Tribbles 3 Overexpression Disrupts Exercise-Driven Glucose Metabolism and Mitochondrial Adaptations in Skeletal Muscle

Tribbles 3 (TRB3) functions as a pseudokinase that regulates metabolic and differentiation processes by inhibiting Akt activation via phosphorylation, but its specific role in exercise-induced skeletal muscle adaptation remains unclear. This study aims to determine the role of TRB3 in skeletal muscle adaptation in response to endurance exercise training using muscle-specific TRB3 transgenic (TG) and wild-type (WT) littermates. We hypothesized that increased TRB3 in muscle would reduce exercise-induced improvements in glucose metabolism and mitochondrial biogenesis. To test this, TG mice and WT littermates completed six weeks of either voluntary wheel running or controlled treadmill training, followed by assessments of glucose tolerance, gene expression, protein levels, and mitochondrial activity. TRB3 overexpression markedly reduced voluntary running distance than WT littermates indicating reduced exercise capacity (WT: 19.5 ± 2.2 km/week; TG: 11.7 ± 1.2 km/week). To control for differences in training intensity, we implemented an involuntary treadmill protocol that ensured equal workloads across genotypes. Under these standardized training conditions, TG mice displayed impaired glucose tolerance under both sedentary and trained conditions relative to WT mice. Furthermore, TG mice showed strong suppression of mRNA expression for glucose transporter 4 (GLUT4), hexokinase II (HXKII), and several mitochondrial biogenesis genes such as PGC1a, COX4, and citrate synthase. Although some mitochondrial and metabolic proteins were modestly elevated by training, these adaptations were blunted in TG muscles. Overall, these results show that skeletal muscle TRB3 disrupts exercise-induced metabolic adaptation by suppressing key transcriptional programs governing glucose uptake and mitochondrial biogenesis, identifying TRB3 as a negative regulator of exercise responsiveness in skeletal muscle. Funding was provided by National Institutes of Health grants R16GM149457, P50CA236733, and U54CA163069 to H.J.K. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.