Biology subjects

Savendahl, L.

Publications and source records attributed to Savendahl, L..

4 recordsLinked to original sources

bioRxiv2026

Acute activation of autophagy enables growth plate regeneration following radiation-induced injury.

Purpose Radiation injury to growth plates commonly leads to skeletal late complications including short stature, limb length-discrepancy, and scoliosis/kyphosis in pediatric oncology patients. We aimed to understand the acute responses of direct growth plate irradiation that result in skeletal late complications. Materials and methods We first established an in vivo model of focal growth plate irradiation that recapitulates the clinical development of skeletal late complications and used it to explore the responses of growth plate chondrocytes within the first 72 hours of radiation exposure. To monitor acute effects of radiation exposure on human chondrocytes, rare human growth plate biopsies were exposed to ionizing radiation ex vivo. Using these approaches, we applied clonal genetic tracing and immunofluorescence to monitor changes at the cellular and molecular levels. Functional in vivo perturbations were conducted with clinically-relevant autophagy inhibitor, hydroxychloroquine. Results Growth plate irradiation disrupted the continuous production of chondrocytes required for bone elongation and was associated with DNA damage throughout the growth plate. Indicators of growth plate activity, SOX9 and the phosphorylated form of ribosomal protein S6, decreased during a 6- and 24-hour post-irradiation window but returned to normal levels 72 hours after irradiation. We identified a surge in autophagic flux throughout the growth plate during this window, based on temporal SQSTM1 and LAMP1 protein levels. The earliest stages of these response mechanisms are conserved between species and relevant to humans. Hydroxychloroquine treatment immediately after radiation injury in mice impaired growth plate regeneration, resulting in more severe late complications. Conclusion Our findings demonstrate that autophagy is an important acute response to irradiation in growth plate chondrocytes, revealing a novel potential therapeutic target for preventing radiation-induced skeletal late complications.

molecular biology↗

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

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↗

bioRxiv2025

Human growth plates house resting zone sub-populations with features of quiescent stem cells

Incomplete mapping of gene expression within human (epiphyseal) growth plates contributes to the challenges of diagnosing and treating patients with skeletal growth disorders. To address this issue, we applied spatially resolved transcriptomics to rare growth plate biopsies obtained from healthy adolescents. In addition to identifying novel markers of each zone of the human growth plate, spatial profiling revealed that the expression of genes associated with poorly understood growth disorders, including NKX3-2, SGMS2 and WNK4, is restricted to specific human growth plate zones. By elaborating on the low transcriptional activity of resting zone chondrocytes, we found that a subset of these cells exists in a functionally quiescent state in vivo, as determined by their predominantly nuclear mRNA, abundant heterochromatin, and ability to exit the G0 phase under specific conditions - features shared with skeletal stem cells in mouse growth plates. Additionally, we identified distinct and overlapping sub-populations of human resting zone chondrocytes; an exploration of their hierarchy determined that CHRDL2 and/or SFRP5-positive sub-populations are among the least quiescent resting zone cells. In summary, we generated the most comprehensive gene expression characterization of the human growth plate, which revealed novel zone-specific markers, new primary growth disorders, candidate pharmacological targets, and led us to uncover sub-populations of resting zone chondrocytes with features of quiescent stem cells. These results contribute to a better understanding of the cellular and molecular mechanisms governing human height and can facilitate improved diagnosis and treatment strategies of patients with skeletal growth disorders.

molecular biology↗