Brock University, Department of Kinesiology, Centre for Muscle Metabolism and Biophysics, Faculty of Applied Health Sciences, St. Catharines, Ontario, Canada.
Am J Physiol Regul Integr Comp Physiol. 2012 Jan 1;302(1):R29-36. doi: 10.1152/ajpregu.00163.2011. Epub 2011 Oct 19.
Skeletal muscle lipid droplet-associated proteins (PLINs) are thought to regulate lipolysis through protein-protein interactions on the lipid droplet surface. In adipocytes, PLIN2 [adipocyte differentiation-related protein (ADRP)] is found only on lipid droplets, while PLIN5 (OXPAT, expressed only in oxidative tissues) is found both on and off the lipid droplet and may be recruited to lipid droplet membranes when needed. Our purpose was to determine whether PLIN5 is recruited to lipid droplets with contraction and to investigate the myocellular location and colocalization of lipid droplets, PLIN2, and PLIN5. Rat solei were isolated, and following a 30-min equilibration period, they were assigned to one of two groups: 1) 30 min of resting incubation and 2) 30 min of stimulation (n = 10 each). Immunofluorescence microscopy was used to determine subcellular content, distribution, and colocalization of lipid droplets, PLIN2, and PLIN5. There was a main effect for lower lipid and PLIN2 content in stimulated compared with rested muscles (P < 0.05). Lipid droplet distribution declined exponentially from the sarcolemma to the fiber center in the rested muscles (P = 0.001, r(2) = 0.99) and linearly in stimulated muscles (slope = -0.0023 ± 0.0006, P < 0.001, r(2) = 0.93). PLIN2 distribution declined exponentially from the sarcolemma to the fiber center in both rested and stimulated muscles (P < 0.0001, r(2) = 0.99 rest; P = 0.0004, r(2) = 0.98 stimulated), while PLIN5 distribution declined linearly (slope = -0.0085 ± 0.0009, P < 0.0001, r(2) = 0.94 rest; slope=-0.0078 ± 0.0010, P = 0.0003, r(2) = 0.91 stimulated). PLIN5-lipid droplets colocalized at rest with no difference poststimulation (P = 0.47; rest r(2) = 0.55 ± 0.02, stimulated r(2) = 0.58 ± 0.03). PLIN2-lipid droplets colocalized at rest with no difference poststimulation (P = 0.48; rest r(2) = 0.66 ± 0.02, stimulated r(2) = 0.65 ± 0.02). Contrary to our hypothesis, these results show that PLIN5 is not recruited to lipid droplets with contraction in isolated skeletal muscle.
骨骼肌脂滴相关蛋白（PLINs）被认为通过脂滴表面的蛋白质-蛋白质相互作用来调节脂解。在脂肪细胞中，PLIN2（脂肪分化相关蛋白（ADRP））仅存在于脂滴上，而 PLIN5（OXPAT，仅在氧化组织中表达）既存在于脂滴上也存在于脂滴外，并且在需要时可能被招募到脂滴膜上。我们的目的是确定 PLIN5 是否在收缩时被招募到脂滴上，并研究肌细胞内脂滴、PLIN2 和 PLIN5 的位置和共定位。分离大鼠比目鱼肌，在 30 分钟的平衡期后，将其分为两组之一：1）休息孵育 30 分钟和 2）刺激 30 分钟（每组 10 个）。免疫荧光显微镜用于确定脂滴、PLIN2 和 PLIN5 的亚细胞含量、分布和共定位。与休息肌肉相比，刺激肌肉中的脂滴和 PLIN2 含量较低，存在主要影响（P < 0.05）。在休息肌肉中，脂滴的分布从肌膜呈指数下降到纤维中心（P = 0.001，r² = 0.99），而在刺激肌肉中呈线性下降（斜率=-0.0023 ± 0.0006，P < 0.001，r² = 0.93）。在休息和刺激的肌肉中，PLIN2 的分布均从肌膜呈指数下降到纤维中心（P < 0.0001，r² = 0.99 休息；P = 0.0004，r² = 0.98 刺激），而 PLIN5 的分布呈线性下降（斜率=-0.0085 ± 0.0009，P < 0.0001，r² = 0.94 休息；斜率=-0.0078 ± 0.0010，P = 0.0003，r² = 0.91 刺激）。PLIN5-脂滴在休息时共定位，刺激后无差异（P = 0.47；休息 r² = 0.55 ± 0.02，刺激 r² = 0.58 ± 0.03）。PLIN2-脂滴在休息时共定位，刺激后无差异（P = 0.48；休息 r² = 0.66 ± 0.02，刺激 r² = 0.65 ± 0.02）。与我们的假设相反，这些结果表明，在分离的骨骼肌中，PLIN5 不会在收缩时被招募到脂滴上。
