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Obesity-induced insulin resistance in human skeletal muscle is characterised by defective activation of p42/p44 MAP kinase.

Ruiz-Alcaraz AJ, Lipina C, Petrie JR, Murphy MJ, Morris AD, Sutherland C, Cuthbertson DJ - PLoS ONE (2013)

Bottom Line: The most striking abnormality was significantly reduced insulin-induced activation of p42/44 MAP kinase, measured by specific assay, in the volunteers with poor insulin sensitivity.However, there was no relationship between individuals' BMI or M-value and protein expression/phosphorylation of IRS1, PKB, or p42/44 MAP kinase protein, under basal or hyperinsulinaemic conditions.In the few individuals with poor insulin sensitivity but preserved p42/44 MAP kinase activation, other signalling defects were evident.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology B and Immunology, School of Medicine, University of Murcia, Murcia, Spain.

ABSTRACT
Insulin resistance (IR), an impaired cellular, tissue and whole body response to insulin, is a major pathophysiological defect of type 2 diabetes mellitus. Although IR is closely associated with obesity, the identity of the molecular defect(s) underlying obesity-induced IR in skeletal muscle remains controversial; reduced post-receptor signalling of the insulin receptor substrate 1 (IRS1) adaptor protein and downstream effectors such as protein kinase B (PKB) have previously been implicated. We examined expression and/or activation of a number of components of the insulin-signalling cascade in skeletal muscle of 22 healthy young men (with body mass index (BMI) range, 20-37 kg/m(2)). Whole body insulin sensitivity (M value) and body composition was determined by the hyperinsulinaemic (40 mU. min(-1).m(-2).), euglycaemic clamp and by dual energy X-ray absorptiometry (DEXA) respectively. Skeletal muscle (vastus lateralis) biopsies were taken before and after one hour of hyperinsulinaemia and the muscle insulin signalling proteins examined by western blot and immunoprecipitation assay. There was a strong inverse relationship between M-value and BMI. The most striking abnormality was significantly reduced insulin-induced activation of p42/44 MAP kinase, measured by specific assay, in the volunteers with poor insulin sensitivity. However, there was no relationship between individuals' BMI or M-value and protein expression/phosphorylation of IRS1, PKB, or p42/44 MAP kinase protein, under basal or hyperinsulinaemic conditions. In the few individuals with poor insulin sensitivity but preserved p42/44 MAP kinase activation, other signalling defects were evident. These findings implicate defective p42/44 MAP kinase signalling as a potential contributor to obesity-related IR in a non-diabetic population, although clearly multiple signalling defects underlie obesity associated IR.

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Fold activation of ERK by insulin according to body mass index or M value.(A) Body mass index (r = 0.73; p = 0.0009) or (B) M value (r = 0.52; p = 0.04).
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pone-0056928-g005: Fold activation of ERK by insulin according to body mass index or M value.(A) Body mass index (r = 0.73; p = 0.0009) or (B) M value (r = 0.52; p = 0.04).

Mentions: It is widely appreciated that the western blot technique is semi-quantitative (albeit technically relatively straightforward). Therefore, since there was an indication that insulin regulation of p42/44 MAPK phosphorylation may be reduced in the more insulin resistant population, we decided to perform a more quantitative analysis of p42/44 MAPK activation. p42 MAPK and p44 MAPK were immunoprecipitated prior to an in vitro assay of activity, for the pre- and post-insulin biopsies, for 17 of the 22 volunteers, covering the full range of BMI and M-values. As with western blot we found that there was a great deal of inter-individual variability in the basal level of activity. There was no significant correlation between either basal activity or post-insulin p42/p44 MAPK activity levels, and M-value or BMI (Figure 5). However there was an inverse correlation between fold-induction of p42/44 MAPK activity by insulin and body mass index (r = 0.73; p = 0.0009) (Figure 5A) and a significant correlation between p42/44 MAPK activity in response to insulin and M value (r = 0.52; p = 0.04) (Figure 5B). Thus, whether measured against the degree of obesity or IR, the data indicates a close relationship between defective response to insulin of p42/44 MAPK activity in muscle and the clinical measures of pre-diabetes. This suggests that abnormal p42/p44 MAPK response to insulin in skeletal muscle is a better marker of whole body insulin resistance than the response of the PI3K-PKB pathway, at least in obese non-diabetic individuals.


Obesity-induced insulin resistance in human skeletal muscle is characterised by defective activation of p42/p44 MAP kinase.

Ruiz-Alcaraz AJ, Lipina C, Petrie JR, Murphy MJ, Morris AD, Sutherland C, Cuthbertson DJ - PLoS ONE (2013)

Fold activation of ERK by insulin according to body mass index or M value.(A) Body mass index (r = 0.73; p = 0.0009) or (B) M value (r = 0.52; p = 0.04).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585240&req=5

pone-0056928-g005: Fold activation of ERK by insulin according to body mass index or M value.(A) Body mass index (r = 0.73; p = 0.0009) or (B) M value (r = 0.52; p = 0.04).
Mentions: It is widely appreciated that the western blot technique is semi-quantitative (albeit technically relatively straightforward). Therefore, since there was an indication that insulin regulation of p42/44 MAPK phosphorylation may be reduced in the more insulin resistant population, we decided to perform a more quantitative analysis of p42/44 MAPK activation. p42 MAPK and p44 MAPK were immunoprecipitated prior to an in vitro assay of activity, for the pre- and post-insulin biopsies, for 17 of the 22 volunteers, covering the full range of BMI and M-values. As with western blot we found that there was a great deal of inter-individual variability in the basal level of activity. There was no significant correlation between either basal activity or post-insulin p42/p44 MAPK activity levels, and M-value or BMI (Figure 5). However there was an inverse correlation between fold-induction of p42/44 MAPK activity by insulin and body mass index (r = 0.73; p = 0.0009) (Figure 5A) and a significant correlation between p42/44 MAPK activity in response to insulin and M value (r = 0.52; p = 0.04) (Figure 5B). Thus, whether measured against the degree of obesity or IR, the data indicates a close relationship between defective response to insulin of p42/44 MAPK activity in muscle and the clinical measures of pre-diabetes. This suggests that abnormal p42/p44 MAPK response to insulin in skeletal muscle is a better marker of whole body insulin resistance than the response of the PI3K-PKB pathway, at least in obese non-diabetic individuals.

Bottom Line: The most striking abnormality was significantly reduced insulin-induced activation of p42/44 MAP kinase, measured by specific assay, in the volunteers with poor insulin sensitivity.However, there was no relationship between individuals' BMI or M-value and protein expression/phosphorylation of IRS1, PKB, or p42/44 MAP kinase protein, under basal or hyperinsulinaemic conditions.In the few individuals with poor insulin sensitivity but preserved p42/44 MAP kinase activation, other signalling defects were evident.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology B and Immunology, School of Medicine, University of Murcia, Murcia, Spain.

ABSTRACT
Insulin resistance (IR), an impaired cellular, tissue and whole body response to insulin, is a major pathophysiological defect of type 2 diabetes mellitus. Although IR is closely associated with obesity, the identity of the molecular defect(s) underlying obesity-induced IR in skeletal muscle remains controversial; reduced post-receptor signalling of the insulin receptor substrate 1 (IRS1) adaptor protein and downstream effectors such as protein kinase B (PKB) have previously been implicated. We examined expression and/or activation of a number of components of the insulin-signalling cascade in skeletal muscle of 22 healthy young men (with body mass index (BMI) range, 20-37 kg/m(2)). Whole body insulin sensitivity (M value) and body composition was determined by the hyperinsulinaemic (40 mU. min(-1).m(-2).), euglycaemic clamp and by dual energy X-ray absorptiometry (DEXA) respectively. Skeletal muscle (vastus lateralis) biopsies were taken before and after one hour of hyperinsulinaemia and the muscle insulin signalling proteins examined by western blot and immunoprecipitation assay. There was a strong inverse relationship between M-value and BMI. The most striking abnormality was significantly reduced insulin-induced activation of p42/44 MAP kinase, measured by specific assay, in the volunteers with poor insulin sensitivity. However, there was no relationship between individuals' BMI or M-value and protein expression/phosphorylation of IRS1, PKB, or p42/44 MAP kinase protein, under basal or hyperinsulinaemic conditions. In the few individuals with poor insulin sensitivity but preserved p42/44 MAP kinase activation, other signalling defects were evident. These findings implicate defective p42/44 MAP kinase signalling as a potential contributor to obesity-related IR in a non-diabetic population, although clearly multiple signalling defects underlie obesity associated IR.

Show MeSH
Related in: MedlinePlus