Downregulation of the mitochondrial tRNA-derived fragment mt-tRF-LeuTAA enhances skeletal muscle insulin sensitivity

The mitochondrial tRNA-derived fragment mt-tRF-Leu TAA couples mitochondrial metabolism to insulin secretion. While its role in pancreatic β-cell function is well established, its broader impact on multi-organ glucose homeostasis remains unclear. In insulin target tissues, the presence, regulation, and mechanism of action of mt-tRF-Leu TAA are entirely unexplored. This study addresses this gap by investigating the impact of diet, nutritional status and diabetes on mt-tRF-Leu TAA regulation and by assessing its role in insulin sensitivity. We examined mt-tRF-Leu TAA levels in different insulin target tissues, including skeletal muscle, liver, and epididymal white adipose tissue, of rodents under physiological and pathological conditions. In skeletal muscle myotubes, we combined subcellular fractionation, antisense oligonucleotide-mediated knockdown and glucose uptake assays to determine mt-tRF-Leu TAA ’s mitochondrial localization and its influence on insulin sensitivity. mt-tRF-Leu TAA levels in mouse skeletal muscle decreased twofold in response to fasting. In myotubes, this tRNA fragment was enriched in mitochondria, and its downregulation enhanced glucose uptake. While the levels of mt-tRF-Leu TAA remained unchanged in insulin target tissues of diabetic mice, we observed a skeletal muscle-specific downregulation of mt-tRF-Leu TAA in young adult rats exhibiting insulin hypersensitivity. This study identifies mt-tRF-Leu TAA as a candidate regulator of skeletal muscle insulin response. By modulating both insulin secretion and action, mt-tRF-Leu TAA appears to play a notable role in systemic metabolic control, and may represent a promising target for diabetes treatment.