Palmitic Acid Alters Longitudinal Bone Growth While Enhancing Matrix Maturation in an Organotypic Bone Model

Abstract

Palmitic acid (PA), the most abundant saturated fatty acid in the human body, is implicated in lipotoxicity under hyperlipidemic conditions, with potential consequences for bone metabolism. To investigate its impact on developing bone tissue, this study used 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 approach, integrating microtomographic, histochemical, ultrastructural, and gene expression analyses, was used to assess tissue architecture, matrix composition, mineralization, and molecular adaptations. PA exposure significantly reduced longitudinal femoral growth, as evidenced by decreased femoral length and tissue volume. Gene expression analysis revealed reduced expression of selected osteogenic differentiation-related markers, including RUNX2, BMP2, and SPP1. However, COL1A2 expression was upregulated, correlating with increased collagenous matrix deposition and enhanced mineralization in PA-treated groups. Alcian blue staining further suggested reduced proteoglycan-rich cartilage matrix, particularly at 200 µM PA. Additionally, PA modulated the expression of both pro-inflammatory and anti-inflammatory mediators, along with increased autophagy-associated responses, as suggested by the upregulation of autophagy-related genes and the presence of autophagosomes and autolysosomes. These findings indicate that PA does not simply exert a deleterious effect on bone tissue but rather redirects the developmental trajectory of the organotypic femur by reducing longitudinal growth while promoting collagen-rich matrix maturation and mineral compaction. This response may involve altered cartilage-associated endochondral processes, fatty-acid-driven metabolic adaptation, osteoblast/osteocyte maturation, and autophagy-associated matrix processing under lipid-enriched conditions.