New insights into the function of lipid droplet-related proteins and lipid metabolism of salt-stimulated porcine biceps femoris: Label-free quantitative phosphoproteomics, morphometry and bioinformatics.

Abstract

Lipid droplets (LD) are important multifunctional organelles responsible for lipid metabolism of postmortem muscle. However, the dynamics in their building blocks (cores and layers) and phosphorylation of lipid droplet-related proteins (LDRP) regulating meat lipolysis remain unknown at salt-stimulated conditions. LDRP extracted from cured porcine biceps femoris (1% and 3% salt) were subjected to label-free quantitative phosphoproteomic analysis and LD morphological validation. Results indicated that 3% salt curing significantly decreased triglyceride (TG) content with increase in glycerol and decrease in LD fluorescence compared to 1% salt curing. Comparative phosphoproteomics showed that there were significant changes in phosphorylation at 386 sites on 174 LDRP between assayed groups (p < 0.05). These differential proteins were mainly involved in lipid and carbohydrate metabolism. Curing of 3% salt induced more site-specific phosphorylation of perilipin 1 (PLIN1, at Ser81) and adipose triglyceride lipase (ATGL, at Ser399) than 1%, whereas the phosphorylation (at Ser600) of hormone-sensitive lipase (HSL) was up-regulated. Ultrastructure imaging showed that LD were mostly associated with mitochondria, and the average diameter of LD decreased from 2.34 μm (1% salt) to 1.73 μm (3% salt). Phosphoproteomics unraveled salt-stimulated LDRP phosphorylation of cured porcine meat provoked intensified lipolysis. Curing of 3% salt allowed an enhanced lipolysis than 1% by up-regulating the phosphorylation sites of LDRP and recruited lipases. The visible splitting of LD, together with sarcoplasmic disorganization, supporting the lipolysis robustness following 3% salt curing. The finding provides optimization ideas for high-quality production of cured meat products. This article is protected by copyright. All rights reserved.