Biology subjects

Muratovic, D.

Publications and source records attributed to Muratovic, D..

6 recordsLinked to original sources

bioRxiv2026

Human Osteocytes Express MHC ClassII and Act as Non-classical Antigen-Presenting Cells During Bacterial Infection

Osteocytes are the most abundant cells in bone and are increasingly recognised not only for their role in skeletal remodelling and inflammatory signalling but also for their potential involvement in immune responses. In this study, we searched available gene expression datasets of human primary osteocyte-like cells exposed acutely to Staphylococcus aureus and identified significantly induced expression of key genes related to antigen processing and presentation. We then confirmed that human bone explant-derived osteoblastic cells, representative of a mature osteoblast-pre-osteocyte stage, expressed, as expected, high cell surface levels of major histocompatibility complex (MHC) Class I but also, low basal levels of the MHC Class II family member, HLA-DR. However, confocal imaging revealed high expression of MHC Class II molecules and the peptide-loading chaperone HLA-DM within the lysosomal compartments, consistent with canonical antigen-processing machinery. Differentiation towards a mature osteocyte phenotype increased MHC Class II protein levels and maintained expression of intracellular HLA-DM. Exposure of mature osteocyte-like cells to S. aureus further up-regulated both intracellular and cell surface MHC Class II expression. Demonstrative of antigen presenting cell functionality, S. aureus-exposed osteocytes induced autologous CD4+ T cell proliferation. Furthermore, MHC Class II expression in osteocytes was detected in bone sampled from patients with periprosthetic joint infections, providing evidence that these mechanisms operate in vivo. Together, our findings reveal that human osteocytes are capable of inducible MHC Class II-associated antigen presentation in response to bacterial challenge, pointing to a novel role for osteocytes in adaptive immune surveillance within bone.

immunology↗

bioRxiv2026

Quantification of bone loss, periosteal bone formation and novel histopathological changes in a mouse implant-related Staphylococcus aureus infection model

Implant-associated bone infection involves a complex interplay between pathogenic stimuli and host cell responses, yet analysis in preclinical models has typically relied on qualitative or semi-quantitative measures. We aimed to establish a quantified evaluation framework to define host-pathogen relationships in a preclinical implant infection model. Staphylococcus aureus-coated stainless-steel implants were inserted trans-cortically in mouse tibiae and bone changes recorded longitudinally by in vivo micro-CT. An automated segmentation task list was developed to independently isolate and quantify cortical, periosteal-reactive, and trabecular bone compartments. RGB trichrome histomorphometry was used to quantify bone matrix integrity, osteocyte lacunar geometry, and osteoclastic activity. Droplet digital PCR was used to determine absolute bacterial and host genome copy number. Infected implants produced marked reductions in trabecular bone volume fraction, number, and bone mineral density (BMD), together with decreased cortical bone volume fraction and increased cortical porosity, accompanied by significant elevations in periosteal bone volume fraction. Histologically, infected bone exhibited increased eroded surface indicative of osteoclastic resorption, extensive degraded bone matrix and pathological remodelling of osteocyte lacunae towards circularity, consistent with an osteocytic osteolysis response. Infection-induced changes to cortical bone structure correlated mostly with host cell rather than bacterial load; however, cortical BMD negatively correlated with the bacterial:host genome ratio. This multifaceted, quantified framework reveals distinct pathobiological effects of implant-associated infection on trabecular, cortical, and periosteal bone compartments, bone matrix and osteocyte and osteoclast populations, consistent with reports in human patients, suggesting that major pathological changes are driven by the host bone cell response to infection.

pathology↗

bioRxiv2023

Beyond the Colony-Forming-Unit: Rapid Bacterial Evaluation in Osteomyelitis

Examination of bacteria/host cell interactions is important for understanding the aetiology of many infectious diseases. The colony-forming-unit (CFU) has been the standard for quantifying bacterial burden for the past century, however, this suffers from low sensitivity and is dependent on bacterial culturability in vitro. Our data demonstrate the discrepancy between the CFU and bacterial genome copy number in an osteomyelitis-relevant co-culture system and we confirm diagnosis and quantify bacterial load in clinical bone specimens. This study provides an improved workflow for the quantification of bacterial burden in such cases.

microbiology↗

bioRxiv2023

Microstructural and cellular characterisation of the subchondral trabecular bone in human knee and hip osteoarthritis using synchrotron tomography

ObjectiveIt is unclear if different factors influence osteoarthritis (OA) progression and the changes characterising OA disease in hip and knee. We investigated the difference between hip OA and knee OA at the subchondral bone tissue and cellular level, relative to the degree of cartilage degeneration. DesignBone samples were collected from 11 patients (aged 70{+/-}8 years) undergoing knee arthroplasty and 8 patients (aged 64{+/-}12 years) undergoing hip arthroplasty surgery. Bone microstructure, osteocyte-lacunar network and bone matrix vascularity were evaluated using synchrotron micro-CT imaging. Samples were additionally examined histologically to determine osteocyte density, viability, and connectivity. ResultsAfter adjustment for donor gender and age, associations between the extent of cartilage degeneration, bone volume fraction [8.7, 95% CI (3.4, 14.1)], trabecular number [1.5, 95% CI (0.8, 2.3)], osteocyte lacunar density [4714.9; 95% CI (2079.1, 7350.6)] and trabecular separation [-0.06, 95% CI (0.01, 0.1)] were found in both knee and hip OA. When compared to knee OA, hip OA was characterised by higher trabecular thickness [0.006, 95% CI (-4, 0.01)], larger but less spheric osteocyte lacunae [47.3; 95% CI (11.2, 83.4), -0.04; 95% CI (-0.6, -0.01), respectively], lower vascular canal density [-22.8; 95% CI (-35.4, -10.3)] lower osteocyte density [-84.9; 95% CI (-102.4, -67.4)], and less senescent but more apoptotic osteocytes [-2.4; 95% CI (-3.6, -1.2), 24.9; 95% CI (17.7, 32.1)], respectively. ConclusionSubchondral bone from hip OA and knee OA exhibits different characteristics at the tissue and cellular levels, suggesting different mechanisms of OA progression between the hip and knee joints.

pathology↗

bioRxiv2022

Hip osteoarthritis: A novel network analysis of subchondral trabecular bone structures

Hip osteoarthritis (HOA) is a degenerative joint disease that leads to the progressive destruction of subchondral bone and cartilage at the hip joint. Development of effective treatments for HOA remains an open problem, primarily due to the lack of knowledge of its pathogenesis and a typically late-stage diagnosis. We describe a novel network analysis methodology for micro-computed tomography (micro-CT) images of human trabecular bone. We explored differences between the trabecular bone microstructure of femoral heads with and without HOA. Large-scale automated extraction of the network formed by trabecular bone revealed significant network properties not previously reported for bone. Profound differences were discovered, particularly in the proximal third of the femoral head, where HOA networks demonstrated elevated numbers of edges, vertices and graph components. When further differentiating healthy joint and HOA networks, the latter showed fewer small-world network properties, due to decreased clustering coefficient and increased characteristic path length. Furthermore, we found that HOA networks had reduced length of edges, indicating the formation of compressed trabecular structures. In order to assess our network approach, we developed a deep learning model for classifying HOA and control cases, and we fed it with two separate inputs: (i) micro-CT images of the trabecular bone, and (ii) the network extracted from them. The model with plain micro-CT images achieves 74.63% overall accuracy while the trained model with extracted networks attains 96.47% accuracy. We anticipate our findings to be a starting point for a novel description of bone microstructure in HOA, by considering the phenomenon from a graph theory viewpoint.

biophysics↗

bioRxiv2021

Elevated levels of active Transforming Growth Factor β1 in the subchondral bone relate spatially to cartilage loss and impaired bone quality in human knee osteoarthritis

ObjectiveOver-activity of transforming growth factor {beta}1 (TGF{beta}1) in subchondral bone has a direct causal role in rodent models of knee osteoarthritis (OA), which can be blocked by TGF{beta}1 neutralisation. In this study, we investigated whether the spatially distributed level of active TGF{beta}1 in human subchondral bone associates with the characteristic structural, cellular and molecular parameters of human knee OA. DesignSubchondral bone samples (35 OA arthroplasty patients, aged 69{+/-}9 years) were obtained from regions below either macroscopically present or denuded cartilage. Bone samples were processed to determine the concentration of active TGF{beta}1 (ELISA) and gene-specific mRNA expression (RT-PCR). Synchrotron micro-CT imaging was utilised to assess the bone microstructure, bone mineralization, the osteocyte lacunar network and bone matrix vascularity. Finally, samples were histologically examined for cartilage OARSI grading, quantification of tartrate resistant acid phosphatase positive cells and bone marrow micro-vasculature. ResultsSubchondral bone below severely degenerated/depleted cartilage, characterised by impaired bone matrix quality due to sclerotic microarchitecture, disorganised collagen, high heterogeneity of the mineral distribution, contained increased concentrations of active TGF{beta}1, compared to adjacent areas with more intact cartilage. In addition, increased levels of active TGF{beta}1 related directly to increased bone volume while increased OARSI grade associated directly with morphometric characteristics (size, shape and orientation) of osteocyte lacunae. ConclusionThese results indicate that increased active TGF{beta}1 associates spatially with impaired bone quality and the disease severity of human OA. This study therefore suggests that TGF{beta}1 could be a therapeutic target to prevent or reduce human disease progression.

pathology↗