Short and long-term effect of reproduction on mitochondrial dynamics and autophagy in rats

We evaluated mitochondrial dynamics and autophagy by investigating the acute and long-term changes in the liver and skeletal muscle of rats in multiple reproductive stages. A total of 48 rats were used. Rats were randomly assigned to three groups (n = 16 per group): nonreproductive females; females that became pregnant, gave birth, but had their pups removed at birth, and thus, did not lactate; and females that experienced pregnancy, gave birth, and were allowed to lactate. Each group was further divided into two-time subgroups (n = 8 per subgroup) and data were collected at a time-point corresponding to 1) peak lactation (day 14 of lactation) in the lactating animals (4 months of age) and 2) 15 weeks after parturition (12 weeks post-weaning in lactating animals; 7 months of age). Levels of several proteins involved in mitochondrial dynamics and the autophagy system were measured in the liver and skeletal muscle. Beclin1 protein levels in the liver were higher in non-lactating rats two weeks after parturition, while Beclin1 protein levels were highest in 7-month-old animals that had previously experienced a standard reproductive event that included pregnancy and a full 3 week of lactation. These animals also exhibited higher protein levels of the mitochondrial fusion marker Mfn2 in the liver. In skeletal muscle, we also observed increased protein levels of the mitochondrial fission marker DRP1 in non-lactating animals compared to animals that lactated. In summary, our data provide insightful information on the mechanisms that influence liver and skeletal muscle remodeling in response to the metabolic challenges of reproduction, and lactation in particular. Autophagy remodeling and mitochondrial fusion seem to coincide with liver mass size during the lactation stage of reproduction. Our findings highlight the complex changes that occur in the liver and skeletal muscle during reproduction, and highlights the remarkable plasticity required during this demanding metabolic feat.