Biology subjects

Nijsure, M. P.

Publications and source records attributed to Nijsure, M. P..

7 recordsLinked to original sources

bioRxiv2025

Local erythropoiesis directs oxygen availability in bone fracture repair

Oxygen tension dynamically regulates stem cell fate and tissue regeneration, yet how local oxygen availability is controlled within the bone marrow niche remains poorly understood. While bone marrow injury, such as by bone fracture, disrupts marrow vasculature, the consequences on local oxygen tension remain unclear. Here, we show in mice that while the tissue oxygen tension in bone marrow is low (25 mmHg, [~]4% O2), intracellular oxygenation is heterogeneous and erythroid cells are high in oxygen. Bone fracture elevates oxygen tension in the injured bone marrow (>55 mmHg, [~]8%), which persists for over a week post-injury. This oxygen elevation results not from angiogenesis, but rather from localized expansion of erythroid precursor cells in the injured bone marrow. The activated erythroid precursors synthesize hemoglobin and accumulate oxygen, acting as local modulators of oxygen tension. Blocking transferrin receptor 1 (CD71)-mediated iron uptake impairs hemoglobin synthesis, reduces local oxygen levels, and enhances bone regeneration through increased angiogenesis and osteogenesis. These findings identify erythroid precursors as active regulators of local oxygen availability in the bone marrow niche, which may be targetable to enhance tissue regeneration.

cell biology↗

bioRxiv2024

YAP regulates periosteal expansion in fracture repair

Bone fracture repair initiates by periosteal expansion. The periosteum is typically quiescent, but upon fracture, periosteal cells proliferate and contribute to bone fracture repair. The expansion of the periosteum is regulated by gene transcription; however, the molecular mechanisms behind periosteal expansion are unclear. Here, we show that Yes-Associated Protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) mediate periosteal expansion and periosteal cell proliferation. Bone fracture increases the number of YAP-expressing periosteal cells, and deletion of YAP and TAZ from Osterix (Osx) expressing cells impairs early periosteal expansion. Mechanistically, YAP regulates both cell-intrinsic and cell-extrinsic factors that allow for periosteal expansion. Specifically, we identified Bone Morphogenetic Protein 4 (BMP4) as a cell extrinsic factor regulated by YAP, that rescues the impairment of periosteal expansion upon YAP/TAZ deletion. Together, these data establish YAP mediated transcriptional mechanisms that induce periosteal expansion in the early stages of fracture repair and provide new putative targets for therapeutic interventions.

cell biology↗

bioRxiv2024

Learning on a Limb: An outreach module to engage high school students in orthopaedics

Orthopaedic researchers need new strategies for engaging diverse students. Our field has demonstrated noticeable gaps in racial, ethnic, and gender diversity, which inhibit our ability to innovate and combat the severe socioeconomic burden of musculoskeletal disorders. Towards this goal, we designed, implemented, and evaluated Learning on a Limb, an orthopaedic research outreach module to teach diverse high school students about orthopaedic research. During the 4-hr module, students completed hands-on activities to learn how biomechanical testing, microcomputed tomography, cell culture, and histology are used in orthopaedic research. Over three years, we recruited 32 high school students from the Greater Philadelphia Area to participate in Learning on a Limb. Most participants identified as racial/ethnic or gender minorities in orthopaedic research. Using pre/post-tests, we found that students experienced significant learning gains of 51 percentage points from completing Learning on a Limb. In addition to teaching students about orthopaedic research, post-survey data demonstrated that participating in Learning on a Limb strongly influenced students interest in orthopaedic research. Several students acted on this interest by completing summer research experiences in the McKay Orthopaedic Research Laboratory at the University of Pennsylvania. Learning on a Limb instructors also benefited by having the opportunity to "pay it forward" to the next generation of students and build community within their department. Empowering institutions to host modules like Learning on a Limb would synergistically inspire diverse high school students and strengthen community within orthopaedic departments to ultimately enhance orthopaedic research innovations.

scientific communication and education↗

bioRxiv2023

YAP and TAZ couple osteoblast precursor mobilization to angiogenesis and mechanoregulated bone development

Endochondral ossification requires coordinated mobilization of osteoblast precursors with blood vessels. During adult bone homeostasis, vessel adjacent osteoblast precursors respond to and are maintained by mechanical stimuli; however, the mechanisms by which these cells mobilize and respond to mechanical cues during embryonic development are unknown. Previously, we found that deletion of the mechanoresponsive transcriptional regulators, YAP and TAZ, from Osterix-expressing osteoblast precursors and their progeny caused perinatal lethality. Here, we show that embryonic YAP/TAZ signaling couples vessel-associated osteoblast precursor mobilization to angiogenesis in developing long bones. Osterix-conditional YAP/TAZ deletion impaired endochondral ossification in the primary ossification center but not intramembranous osteogenesis in the bone collar. Single-cell RNA sequencing revealed YAP/TAZ regulation of the angiogenic chemokine, Cxcl12, which was expressed uniquely in vessel-associated osteoblast precursors. YAP/TAZ signaling spatially coupled osteoblast precursors to blood vessels and regulated vascular morphogenesis and vessel barrier function. Further, YAP/TAZ signaling regulated vascular loop morphogenesis at the chondro-osseous junction to control hypertrophic growth plate remodeling. In human cells, mesenchymal stromal cell co-culture promoted 3D vascular network formation, which was impaired by stromal cell YAP/TAZ depletion, but rescued by recombinant CXCL12 treatment. Lastly, YAP and TAZ mediated mechanotransduction for load-induced osteogenesis in embryonic bone.

developmental biology↗

bioRxiv2022

Mechano-epigenetic regulation of extracellular matrix homeostasis via Yap and Taz

Cells integrate mechanical cues to direct fate specification to maintain tissue function and homeostasis. While disruption of these cues is known to lead to aberrant cell behavior and chronic diseases, such as tendinopathies, the underlying mechanisms by which mechanical signals maintain cell function is not well understood. Here, we show using a novel model of tendon de-tensioning that loss of tensile cues in vivo acutely changes nuclear morphology, positioning, and expression of catabolic gene programs. Using paired ATAC/RNAseq, we further identify that a loss of cellular tension rapidly reduces chromatin accessibility in the vicinity of Yap/Taz genomic targets while also increasing expression of genes involved in matrix catabolism. Overexpression of Yap results in a reduction of chromatin accessibility at matrix catabolic gene loci, while also reducing transcriptional levels. Concordantly, depletion of Yap/Taz elevates matrix catabolic expression. Finally, we demonstrate that overexpression of Yap not only prevents the induction of a broad catabolic program following a loss of cellular tension, but also preserves the underlying chromatin state from force-induced alterations. Taken together, these results provide novel mechanistic details by which mechanical signals regulate tendon cell function to preserve matrix homeostasis through a Yap/Taz axis. Significance StatementCells integrate mechanical signals to regulate biological outputs within tissues. These processes are required for tissue function and homeostasis. Here, we show how mechanical cues (e.g. tension) directs tendon cell function and fate at a transcriptional and epigenetic level. Furthermore, we show that disruption of these mechanical cues leads to a disease-like cell state, indicating these mechanosensitive pathways could be important for diseases driven by perturbed mechanical signaling, such as tendinopathy. Finally, we demonstrate that genetic perturbation of a single protein can preserve cell and chromatin state following a loss of tension, supporting novel avenues for the development of innovative mechano-therapeutics.

cell biology↗

bioRxiv2021

Discovery of small molecule pathway regulators by image profile matching

Identifying chemical regulators of biological pathways is a time-consuming bottleneck in developing therapeutics and research compounds. Typically, thousands to millions of candidate small molecules are tested in target-based biochemical screens or phenotypic cell-based screens, both expensive experiments customized to each disease. Here, our uncustomized, virtual profile-based screening approach instead identifies compounds that match to pathways based on phenotypic information in public cell image data, created using the Cell Painting assay. Our straightforward correlation-based computational strategy retrospectively uncovered the expected, known small molecule regulators for 32% of positive-control gene queries. In prospective, discovery mode, we efficiently identified new compounds related to three query genes, and validated them in subsequent gene-relevant assays, including compounds that phenocopy or pheno-oppose YAP1 overexpression and kill a Yap1-dependent sarcoma cell line. This image profile-based approach could replace many customized labor- and resource-intensive screens and accelerate the discovery of biologically and therapeutically useful compounds. One sentence summaryIf a genetic perturbation impacts cell morphology, a computational query can reveal compounds whose morphology "matches".

bioinformatics↗

bioRxiv2020

YAP and TAZ promote periosteal osteoblast precursor expansion and differentiation for fracture repair

In response to bone fracture, periosteal progenitor cells proliferate, expand, and differentiate to form cartilage and bone in the fracture callus. These cellular functions require the coordinated activation of multiple transcriptional programs, and the transcriptional regulators Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) regulate osteochondroprogenitor activation during endochondral bone development. However, recent observations raise important distinctions between the signaling mechanisms used to control bone morphogenesis and repair. Here, we tested the hypothesis that YAP and TAZ regulate osteochondroprogenitor activation during endochondral bone fracture healing. Constitutive YAP and/or TAZ deletion from Osterix-expressing cells impaired both cartilage callus formation and subsequent mineralization. However, this could be explained either by direct defects in osteochondroprogenitor differentiation after fracture, or by developmental deficiencies in the progenitor cell pool prior to fracture. Consistent with the second possibility, we found that developmental YAP/TAZ deletion produced long bones with impaired periosteal thickness and cellularity. Therefore, to remove the contributions of developmental history, we next generated adult onset-inducible knockout mice (using Osx1-CretetOff) in which YAP and TAZ were deleted prior to fracture, but after normal development. Adult onset-induced YAP/TAZ deletion had no effect on cartilaginous callus formation, but impaired bone formation at 14 days post-fracture (dpf). Earlier, at 4 dpf, adult onset-induced YAP/TAZ deletion impaired the proliferation and expansion of osteoblast precursor cells located in the shoulder of the callus. Further, activated periosteal cells isolated from this region at 4 dpf exhibited impaired osteogenic differentiation in vitro upon YAP/TAZ deletion. Finally, confirming the effects on osteoblast function in vivo, adult onset-induced YAP/TAZ deletion impaired bone formation in the callus shoulder at 7 dpf, prior to the initiation of endochondral ossification. Together, these data show that YAP and TAZ promote the expansion and differentiation of periosteal osteoblast precursors to accelerate bone fracture healing.

developmental biology↗