Abstract
Mitochondrial dysfunction is a major contributor to skin aging. Glutamic acid (Glu) acts as an anaplerotic substrate for the tricarboxylic acid cycle to support ATP production, but senescent fibroblasts take up Glu poorly due to down-regulation of membrane amino-acid transporters. This study investigated whether HA-Glu, a covalent conjugate of hyaluronic acid and glutamic acid, could improve mitochondrial function in senescent fibroblasts by facilitating intracellular glutamate delivery through an alternative uptake pathway, potentially reducing reliance on SLC1A3-mediated transport. Time-course confocal microscopy revealed progressive intracellular accumulation of FITC-tagged HA-Glu in human dermal fibroblasts, and blocking CD44 largely prevented this cellular uptake. In UVA-exposed fibroblasts, HA-Glu restored mitochondrial membrane potential, lowered mitochondrial superoxide production, and raised cellular glutathione and ATP content. These effects were stronger than those produced by equivalent doses of free Glu or glutamine. HA-Glu also reversed stress-triggered mitochondrial swelling. Pharmacological inhibition of SLC1A3 using UCPH-101 completely abrogated the anti-senescence activity of free Glu, while HA-Glu retained its protective effects and sustained the expression of type I and III collagens, elastin and fibronectin. In UVB-treated male SKH-1 hairless mice (n = 3 per group), topical HA-Glu smoothed rough skin, restored dermal collagen deposition and diminished IL-6 and MMP-1 signals. Collectively, these findings support a model in which HA-Glu improves mitochondrial function in senescent fibroblasts, potentially through CD44-associated intracellular glutamate (Glu) delivery, and may attenuate UV-induced skin photoaging.