Biology subjects

Chagin, A. S.

Publications and source records attributed to Chagin, A. S..

4 recordsLinked to original sources

bioRxiv2025

Quantitative Multicolored Deep Imaging of Human Bones Reveals a Composite Osteo-Sinusoidal Niche for Mesenchymal Stromal Cells.

Human bone marrow mesenchymal stromal/stem cells (BM-MSCs) are widely utilized in clinical trials and tissue engineering; however, their native microenvironment remains poorly understood. Here, we introduced a tissue-clearing protocol for human bones and integrated it with simultaneous mRNA and protein detection. Using this protocol, named DeepBone, we spatially mapped BM-MSCs relative to key bone microenvironment components, including human blood capillaries, adipocytes, sinusoids, and bony trabeculae. Quantitative analysis revealed that the native microenvironment of human BM-MSCs in young bone is enriched in vasculature, sinusoids, bone matrix, and adipocytes. In contrast, in aged bone, BM-MSCs showed no preferential association with bone or adipocytes. Proliferative BM-MSCs were predominantly found along blood vessels. Moreover, we identified a specialized microenvironment for BM-MCs in young bone, characterized by sinusoids coiled around trabeculae and enriched by R-type vessels. These findings provide novel insights into the native niches of BM-MSCs, offering a foundation for the development of tissue-engineering strategies that mimic their physiological context.

cell biology↗

bioRxiv2025

Disrupted bone microenvironment and immune recovery following total body irradiation in a murine model

Irradiation is an effective therapy for killing cancer cells and a critical preparative regimen for hematopoietic stem cell transplantation (HSCT). However, irradiation causes side effects on healthy tissue, disrupting bone tissue and bone marrow homeostasis and leading to skeletal and immune dysfunction. To investigate these effects, we utilized a female murine model to examine the mechanisms underlying skeletal damage caused by total body irradiation. Experiments were conducted over a 12-week period of total body irradiation and HSCT, complemented by an acute study involving only total body irradiation. Irradiation led to a transient depletion of bone marrow immune cells, followed by a late increased bone marrow cellularity 12 weeks after irradiation and HSCT compared to naive, indicative of late-stage local immune induction. Cortical and trabecular bone damage emerged two weeks post-irradiation and HSCT and persisted throughout the study. This bone damage was accompanied by a sustained increase in bone marrow adiposity. Accumulation of apoptotic cells was observed in the bone marrow within six hours post-irradiation and persisted up to 12 weeks post-irradiation and HSCT. Accompanied by elevated local expression of the pro-apoptotic BAX gene and a gene elevated with the clearance of apoptotic cells, TGF-{beta}1. In vitro studies revealed that macrophages and pre-osteoclasts, but not fully differentiated osteoclasts, efficiently cleared apoptotic cells with an elevation of TGF-{beta}1 in culture supernatant. While the clearance of apoptotic cells and associated TGF-{beta}1 signaling were evident, their direct role in skeletal outcomes remains unclear. These findings suggest that persistent apoptotic cells contribute to impaired bone remodeling, possibly influencing osteoclast function and the bone microenvironment. Further research is warranted to explore whether targeting apoptotic cell clearance could reduce bone damage and support skeletal recovery following irradiation.

molecular biology↗

bioRxiv2025

A transcriptional atlas of the pubertal human growth plate reveals direct stimulation of cartilage stem cells by growth hormone.

The cartilaginous growth plate is a critical organ responsible for longitudinal bone growth. It remains open throughout life in mice but closes in humans after puberty. Growth hormone (GH) is a widely used therapy for children with growth retardation and open growth plates. However, it remains unclear whether GH directly targets human growth plates. Furthermore, while cartilage stem cells have recently been identified in mouse growth plates, their presence and GH responsiveness in human growth plates are unknown. To address these gaps, we characterized the cellular and molecular organization of early pubertal human growth plates using unique tissue samples obtained during growth-restricting surgeries. Our analysis identified two distinct populations of stem cells differing in cycling activity, molecular profiles, and regulatory factors. Quiescent stem cells were localized within a niche characterized by low Wnt and TGF{beta} signaling. To investigate the direct effects of GH, we developed a human growth plate explant culture system. GH directly stimulated explant growth and promoted stem cell proliferation by activating the JAK/STAT, TGF{beta}, and ERK pathways while inhibiting the AKT pathway. Notably, activation of the TGF{beta} pathway occurred in an autocrine manner. These findings provide critical new insights into human longitudinal growth and the mechanisms of GH action, with potential implications for optimizing treatments for growth disorders. One Sentence SummaryThis study reveals that growth hormone (GH) directly promotes proliferation within the human growth plate and activates TGF{beta} and ERK signaling pathways in cartilage stem cells, providing critical insights into human longitudinal growth and potential improvements in treatments for growth disorders.

cell biology↗

bioRxiv2019

Secondary ossification centers evolved to make endochondral bone growth possible under the weight-bearing demands of a terrestrial environment

Growth plate and articular cartilage constitute a single anatomical entity early in development, but later separate into two distinct structures by the secondary ossification center (SOC). The reason for such separation remains unknown. We found that evolutionarily SOC appears in animals conquering the land - amniotes. Analysis of ossification pattern in mammals with specialized extremities (whales, bats, jerboa) revealed that SOC development correlates with the extent of mechanical loads. Mathematical modelling revealed that SOC reduces mechanical stress within the growth plate. Functional experiments revealed high vulnerability of hypertrophic chondrocytes to mechanical stress and showed that SOC protects these cells from apoptosis caused by extensive loading. Atomic force microscopy showed that hypertrophic chondrocytes are the least mechanically stiff cells within the growth plate. Altogether, these findings suggest that SOC has evolved to protect the hypertrophic chondrocytes from the high mechanical stress encountered in the terrestrial environment.

evolutionary biology↗