="FIGDIR/small/543484v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@1e61c1org.highwire.dtl.DTLVardef@a3f941org.highwire.dtl.DTLVardef@1411dceorg.highwire.dtl.DTLVardef@bfc8c_HPS_FORMAT_FIGEXP M_FIG C_FIG

genomics↗

bioRxiv2022

Loading-Induced Bone Formation is Mediated by Wnt1 Induction in Osteoblast-Lineage Cells

Mechanical loading on the skeleton stimulates bone formation. Although the exact mechanism underlying this process remains unknown, a growing body of evidence indicates that the Wnt signaling pathway is necessary for the skeletal response to loading. Recently, we showed that Wnts produced by osteoblast lineage cells mediate the osteo-anabolic response to tibial loading in adult mice. Here, we report that Wnt1 specifically plays a crucial role in mediating the mechano-adaptive response to loading. Independent of loading, short-term loss of Wnt1 in the Osx-lineage resulted in decreased cortical bone area in the tibias of 5-month old mice. In females, strain-matched loading enhanced periosteal bone formation in Wnt1F/F controls, but not in Wnt1F/F; OsxCreERT2 knockouts. In males, strain-matched loading increased periosteal bone formation in both control and knockout mice; however, the periosteal relative bone formation rate was 65% lower in Wnt1 knockouts versus controls. Together, these findings show that Wnt1 supports adult bone homeostasis and mediates the bone anabolic response to mechanical loading.

cell biology↗

bioRxiv2021

Osteoblast-Specific Wnt Secretion is Required for Skeletal Homeostasis and Loading-Induced Bone Formation in Adult Mice

Wnt signaling is critical to many aspects of skeletal regulation, but the importance of Wnt ligands in adult bone homeostasis and the anabolic response to mechanical loading is not well documented. We inhibited Wnt ligand secretion in adult (5-mo) mice using a systemic (drug) and a bone-targeted (genetic) approach, and subjected them to axial tibial loading to induce lamellar bone formation. Mice treated with the porcupine inhibitor WNT974 exhibited a decrease in bone formation in non-loaded limbs as well as a 54% decline in the periosteal bone formation response to tibial loading. Similarly, within 1-2 weeks of Wls deletion in osteoblasts (Osx-CreERT2;WlsF/F mice), skeletal homeostasis was altered with decreased bone formation and increased resorption, and the anabolic response to loading was reduced 65% compared to control (WlsF/F). These findings establish a requirement for Wnt ligand secretion by osteoblasts for adult bone homeostasis and the anabolic response to mechanical loading.

genetics↗