Lineage-Specific Mechanical Trajectories of Lipid Droplets during Late-Stage Adipocyte Differentiation

Lipid droplets (LDs) are dynamic intracellular organelles that undergo extensive remodeling during adipocyte differentiation, yet how their mechanical properties evolve during late-stage maturation remains unexplored. Here, we apply Brillouin microscopy to map the viscoelastic properties of LDs in differentiating white (WAT) and brown (BAT) adipocytes over 34 days. LDs exhibit lineage-associated mechanical maturation characterized by distinct terminal states, elastic-dissipative relationships, and geometry-mechanics coupling. WAT droplets reach a higher mechanical end point, whereas BAT droplets remain in a lower viscoelastic regime and exhibit distinct temporal evolution of dissipative behavior. Notably, WAT transitions to a size-independent mechanical state, indicating decoupling of stiffness from geometric growth and a shift toward internal organization-dominated mechanics, while BAT maintains geometry-mechanics coupling. Across both lineages, Brillouin shift and line width remain strongly correlated. These findings establish LDs as dynamically evolving mechanical entities and uncover organelle-scale mechanics as a previously unrecognized dimension of adipocyte late-stage differentiation.