Gain-of-function R225Q mutation in AMP-activated protein kinase gamma3 subunit increases mitochondrial biogenesis in glycolytic skeletal muscle

AMP-activated protein kinase (AMPK) is a heterotrimeric complex, composed of a catalytic subunit (alpha) and two regulatory subunits (beta and gamma), that works as a cellular energy sensor. The existence of multiple heterotrimeric complexes provides a molecular basis for the multiple roles of this highly conserved signaling system. The AMPK gamma3 subunit is predominantly expressed in skeletal muscle, mostly in type II glycolytic fiber types. We determined whether the AMPK gamma3 subunit has a role in signaling pathways that mediate mitochondrial biogenesis in skeletal muscle. We provide evidence that overexpression or ablation of the AMPK gamma3 subunit does not appear to play a critical role in defining mitochondrial content in resting skeletal muscle. However, overexpression of a mutant form (R225Q) of the AMPK gamma3 subunit (Tg-AMPKgamma3(225Q)) increases mitochondrial biogenesis in glycolytic skeletal muscle. These adaptations are associated with an increase in expression of the co-activator PGC-1alpha and several transcription factors that regulate mitochondrial biogenesis, including NRF-1, NRF-2, and TFAM. Succinate dehydrogenase staining, a marker of the oxidative profile of individual fibers, was also increased in transversal skeletal muscle sections of white gastrocnemius muscle from Tg-AMPKgamma3(225Q) mice, independent of changes in fiber type composition. In conclusion, a single nucleotide mutation (R225Q) in the AMPK gamma3 subunit is associated with mitochondrial biogenesis in glycolytic skeletal muscle, concomitant with increased expression of the co-activator PGC-1alpha and several transcription factors that regulate mitochondrial proteins, without altering fiber type composition

Trauma care does not discriminate: The association of race and health insurance with mortality following traumatic injury

BACKGROUND: Previous studies have reported that black race and lack of health insurance coverage are associated with increased mortality following traumatic injury. However, the association of race and insurance status with trauma outcomes has not been examined using contemporary, national, population-based data. METHODS: We used data from the National Inpatient Sample on 215,615 patients admitted to 1 of 836 hospitals following traumatic injury in 2010. We examined the effects of race and insurance coverage on mortality using two logistic regression models, one for patients younger than 65 years and the other for older patients. RESULTS: Unadjusted mortality was low for white (2.71%), black (2.54%), and Hispanic (2.03%) patients. We found no difference in adjusted survival for nonelderly black patients compared with white patients (adjusted odds ratio [AOR], 1.04; 95% confidence interval [CI], 0.90-1.19; p = 0.550). Elderly black patients had a 25% lower odds of mortality compared with elderly white patients (AOR, 0.75; 95% CI, 0.63-0.90; p = 0.002). After accounting for survivor bias, insurance coverage was not associated with improved survival in younger patients (AOR, 0.91; 95% CI, 0.77-1.07; p = 0.233). CONCLUSION: Black race is not associated with higher mortality following injury. Health insurance coverage is associated with lower mortality, but this may be the result of hospitals\u27 inability to quickly obtain insurance coverage for uninsured patients who die early in their hospital stay. Increasing insurance coverage may not improve survival for patients hospitalized following injury. LEVEL OF EVIDENCE: Epidemiologic and prognostic study, level III

Non-CpG methylation of the PGC-1alpha promoter through DNMT3B controls mitochondrial density

SummaryEpigenetic modification through DNA methylation is implicated in metabolic disease. Using whole-genome promoter methylation analysis of skeletal muscle from normal glucose-tolerant and type 2 diabetic subjects, we identified cytosine hypermethylation of peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1 α (PGC-1α) in diabetic subjects. Methylation levels were negatively correlated with PGC-1α mRNA and mitochondrial DNA (mtDNA). Bisulfite sequencing revealed that the highest proportion of cytosine methylation within PGC-1α was found within non-CpG nucleotides. Non-CpG methylation was acutely increased in human myotubes by exposure to tumor necrosis factor-α (TNF-α) or free fatty acids, but not insulin or glucose. Selective silencing of the DNA methyltransferase 3B (DNMT3B), but not DNMT1 or DNMT3A, prevented palmitate-induced non-CpG methylation of PGC-1α and decreased mtDNA and PGC-1α mRNA. We provide evidence for PGC-1α hypermethylation, concomitant with reduced mitochondrial content in type 2 diabetic patients, and link DNMT3B to the acute fatty-acid-induced non-CpG methylation of PGC-1α promoter