Figure 1.
Eight weeks of a high fat diet (HFD) elicits pre-diabetes.
(A) Fasted body mass was assessed before experimental diet began and after 4 and 8 weeks (N = 19 CON, 20 HFD). (B) Epididymal fat mass after 8 weeks of diet intervention (N = 19 CON, N = 20 HFD). (C) Intraperitoneal glucose tolerance test (IPGTT) performed after an overnight fast (16 hrs) 1 week before harvest (N = 19 CON, N = 18 HFD). (D) Plasma insulin levels assessed 4 weeks into diet intervention (8 hr fast, N = 10) and at IPGTT 45 minute time-point (16 hr fast, N = 4). Significance is represented by * vs. CON at same time point (A–D), a or b vs. 0 weeks within diet group, and c vs. 4 weeks within diet group, p<0.005.
Figure 2.
Morphometric changes are muscle-specific.
Serial cross-sections from control (CON, white bars in all graphs) and high fat diet (HFD, black bars in all graphs) fed mouse muscles [TA (top left only), gastrocnemius/plantaris complex (GP, all middle graphs), and soleus (all right graphs)] were examined for (A) fiber type composition, (B) area, (C) SDH stain intensity, and (D) IMCL stain intensity. Representative images of all stains used, performed on GP muscle cross-sections are shown to the left of graphs B–D with fiber type (type I, and types II- A, D, B) labeled with CON on the left and HFD on the right. (B) Metachromatic fiber type stain was used to assess fiber type. (C) SDH and (D) Oil-Red-O stains are graphically represented by arbitrary units (A.U.) of optical intensity measurements, with greater values for more intense stains and normalized to a percentage of all the control value means for each graph (% CON). All measurements were taken on an average of 51–331 total fibers/animal with a Nikon Eclipse 90i microscope (N = 3–4). Significance is represented by * vs. CON, p<0.005.
Figure 3.
Impaired palmitate and glucose oxidation in HFD single fibers.
(A) Palmitate (N = 19, average of 17 fibers/dish) and (B) glucose (N = 12 CON, N = 10 HFD, average of 23 fibers/dish) oxidation in single fibers derived from EDL and peroneus muscles was similarly impaired in mice fed a high-fat diet (HFD) compared to control (CON). Values were normalized to control values for each experiment and significance is represented by * vs. CON, p<0.005.
Figure 4.
Impaired oxidation, glycogen synthesis, and insulin stimulated response in HFD muscle.
Palmitate oxidation in whole (A) EDL (N = 4) and (B) soleus (N = 4) muscles is impaired with HFD. Both glucose oxidation in whole (C) EDL and (D) soleus and glycogen synthesis in whole (E) EDL and (F) soleus muscles with HFD demonstrate a significant blunted response to insulin pre-incubation (INSULIN), vs. no insulin pre-incubation (BASAL), in HFD muscle (N = 4–6, two-way ANOVA with Bonferonni post-tests between insulin conditions within diet). Significance is represented by * vs. CON (A–B), and vs. INSULN (C–F), p<0.005.
Figure 5.
Oxidative enzyme alterations are muscle specific.
Citrate synthase (CS) activity is unaltered in both (A) TA and (C) soleus muscle between control (CON) and high fat diet (HFD). Short chain 3-β-hydroxyacyl coenzyme-A dehydrogenase (SCHAD) activity is unaltered in (B) TA muscle, though (D) soleus muscle from HFD mice exhibits SCHAD activity 136% of CON. Significance is represented by * vs. CON, p<0.005.
Figure 6.
In situ contractile analysis reveals trend towards force decrements, yet unaltered peak force and fatigue.
Relative tetanic force production [in Newtons (N) per gram (g) of wet muscle mass] in the gastrocnemius/plantaris muscle group of high-fat diet (HFD) mice compared to control (CON) was (A) not different before (Pre) or after (Post) the fatigue protocol. (B) There was no difference between diets over all frequencies used to test force production pre-fatigue, however there was a significant main effect of diet post-fatigue. (C) Contractile force, relative to initial (% initial), throughout a 2 minute low-frequency fatigue protocol was not different between diet groups. Significance is represented by * vs. CON, p<0.005.