Role of adipose and hepatic atypical protein kinase C lambda (PKCλ) in the development of obesity and glucose intolerance

Abstract

PKCλ, an atypical member of the multifunctional protein kinase C family, has been implicated in the regulation of insulin-stimulated glucose transport and of the intracellular immune response. To further elucidate the role of this cellular regulator in diet-induced obesity and insulin resistance, we generated both liver (PKC-Alb) and adipose tissue (PKC-Ap2) specific knockout mice. Body weight, fat mass, food intake, glucose homeostasis and energy expenditure were evaluated in mice maintained on either chow or high fat diet (HFD). Ablation of PKCλ from the adipose tissue resulted in mice that were indistinguishable from their wild-type littermates. However, PKC-Alb mice were resistant to diet-induced obesity (DIO). Surprisingly this DIO resistance was not associated with either a reduction in caloric intake or an increase in energy expenditure as compared with their wild-type littermates. Furthermore, these mice displayed an improvement in glucose tolerance. When maintained on chow diet, these mice were similar to wild types in respect to body weight and fat mass, yet insulin sensitivity was impaired compared with wt littermates. Taken together these data suggest that hepatic PKCλ is modulating insulin-mediated glucose turnover and response to high fat diet feeding, thus offering a deeper understanding of an important target for anti-obesity therapeutics.

Keywords: atypical protein kinase C-lambda; diet induced obesity; energy expenditure; glucose tolerance; insulin resistance.

Figure 1. Body weight (A and B), fat mass (C and D) and lean mass (E and F) growth curves of chow- or HFD-fed PKCλ^fl/fl Cre^Alb (closed circles) and PKCλ^wt/wt mice (open circles). Cumulative food intake was monitored throughout the study (G and H). All data are represented as mean ± SEM in 6–7 age-matched, male mice. *p < 0.05, **p < 0.01, ***p < 0.001, as determined by 2-way ANOVA.

Figure 2. Body weight of 40-week-old, chow- (A) or HFD-fed (B) PKCλ^fl/fl Cre^Alb (closed bars) and PKCλ^wt/wt mice (open bars). All data are represented as mean ± SEM in 6–7 age-matched, male mice. *p < 0.05 as determined by Student’s t-test.

Figure 3. Dynamic and average energy expenditure (A and B), respiratory quotient (C and D) and locomotor activity (E and F) in chow-fed PKCλ^fl/fl Cre^Alb (closed circles/bars) and PKCλ^wt/wt (open circles/bars) mice as measured by indirect calorimetry. All data are represented as mean ± SEM in 6–7 age-matched, male mice. No differences were determined by 2-way ANOVA.

Figure 4. Dynamic and average energy expenditure (A and B), respiratory quotient (C and D) and locomotor activity (E and F) in HFD-fed PKCλ^fl/fl Cre^Alb (closed circles/bars) and PKCλ^wt/wt (open circles/bars) mice as measured by indirect calorimetry. All data are represented as mean ± SEM in 6–7 age-matched, male mice. No differences were determined by 2-way ANOVA.

Figure 5. Blood glucose levels (A and B) of chow- and HFD-fed PKCλ^fl/fl Cre^Alb (closed bars) and PKCλ^wt/wt (open bars) mice following 6 h fast. Plasma insulin (C and D) in HFD-fed PKCλ^fl/fl Cre^Alb (closed bars) and PKCλ^wt/wt (open bars) mice following 6 h fast. HOMA-INDEX (e and f) in HFD-fed PKCλ^fl/fl Cre^Alb (closed bars) and PKCλ^wt/wt (open bars) mice. All data are represented as mean ± SEM in 6–7 age-matched, male mice at week 25. *p < 0.05 as determined by one-way ANOVA.

Figure 6. Glucose tolerance as assessed by glucose excursion (A and B) and area under the curve analyses (inset of A and B) of chow- and HFD-fed PKCλ^fl/fl Cre^Alb (closed circles) and PKCλ^wt/wt (open circles) mice following a 2 g/kg dose of ip glucose at week 20. Insulin tolerance as assessed by glucose excursion (C and D) and glucose clearance [as % of initial blood glucose (E and F)] of chow- and HFD-fed PKCλ^fl/fl Cre^Alb (closed circles) and PKCλ^wt/wt (open circles) mice following a 0.75 U/kg dose of ip insulin at week 25. All studies were conducted after a 6 h fast and all data are represented as mean ± SEM in 6–7 age-matched, male mice. *p < 0.05 as determined by 2-way ANOVA or Student’s t-test.

Figure 7. Pyruvate tolerance as assessed by glucose excursion (A and B) and glucose appearance during the first 30 min following ip pyruvate challenge (2 g/kg) (C and D) of chow- and HFD-fed PKCλ^fl/fl Cre^Alb (closed circles) and PKCλ^wt/wt (open circles) mice following a 2 g/kg dose of ip pyruvate at week 26. All data are represented as mean ± SEM in 6–7 age-matched, male mice. *p < 0.05 as determined by Student’s t-test.

Figure 8. Fasting cholesterol (A), triglyceride (B) and alanine transaminase concentrations of chow- and HFD-fed PKCλ^fl/fl Cre^Alb (closed bars) and PKCλ^wt/wt (open bars) mice at sacrifice. All data are represented as mean ± SEM in 6–7 age-matched, male mice. **p < 0.01 as determined by 1-way ANOVA.

Figure 9. Body weight (A), fat mass (B), lean mass (C) and cumulative food intake (D) in PKCλ^fl/fl Cre^aP2 (closed circles) and PKCλ^wt/wt mice (open circles). Glucose tolerance as assessed by glucose excursion (E) and area under the curve analyses (inset of E) of 20-week-old, chow-fed PKCλ^fl/fl Cre^Alb (closed circles) and PKCλ^wt/wt (open circles) mice following a 2 g/kg dose of ip glucose at week 20. All data are represented as mean ± SEM in 6–7 age-matched, male mice. No differences were determined by 2-way ANOVA or Student’s t-test.

Figure 10. Dynamic and average energy expenditure (A and B), respiratory quotient (C and D) and locomotor activitiy (E and F) in 20-week-old, chow-fed PKCλ^fl/fl Cre^aP2 (closed circles) and PKCλ^wt/wt (open circles) mice as measured by indirect calorimetery. All data are represented as mean ± SEM in 6–7 age-matched, male mice. No differences were determined by 2-way ANOVA.