Induced Cre‐mediated knockdown of Brca1 in skeletal muscle reduces mitochondrial respiration and prevents glucose intolerance in adult mice on a high‐fat diet

Abstract

The breast cancer type 1 susceptibility protein (Brca1) is a regulator of DNA repair in mammary gland cells; however, recent cell culture evidence suggests that Brca1 influences other processes, including those in nonmammary cells. In this study, we sought to determine whether Brca1 is necessary for metabolic regulation of skeletal muscle using a novel in vivo mouse model. We developed an inducible skeletal muscle-specific Brca1knockout (BRCA1KO) model to test whether Brca1 expression is necessary for maintenance of metabolic function of skeletal muscle when exposed to a high-fat diet (HFD). Our data demonstrated that deletion of Brca1 prevented HFD-induced alterations in glucose and insulin tolerance. Irrespective of diet, BRCA1KO mice exhibited significantly lower ADP-stimulated complex I mitochondrial respiration rates compared to age-matched wild-type (WT) mice. The data show that Brca1 has the ability to localize to the mitochondria in skeletal muscle and that BRCA1KO mice exhibit higher whole-body CO production, respiratory exchange ratio, and energy expenditure, compared with the WT mice. Our results demonstrate that loss of Brca1 in skeletal muscle leads to dysregulated metabolic function, characterized by decreased mitochondrial respiration. Thus, any condition that results in loss of Brca1 function could induce metabolic imbalance in skeletal muscle.-Jackson, K. C., Tarpey, M. D., Valencia, A. P., Iñigo, M. R., Pratt, S. J., Patteson, D. J., McClung, J. M., Lovering, R. M., Thomson, D. M., Spangenburg, E. E. Induced Cre-mediated knockdown of Brca1 in skeletal muscle reduces mitochondrial respiration and prevents glucose intolerance in adult mice on a high-fat diet.

Induced in vivo knockdown of the Brca1 gene in skeletal muscle results in skeletal muscle weakness

“…) and isolated mitochondria (Jackson et al . ) suggest that oxidative capacity might be uniquely affected in the Brca1KO smi mice; thus, we aimed to directly assess mitochondrial respiration. Accordingly, we employed a permeabilized muscle fibre bundle approach to assess mitochondrial respiration (because it maintains the mitochondria in their native state at the same time as still maintaining the natural architecture of the muscle cell).…”

“…We have previously demonstrated that this model results in the deletion of Brca1 protein content specifically in the skeletal muscle with no off‐target effects (Jackson et al . ). We confirmed the deletion of exon 11 in the current cohort of animals at 30–34 weeks of age via PCR‐amplified verification of DNA recombination (data not shown), as described previously (Jackson et al .…”

“…We confirmed the deletion of exon 11 in the current cohort of animals at 30–34 weeks of age via PCR‐amplified verification of DNA recombination (data not shown), as described previously (Jackson et al . ). Successful knockdown of Brca1 mRNA was also confirmed in the plantaris muscle for each group (data not shown).…”

“…To date, our laboratory has shown that BRCA1 and Brca1 are expressed in human and murine skeletal muscle, respectively, and also that Brca1 localizes within skeletal muscle to the nucleus and mitochondria (Jackson et al . , ). Furthermore, we have identified BRCA1/Brca1 as a regulator of skeletal muscle metabolism via BRCA1–p‐ACC interactions (Jackson et al .…”

“…) and shown that skeletal muscle‐specific loss of Brca1 protects mice against high‐fat diet‐induced perturbations in glucose and insulin tolerance (Jackson et al . ). The extent of BRCA1/Brca1 regulation on skeletal muscle function remains largely unknown.…”