Mitochondrial dysfunction is associated with a variety of human diseases including neurodegeneration, diabetes, nonalcohol fatty liver disease (NAFLD), and cancer, but its underlying causes are incompletely understood. Using the human hepatic cell line HepG2 as a model, we show here that endoplasmic reticulum-associated degradation (ERAD), an ER protein quality control process, is critically required for mitochondrial function in mammalian cells. Pharmacological inhibition or genetic ablation of key proteins involved in ERAD increased cell death under both basal conditions and in response to proinflammatory cytokines, a situation frequently found in NAFLD. Decreased viability of ERAD-deficient HepG2 cells was traced to impaired mitochondrial functions including reduced ATP production, enhanced reactive oxygen species (ROS) accumulation, and increased mitochondrial outer membrane permeability. Transcriptome profiling revealed widespread down-regulation of genes underpinning mitochondrial functions, and up-regulation of genes associated with tumor growth and aggression. These results highlight a critical role for ERAD in maintaining mitochondrial functional and structural integrity and raise the possibility of improving cellular and organismal mitochondrial function via enhancing cellular ERAD capacity.

Background: Dendritic cells (DCs) are versatile professional antigen-presenting cells and play an instrumental role in the generation of antigen-specific T-cell responses. Modulation of DC function holds promise as an effective strategy to improve anti-tumor immunotherapy efficacy and enhance self-antigen tolerance in autoimmune diseases.Methods: Wild-type (WT) and TLR2 knockout (KO) mice at 2 weeks of age were injected intraperitoneally (i.p.) with a single dose of diethylnitrosamine (DEN) to induce hepatocellular carcinoma (HCC). Four weeks later, WT and KO mice were randomly divided into control and treatment groups and treated once every two days for 30 weeks with phosphate buffered saline (PBS) and a mix of 4 TLR2-activating lactic acid-producing probiotics (LAP), respectively. Mice were euthanized after 30 weeks of LAP treatment and their liver tissues were collected for gene expression, histological, flow cytometric and single-cell RNA sequencing analyses.Results: We demonstrate here that oral administration of a mix of TLR2-activating LAP triggers a marked accumulation of regulatory DCs (rDCs) in the liver of mice. LAP-treated mice are protected from DEN-induced liver injury, fibrosis and HCC in a TLR2-dependent manner. Single-cell transcriptome profiling revealed that LAP treatment determines an immunosuppressive hepatic T-cell program that is characterized by a significantly reduced cytotoxic activity. The observed functional changes of T cells correlated well with the presence of a hepatic DC subset displaying a regulatory or tolerogenic transcriptional signature.Conclusion: Overall, these data suggest that stimulation of regulatory dendritic cells (rDCs) in the liver by LAP suppresses cytotoxic T-cell function and alleviates DEN-induced liver damage, fibrosis and tumorigenesis.

Hepatic inflammation is a defining feature of Metabolic Dysfunction-Associated Steatohepatitis (MASH), yet the specific contributions of individual immune cell populations and their reciprocal interactions remain incompletely understood. In this study, we combined flow cytometry with single-cell transcriptomic profiling to characterize the hepatic immune landscape in a novel model of spontaneous MASH caused by hepatocyte-specific deficiency of endoplasmic reticulum-associated degradation (ERAD). Hepatic ERAD deficiency led to the expansion of multiple immune cell populations in the liver, including CD8+ T cells, macrophages, monocytes, and dendritic cells, accompanied by extensive functional reprogramming of both innate and adaptive immune compartments. Myeloid cells exhibited enhanced phagocytic activity and increased antigen processing and presentation, whereas CD8+ T cells displayed elevated proliferation capacity, DNA repair activity and cytotoxicity. Notably, two functionally distinct triggering receptor expressed on myeloid cells 2 (TREM2)-expressing macrophage subsets emerged during the progression of ERAD deficiency-induced MASH. Depletion of CD8+ T cells increased monocyte infiltration and aggravated liver injury, suggesting that CD8+ T cells exert a previously unrecognized protective role by restraining monocyte recruitment. Collectively, these findings reveal highly coordinated interactions between innate and adaptive cells during MASH progression and identify CD8+ T cells as potential regulators of monocyte infiltration and hepatic injury.

Mitochondrial dysfunction has been associated with a variety of human diseases including neurodegeneration, diabetes, non-alcohol fatty liver disease (NAFLD) and cancer, but its underlying causes are incompletely understood. Endoplasmic reticular associated degradation (ERAD) is a protein quality control process essential for maintaining ER homeostasis. Using the human hepatic cell line HepG2 as a model, we show here that ERAD is critically required for mitochondrial function in mammalian cells. Pharmacological inhibition or genetic ablation of ERAD increases cell death under both basal conditions and in response to proinflammatory cytokines. Decreased viability of ERAD-deficient HepG2 cells was traced to impaired mitochondrial functions including reduced ATP production, enhanced reactive oxygen species (ROS) accumulation and increased mitochondrial outer membrane permeability (MOMP). Transcriptome profiling reveals widespread down-regulation in the expression of genes underpinning mitochondrial functions, and up-regulation in the genes with association to tumor growth and aggression. These results highlight a critical role for ERAD in maintaining mitochondrial functional and structural integrity and raise the possibility to improve cellular and organismal mitochondrial function via enhancing cellular ERAD capacity.