Severe energy deficit upregulates leptin receptors, leptin signaling, and PTP1B in human skeletal muscle

Abstract

In obesity, leptin receptors (OBR) and leptin signaling in skeletal muscle are downregulated. To determine whether OBR and leptin signaling are upregulated with a severe energy deficit, 15 overweight men were assessed before the intervention (PRE), after 4 days of caloric restriction (3.2 kcal . kg body wt(-1).day(-1)) in combination with prolonged exercise (CRE; 8 h walking + 45 min single-arm cranking/day) to induce an energy deficit of similar to 5,500 kcal/day, and following 3 days of control diet (isoenergetic) and reduced exercise (CD). During cre, the diet consisted solely of whey protein (n = 8) or sucrose (n = 7; 0.8 g . kg body wt(-1).day(-1)). Muscle biopsies were obtained from the exercised and the nonexercised deltoid muscles and from the vastus lateralis. From PRE to CRE, serum glucose, insulin, and leptin were reduced. OBR expression was augmented in all examined muscles associated with increased maximal fat oxidation. Compared with PRE, after CD, phospho-Tyr(1141)OBR, phospho-Tyr(985)OBR, JAK2, and phosphoTyr(1007/1008)JAK2 protein expression were increased in all muscles, whereas STAT3 and phospho-Tyr(705)STAT3 were increased only in the arms. The expression of protein tyrosine phosphatase 1B (PTP1B) in skeletal muscle was increased by 18 and 45\% after CRE and CD, respectively (P < 0.05). Suppressor of cytokine signaling 3 (SOCS3) tended to increase in the legs and decrease in the arm muscles (ANOVA interaction: P < 0.05). Myosin heavy chain I isoform was associated with obr protein expression (r = -0.75), phospho-Tyr(985)OBR (r = 0.88), and phospho-tyr(705)stat3/stat3 (r = 0.74). In summary, despite increased PTP1B expression, skeletal muscle OBR and signaling are upregulated by a severe energy deficit with greater response in the arm than in the legs likely due to SOCS3 upregulation in the leg muscles.