👤 E W Needham

Calorie restriction (CR; calorie intake reduced by ∼20%-40% below ad libitum, AL, intake) potentiates skeletal muscle insulin sensitivity during old age by incompletely understood mechanisms. We aimed to identify CR-induced changes in muscle insulin signaling that may explain this enhanced sensitivity. We examined how CR (65% of AL intake for 8-weeks) alters muscle insulin action and signaling in aged rats (24-month old) of both sexes. We assessed insulin-stimulated glucose uptake (ISGU) in muscle together with deep phosphoproteomic profiling. CR enhanced ISGU in both sexes, with higher ISGU in females regardless of diet. We identified 590 diet-responsive phosphosites, indicating extensive CR-induced remodelling of muscle phosphorylation, particularly within structural and contractile pathways. Strikingly, 70% of these sites were sex-specific. Numerous insulin-responsive sites were identified (193 in females; 107 in males) with 60 overlapping sites. The magnitude of the insulin-effects among all significantly regulated sites correlated between sexes. S1443 phosphorylation on EH domain-binding protein 1-like protein-1 (Ehbp1l1; a potential regulator of Rab proteins that control GLUT4 glucose transporter trafficking) was insulin-responsive in both sexes but only associated to ISGU in females. Personalized phosphoproteomic analysis also identified insulin-responsive sites on Leiomodin-1 (Lmod1) that correlated with ISGU across individuals. Both Lmod1 and Ehbp1l1 have strong genetic association with glycemic traits in humans, reinforcing their translational relevance. This study revealed sex-dependent and sex-independent phosphosignaling mechanisms that associate with muscle insulin responsiveness as well as hundreds of sex-specific, CR-responsive phosphosites. These findings provide a rich resource for future research on CR and insulin sensitivity. Show less

We examined the impact of a G-->A mutation at position -75 of the apolipoprotein AI gene promoter in subjects with hypertriglyceridaemia from two racial groups, Caucasians (n = 52) and Japanese (n = 19) compared to their controls (n = 56 and n = 21 respectively). The mutation was genotyped by the polymerase chain reaction and subsequent digestion using HpaII, and BstNI. We found no significant differences in allele frequency in either control-control or case-control comparisons in European and Japanese populations. Linkage disequilibrium was observed between the mutation and the common alleles of two restriction fragment length polymorphisms, MspI and SstI located in the APOA1 and APOC3 genes, respectively, in the Japanese population. On the basis of these results, the G-75-->A mutation is unlikely to be aetiological in predisposing to hypertriglyceridaemia. Show less