Vitamin B3 rescues mitochondrial homeostasis in dexamethasone-induced skeletal muscle atrophy by reducing oxidative stress.

Abstract

Prolonged glucocorticoid exposure leads to oxidative stress, mitochondrial damage and impaired myogenesis reducing the overall health of the skeletal muscles. Dexamethasone (dex), a synthetic glucocorticoid, induces proteolysis and inflammation by disrupting cellular energetics and mitochondrial function. Vitamin B3 (vit B3), an NAD⁺ precursor, is known to be a natural antioxidant and anti-inflammatory compound. This study investigates the protective role of vit B3 against dex-induced skeletal muscle damage, focusing on mitochondrial homeostasis and the IKK/FoxO3a signalling axis. C2C12 myoblasts were treated with dex (200 µM) and/or vit B3 (1 mM). Oxidative stress, mitochondrial potential and DNA damage was evaluated using DCFDA, JC1, and γH2AX immunostaining, respectively. Gene expression analysis was performed to assess the mitochondrial fission/fusion and the extent of electron transport chain (ETC) gene expression. Protein expression of inflammatory (IKKα/β, NFκB) and atrophy markers were analysed using immunoblotting and flow cytometry. The extent of myogenic differentiation was evaluated using MyoD and MyHC1 immunostaining along with measurement of the morphometric parameters. Vit B3 treatment significantly enhanced C2C12 viability and reduced dex-induced ROS production while restoring Nrf2 expression. It prevented DNA damage and preserved mitochondrial membrane potential. The results also implicated increased mitochondrial fusion upon vit B3 treatment as seen by the elevated gene expression of Mfn1, Mfn2 and Opa1 and decreased fission as observed by the reduced expression of Fis1 and Drp1. The NADH levels were also seen to be rescued by vit B3 supplementation which translates to better energy production by the electron transport system. Additionally, vit B3 was observed to suppress inflammation and prevent muscle proteolysis by modulating an IKK/FoxO3a axis. Finally, vit B3 was able to improve differentiation as seen by the levels of MyoD and MyHC1 expression in the cells. Vit B3 acts in a multifaceted manner and reduces dex-induced skeletal muscle atrophy which is primarily a result of reduced oxidative stress and restored mitochondrial homeostasis. These findings highlight vit B3 as a potential therapeutic and nutritional supplement for maintaining the skeletal muscle health under myopathic conditions.