Palmitic acid influence on osteogenesis and bone growth in an organotypic bone model (ex vivo)

Introduction Hyperlipidemias are highly prevalent - affecting up to half of adults in developed countries. Critically, they increase the risk of cardiovascular diseases, including coronary artery disease, peripheral artery disease, cerebrovascular accidents, and aneurysms, primarily driven by pathological process of atherosclerosis. Recent evidence also implicates hyperlipidemia in bone metabolism dysregulation, contributing to unbalanced bone loss conditions, such as osteopenia and osteoporosis. Palmitic acid (PA), the most abundant saturated fatty acid in the human body, is implicated in lipotoxicity under hyperlipidemic conditions, with potential far-reaching consequences for bone metabolism. Aim To elucidate the impact of PA in the bone tissue structure, cellular organization, matrix mineralization, and the expression of markers associated with bone metabolism. Methods To investigate PA impact on bone tissue, this study employs an ex vivo organotypic embryonic chick femur model, exposing femora to control (0 μM), low (50 μM), and high (200 μM) PA concentrations. A multimodal investigative approach, integrating microtomographic, histological, ultrastructural, and gene expression analyses, was used to comprehensively assess tissue architecture, cellular dynamics, and molecular adaptations. Results PA exposure significantly inhibited bone growth, evident in reduced femoral length and tissue volume. In the control group (0 μM PA), femoral length increased by approximately 0.3 mm over the culture period. Exposure to 50 μM PA resulted in a moderate reduction in length variation (0.2mm), while 200 μM PA significantly inhibited bone growth (0.1mm). Quantitative histomorphometric analysis revealed that both PA-treated groups exhibited significantly lower tissue volume (TV) compared to the control group. Despite this reduction, bone volume (BV) and the BV/TV ratio were significantly increased in the PAexposed femora. Bone mineral density (BMD) showed an upward trend in PA-treated groups, with the 200 μM PA group showing a significant increase in BMD compared to the control. Gene expression analysis revealed a downregulation of key osteogenic markers (RUNX2, BMP2, and SPP1), indicating impaired osteoblastic function. Paradoxically, collagen expression was upregulated, correlating with increased collagenous matrix deposition and enhanced mineralization in PA-treated groups. Additionally, PA triggered the expression of both pro-inflammatory (IL1B) and anti- inflammatory (IL-10) mediators, along with an elevated autophagic activity (ATG5 and SQSTM1), as indicated by the upregulation of autophagy-related genes and the accumulation of autophagosomes and autolysosomes. Conclusions While PA impairs osteogenic differentiation and bone growth, it paradoxically promotes matrix mineralization through alternative pathways driven by inflammatory signaling, antiinflammatory modulation, and autophagy. This multifaceted response underscores the importance of considering non-canonical pathways in bone remodeling under lipotoxic stress and may inform future therapeutic strategies targeting lipid-induced bone dysfunction.