Nicotinamide riboside targets mitochondrial unfolded protein response to reduce alcohol-induced damage in Kupffer cells

Abstract

The pathogenesis of alcohol-related liver disease (ALD) is closely linked to mitochondrial dysfunction and impaired cellular energy metabolism. In this study, we explored how ethanol triggers inflammation, oxidative stress, and mitochondrial dysfunction in Kupffer cells, i.e.hepatic resident macrophages, primarily focusing on the mitochondrial unfolded protein response (UPR^mt) using immortalized mouse Kupffer cells (ImKCs) and mouse primary KCs. The UPR^mt is a cellular defense mechanism activated in response to the perturbation of mitochondrial proteostasis to maintain mitochondrial integrity and function by upregulating the expression of mitochondrial chaperones and proteases. We also determined whether nicotinamide riboside (NR), a NAD⁺ precursor, could mitigate ethanol-triggered cellular damage. When ImKCs were exposed to 80 mm ethanol for 72 h, they displayed inflammation, oxidative stress, and impaired mitochondrial function with decreased mitochondrial content and deformed mitochondrial crista structure. NR, however, counteracted the effects of ethanol. Furthermore, ethanol increased mRNA and protein levels of UPR^mt genes, such as mitochondrial chaperones and proteases, which were attenuated by NR. Notably, the ethanol-induced shift in the entry of activating transcription factor 5 (ATF5), a putative transcriptional regulator of UPR^mt, to the nucleus from the mitochondria was abolished by NR. The induction of UPR^mt genes by ethanol was significantly repressed when Atf5 was knocked down, indicating the role of ATF5 in the induction of UPR^mt genes in ImKCs exposed to ethanol. We also confirmed the induction of UPR^mt gene expression in mouse and human livers exposed to alcohol. Our findings demonstrate the ability of NR to alleviate ethanol-induced oxidative stress, inflammation, and mitochondrial dysfunction, partly by modulating the ATF5-dependent UPR^mt pathway in ImKCs, suggesting its potential for ALD therapy. © 2024 The Pathological Society of Great Britain and Ireland.