Effect of myostatin depletion on weight gain, hyperglycemia, and hepatic steatosis during five months of high-fat feeding in mice

Abstract

The marked hypermuscularity in mice with constitutive myostatin deficiency reduces fat accumulation and hyperglycemia induced by high-fat feeding, but it is unclear whether the smaller increase in muscle mass caused by postdevelopmental loss of myostatin activity has beneficial metabolic effects during high-fat feeding. We therefore examined how postdevelopmental myostatin knockout influenced effects of high-fat feeding. Male mice with ubiquitous expression of tamoxifen-inducible Cre recombinase were fed tamoxifen for 2 weeks at 4 months of age. This depleted myostatin in mice with floxed myostatin genes, but not in control mice with normal myostatin genes. Some mice were fed a high-fat diet (60% of energy) for 22 weeks, starting 2 weeks after cessation of tamoxifen feeding. Myostatin depletion increased skeletal muscle mass ∼30%. Hypermuscular mice had ∼50% less weight gain than control mice over the first 8 weeks of high-fat feeding. During the subsequent 3 months of high-fat feeding, additional weight gain was similar in control and myostatin-deficient mice. After 5 months of high-fat feeding, the mass of epididymal and retroperitoneal fat pads was similar in control and myostatin-deficient mice even though myostatin depletion reduced the weight gain attributable to the high-fat diet (mean weight with high-fat diet minus mean weight with low-fat diet: 19.9 g in control mice, 14.1 g in myostatin-deficient mice). Myostatin depletion did not alter fasting blood glucose levels after 3 or 5 months of high-fat feeding, but reduced glucose levels measured 90 min after intraperitoneal glucose injection. Myostatin depletion also attenuated hepatic steatosis and accumulation of fat in muscle tissue. We conclude that blocking myostatin signaling after maturity can attenuate some of the adverse effects of a high-fat diet.

Figure 1. Mean (±SEM) change in total body mass.

Top panel shows cumulative weight gains after changing dietary fat from 13% to 60% of energy, and lower panel shows biweekly weight changes independent of previous measures. IPGTT = intraperitoneal glucose tolerance test. *P<0.05 (adjusted for multiple comparisons) for difference between normal and myostatin-depleted.

Figure 2. Mean (+SEM) muscle and intra-abdominal adipose tissue mass.

Myostatin-deficient (gray bars) and control mice (white bars) were fed a normal low-fat diet (13% of energy from fat) or were fed a high-fat diet (60% of energy from fat) for the final 22 weeks of the experiment. Each bar represents the mean and SEM of 12–15 mice. *P<0.001 versus mice with normal myostatin levels.

Figure 3. Mean (+SEM) blood glucose concentrations.

Bars represent means, whiskers represent SEM. Number of values included in each mean are shown at the bottom of each bar. *P<0.01 vs. normal myostatin group represented by adjacent bar. #P<0.02 vs. low-fat group with same myostatin status.

Figure 4. Mean (+SEM) lipid mass in triceps brachii muscles.

Esterified + non-esterified fatty acid content (palmitic + palmitoleic + stearic + oleic + linoleic acids, which accounted for ∼90% of total fatty acid mass) was determined by gas chromatography. *P<0.001 vs. low-fat group with normal myostatin expression. #P<0.001 vs. high-fat group with normal myostatin expression and P<0.05 vs. myostatin-deficient low-fat group. Data from 6 mice per genotype/diet condition.

Figure 5. Hepatic steatosis scores and representative micrographs of liver sections.

Distribution of steatosis scores (A) is based on examination of 12 mice with normal myostatin expression and 13 myostatin-deficient mice, all of which received the high-fat diet. Mice fed a low-fat diet did not have hepatic fat accumulation (B, Osmium H&E×250). Mice with normal myostatin expression had significant hepatic steatosis after 5 months of high-fat feeding (C×250; D×500). Larger lipid droplets often lift off the tissue leaving the clear spaces seen in the micrographs. Less fat accumulation was evident in livers of myostatin-deficient mice fed a high-fat diet for 5 months (E×250; F×500).