The Low Protein Diet induced Fetal Programming Leads to Mitochondrial Dysfunction and Metabolic Inflexibility in the Skeletal Muscle of Male Rats

A prenatal low-protein (LP) diet disrupts glucose homeostasis in adult offspring. Skeletal muscles are one of the main sites of glucose clearance, and mitochondria residing in the muscle fibers are central to glucose homeostasis. Our previous studies indicated that impaired mitochondrial health is central to dysregulated glucose metabolism in the gastrocnemius muscle of the LP programmed female rats. In addition, dysfunctional mitochondria are often an indicator of underlying irregularities in energy metabolism and metabolic inflexibility. Therefore, this study examined the mitochondrial function and metabolic flexibility in the skeletal muscles of prenatal LP programmed adult male rats. Pregnant Wistar rats were randomly allotted to a control diet (20% protein) or an isocaloric LP diet (6% protein). Standard laboratory rat chow was given to the dams and the pups, after delivery and weaning. All the experiments in the study were done with the skeletal muscles of 4-month-old male offspring. Gene, and protein expressions, mtDNA copy number, and electron microscopy were assessed in gastrocnemius (GS) muscle, and the mitochondrial oxygen consumption rate was determined using isolated Flexor digitorum brevis muscle fibers. The genes associated with mitochondrial outer membrane fusion, (Mfn1 and Mfn2), fission (Fis1), and biogenesis (Pgc1B, Nrf1, and Essra) were lower in the LP group. Further, our functional studies showed that the ATP-linked oxygen consumption rate (OCR), maximal, spare respiratory, and non-mitochondrial respiration-associated OCRs were lower in the LP rats. Interestingly, the mtDNA copy number was increased in the LP group. Further, the mRNA and protein expressions of Ndufb8, a key factor involved in the complex-I catalytic activity were downregulated in the LP group. In addition, the expression of genes linked to mitochondrial pyruvate transport (Mpc1) and metabolism (Pdha1) was lower in the LP group. In contrast, the expression of mitochondrial fatty acid transporters (Cpt1a and Cpt2) was higher in the LP when compared to the control group. However, electron microscopic analysis exhibited no difference in the mitochondrial ultrastructure in the LP muscle compared to the control. Altogether, our results indicate that the LP diet affects the mitochondrial complex-I integrity and dynamics and leads to altered substrate oxidation and mitochondrial dysfunction in the skeletal muscle of the male LP offspring.