Endocrine Abstracts

Introduction: Ectopic accumulation of fat in highly metabolic tissues is a hallmark in ageing, metabolic and neuromuscular diseases. The effects of ectopic accumulation of lipids in muscle include, glucose intolerance, switch of fibre types, reduced tolerance to exercise, etc. Less is known about what are the changes in the muscle niche driving this maladaptive remodelling. Here, we set to explore the role biomechanical changes (stiffness) on driving the cell-fate of human adipogenic precursors into adipocytes.

Methods: Human fibro/adipogenic progenitors (FAPs) and human pre-adipocytes (SGBS) were seeded in different stiffness (0.2 - 10⁶ kPa). We use FAPs control and from muscles with Duchenne Muscular Dystrophy/DMD (impaired remodelling). Differentiation into fibroblast was evaluated after treatment with TGF-ß1 (3d) and differentiation into adipocytes was evaluated after treatment with adipogenic media (3, 5, 10d). Collagen I, Fibronectin, a-SMA and FABP4 and PPARG (adipogenesis) were evaluated by western blot, as key differentiation markers. Further, targeted proteomic assay was done in FAPs after adding adipogenic media (1d) to assess involvement of protein kinases regulating the process of differentiation.

Results: We identified decreased cell survival in cells (SGBS and FAPs) at soft surfaces, this effect was greater in FAPs DMD. Increased levels of adipogenic markers (FABP4 and PPARG), were observed in SGBS and FAPs at stiffer surfaces. The effect of differentiation was less clear in fibrosis. Results from the proteomic analysis identified WNK1 and PRAS40 as relevant kinases involved in adipogenic differentiation.

Conclusions: Our results suggest higher tissue stiffness (muscle and adipose tissue), common in ageing, metabolic and neuromuscular diseases, could promote ectopic accumulation of fat by increasing the adipogenic commitment on FAPs and pre-adipocytes. The identification of targets such as, WNK1 and PRAS40 will allow us to further dissect these pathways and work on strategies to tackle adipogenesis in muscle.