The Slc25a47 locus is a novel determinant of hepatic mitochondrial function implicated in liver fibrosis

The Role of Solute Carrier Family Transporters in Hepatic Steatosis and Hepatic Fibrosis

Solute carrier (SLC) family transporters are crucial transmembrane proteins responsible for transporting various molecules, including amino acids, electrolytes, fatty acids, and nucleotides. To date, more than fifty SLC transporter subfamilies have been identified, many of which are linked to the progression of hepatic steatosis and fibrosis. These conditions are often caused by factors such as non-alcoholic fatty liver disease and non-alcoholic steatohepatitis, which are major contributors to the global liver disease burden. The activity of SLC members regulates the transport of substrates across biological membranes, playing key roles in lipid synthesis and metabolism, mitochondrial function, and ferroptosis. These processes, in turn, influence the function of hepatocytes, hepatic stellate cells, and macrophages, thereby contributing to the development of hepatic steatosis and fibrosis. Additionally, some SLC transporters are involved in drug transport, acting as critical regulators of drug-induced hepatic steatosis. Beyond substrate transport, certain SLC members also exhibit additional functions. Given the pivotal role of the SLC family in hepatic steatosis and fibrosis, this review aimed to summarize the molecular mechanisms through which SLC transporters influence these conditions.

Hepatotoxicity Reduction Profiles of Antisense Oligonucleotides Containing Amido-Bridged Nucleic Acid and 2'-O,4'-C-Spirocyclopropylene Bridged Nucleic Acid

Amido-bridged nucleic acid (AmNA) and a 2'-O,4'-C-spirocyclopropylene bridged nucleic acid (scpBNA) are bridged nucleic acid analogs with high binding affinity toward complementary strands along with high nuclease resistance. AmNA and scpBNA have been developed to overcome phosphorothioate modified gapmer hepatotoxicity, while the mechanism of reducing hepatotoxicity still remains unknown. Here, we found that antisense oligonucleotides (ASOs) with combination of AmNA, scpBNA, and phosphodiester (PO) bonds could significantly reduce hepatotoxicity in mice. Histopathological findings of the periportal spaces of the liver were observed only in the locked nucleic acid and AmNA-scpBNA groups, but not in the AmNA-scpBNA-PO group. Furthermore, bioinformatics and histopathological analysis revealed that the reduced hepatotoxicity might be related to mitochondrial abnormalities, such as decreased expression levels of Atp5o and Sdhb genes. Taken together, the results of this study demonstrated that AmNA, scpBNA, and PO modification are able to reduce hepatotoxicity for improving the potential of ASOs.

RNA-seq analysis reveals transcriptome changes in livers from Efcab4b knockout mice

EFCAB4B is an evolutionarily conserved protein that encodes for the Rab GTPase Rab46, and the CRAC channel modulator, CRACR2A. Previous genome wide association studies have demonstrated the association of EFCAB4B variants in the progression of non-alcoholic fatty liver disease (NAFLD). In this study we show that mice with global depletion of Efcab4b -/- have significantly larger livers than their wild-type (WT) counterparts. We performed RNA-sequencing (RNA-seq) analysis of liver tissues to investigate differential global gene expression among Efcab4b -/- and WT mice. Of the 69 differentially expressed genes (DEGs), analyses of biological processes found significant enrichment in liver and bile development, with 6 genes (Pck1, Aacs, Onecut1, E2f8, Xbp1, and Hes1) involved in both processes. Specific consideration of possible roles of DEGs or their products in NAFLD progression to (NASH) and hepatocarcinoma (HCC), demonstrated DEGs in the livers of Efcab4b -/- mice had roles in molecular pathways including lipid metabolism, inflammation, ER stress and fibrosis. The results in this study provide additional insights into molecular mechanisms responsible for increasing susceptibility of liver injuries associated with EFCAB4B.

miR-361-5p regulates SLC25A24 to maintain mitochondrial function and alleviate granulosa cell dysfunction in diminished ovarian reserve

BACKGROUND

The aim of this study was to investigate the role of miR-361-5p (a tumor suppressor) in regulating granulosa cell function by targeting SLC25A24, a key mitochondrial protein, to uncover potential therapeutic targets for diminished ovarian reserve (DOR).

METHODS

This study included patients undergoing assisted reproductive technology treatment at our hospital. Granulosa cells were isolated from follicular fluid, and KGN cells were used for in vitro experiments. miR-361-5p and SLC25A24 expression levels were manipulated using miRNA mimics and inhibitors, and their effects on cell viability, apoptosis, and mitochondrial function were assessed. Techniques employed included qRT-PCR, Western blot analysis, ELISA, JC-1 staining, and dual-luciferase reporter assays. Key quantitative metrics included changes in mitochondrial DNA (mtDNA), ATP production, and reactive oxygen species (ROS) levels.

RESULTS

miR-361-5p expression was significantly lower in DOR patients' granulosa cells compared to controls (P < 0.01). miR-361-5p inhibition markedly decreased KGN cells viability and increased apoptosis (P < 0.01), while miR-361-5p overexpression had the opposite effects (P < 0.01). SLC25A24 expression was inversely correlated with miR-361-5p levels, and its knockdown reversed the effects of miR-361-5p inhibition. Additionally, miR-361-5p modulation significantly affected mitochondrial function, with its overexpression reducing ROS levels and increasing ATP production (P < 0.01).

CONCLUSION

miR-361-5p plays a pivotal role in maintaining mitochondrial function and reducing KGN cells dysfunction by targeting SLC25A24. These findings offer new insights into the molecular mechanisms of DOR and highlight miR-361-5p as a potential therapeutic target to enhance ovarian reserve and improve fertility outcomes.

Deficiency of the mitochondrial transporter SLC25A47 minimally impacts hepatic lipid metabolism in fasted and diet-induced obese mice

OBJECTIVE

The peroxisome proliferator-activated receptor-alpha (PPARα) plays a central role in lipid metabolism in the liver by stimulating the expression of hundreds of genes. Accordingly, regulation by PPARα could be a screening tool to identify novel genes involved in hepatic lipid metabolism. Previously, the mitochondrial transporter SLC25A47 was suggested to play a role in energy metabolism and liver-specific uncoupling, but further research is lacking.

METHODS

We explored the potential role of SLC25A47 through in vitro studies and using mice overexpressing and lacking SLC25A47.

RESULTS

SLC25A47 was identified as a PPARα-regulated and fasting-induced gene in human and mouse hepatocytes. Adenoviral-mediated overexpression of SLC25A47 minimally impacted metabolic parameters during fasting and high-fat feeding. During high-fat feeding, SLC25A47 ablation also did not influence any metabolic parameters, apart from a minor improvement in glucose tolerance. In fasted mice, SLC25A47 ablation was associated with modest, reproducible, and likely indirect reductions in plasma triglycerides and glycerol. SLC25A47 ablation did not influence energy expenditure. Depending on the nutritional status, metabolomic analysis showed modest alterations in plasma, liver, and hepatic mitochondrial levels of various metabolites related to amino acid metabolism, TCA cycle, and fatty acid metabolism. No major and consistent alterations in levels of specific metabolites were found that establish the substrate for and function of SLC25A47.

CONCLUSION

Collectively, our results hint at a role of SLC25A47 in amino acid and fatty acid metabolism, yet suggest that SLC25A47 is dispensable for hepatic lipid homeostasis during fasting and high-fat feeding.

Metabolic changes during evolution of Sjögren's in both an animal model and human patients

Sjögren's (SS) involves salivary and lacrimal gland dysfunction. These studies examined metabolic profiles in the B6. Il14α transgene mouse model of SS and a cohort of human SS patients at different stages of disease. In B6. Il14α mice, products of glucose and fatty acid were common at 6 months of age, while products of amino acid metabolism were common at 12 months of age. Treating B6. Il14α mice with the glycolysis inhibitor 2-deoxyglucose from 6 to 10 months of age normalized salivary gland secretions, dacryoadenitis, hypergammaglobulinemia and physical performance, while treatment from 10 to 14 months of age failed to improve any of the clinical manifestations. Similarly, SS patients at an early stage of disease showed high glycolysis. SS patients with long-standing disease utilized predominantly amino acid metabolism, like B6. Il14α mice at 10-12 months of age. Additional studies are suggested to further define metabolic activities at the various disease stages.

The impact of solute carrier proteins on disrupting substance regulation in metabolic disorders: insights and clinical applications

Carbohydrates, lipids, bile acids, various inorganic salt ions and organic acids are the main nutrients or indispensable components of the human body. Dysregulation in the processes of absorption, transport, metabolism, and excretion of these metabolites can lead to the onset of severe metabolic disorders, such as type 2 diabetes, non-alcoholic fatty liver disease, gout and hyperbilirubinemia. As the second largest membrane receptor supergroup, several major families in the solute carrier (SLC) supergroup have been found to play key roles in the transport of substances such as carbohydrates, lipids, urate, bile acids, monocarboxylates and zinc ions. Based on common metabolic dysregulation and related metabolic substances, we explored the relationship between several major families of SLC supergroup and metabolic diseases, providing examples of drugs targeting SLC proteins that have been approved or are currently in clinical/preclinical research as well as SLC-related diagnostic techniques that are in clinical use or under investigation. By highlighting these connections, we aim to provide insights that may contribute to the development of improved treatment strategies and targeted therapies for metabolic disorders.

Wars1 downregulation in hepatocytes induces mitochondrial stress and disrupts metabolic homeostasis

Several laboratories, including ours, have employed the Slc25a47tm1c(EUCOMM)Hmgu mouse model to investigate the role of SLC25A47, a hepatocyte-specific mitochondrial carrier, in regulating hepatic metabolism and systemic physiology. In this study, we reveal that the hepatic and systemic phenotypes observed following recombination of the Slc25a47-Wars1 locus in hepatocytes are primarily driven by the unexpected downregulation of Wars1, the cytosolic tryptophan aminoacyl-tRNA synthetase located adjacent to Slc25a47. While the downregulation of Wars1 predictably affects cytosolic translation, we also observed a significant impairment in mitochondrial protein synthesis within hepatocytes. This disturbance in mitochondrial function leads to an activation of the mitochondrial unfolded protein response (UPRmt), a critical component of the mitochondrial stress response (MSR). Our findings clarify the distinct roles of Slc25a47 and Wars1 in maintaining both systemic and hepatic metabolic homeostasis. This study sheds new light on the broader implications of aminoacyl-tRNA synthetases in mitochondrial physiology and stress responses.

Cell metabolism-based therapy for liver fibrosis, repair, and hepatocellular carcinoma

Progression of chronic liver injury to fibrosis, abnormal liver regeneration, and HCC is driven by a dysregulated dialog between epithelial cells and their microenvironment, in particular immune, fibroblasts, and endothelial cells. There is currently no antifibrogenic therapy, and drug treatment of HCC is limited to tyrosine kinase inhibitors and immunotherapy targeting the tumor microenvironment. Metabolic reprogramming of epithelial and nonparenchymal cells is critical at each stage of disease progression, suggesting that targeting specific metabolic pathways could constitute an interesting therapeutic approach. In this review, we discuss how modulating intrinsic metabolism of key effector liver cells might disrupt the pathogenic sequence from chronic liver injury to fibrosis/cirrhosis, regeneration, and HCC.

Mitochondrial heterogeneity and adaptations to cellular needs

Although it is well described that mitochondria are at the epicentre of the energy demands of a cell, it is becoming important to consider how each cell tailors its mitochondrial composition and functions to suit its particular needs beyond ATP production. Here we provide insight into mitochondrial heterogeneity throughout development as well as in tissues with specific energy demands and discuss how mitochondrial malleability contributes to cell fate determination and tissue remodelling.

Human umbilical cord-derived mesenchymal stem cells ameliorate liver fibrosis by improving mitochondrial function via Slc25a47-Sirt3 signaling pathway

Chronic Liver fibrosis may progress to liver cirrhosis and hepatocellular carcinoma (HCC), hence cause a substantial global burden. However, effective therapies for blocking fibrosis are still lacking. Although mesenchymal stem cells (MSCs) have been proven beneficial to liver regeneration after damage, the underlying mechanism of their therapeutic effects are not fully understood. Oxidative stress and mitochondrial functionality alteration directly contributes to the hepatocyte apoptosis and development of liver fibrosis. This study aims to elucidate the mechanism by which hUC-MSC alleviates liver fibrosis and mitochondrial dysfunction. RNA-sequencing was performed to characterize the transcriptomic changes after implantation of hUC-MSCs in mice with liver fibrosis. Next, western blot, RT-PCR, immunohistochemical and immunofluorescence staining were used to evaluate the expression of different genes in vitro and in vivo. Additionally, mitochondrial morphological and dynamic changes, ROS content, and ATP production were examined. Slc25a47, a newly identified liver-specific mitochondrial NAD+ transporter, was notably reduced in CCl4-treated mice and H2O2-stimulated hepatocytes. Conversely, hUC-MSCs increased the Slc25a47 expression and NAD+ level within mitochondria, thereby enhanced Sirt3 protein activity and alleviated mitochondrial dysfunction in the liver. Furthermore, Slc25a47 knockdown could partially abrogate the protective effects of hUC-MSCs on H2O2-induced mitochondrial fission and oxidative stress in hepatocytes. Our study illustrates that Slc25a47 is a key molecular for hUC-MSCs to improve liver fibrosis and regulates mitochondrial function through Sirt3 for the first time, and providing a theoretical basis for the clinical translation of hUC-MSCs transplantation in the treatment of patients with liver fibrosis/cirrhosis.

Mtfp1 ablation enhances mitochondrial respiration and protects against hepatic steatosis

Hepatic steatosis is the result of imbalanced nutrient delivery and metabolism in the liver and is the first hallmark of Metabolic dysfunction-associated steatotic liver disease (MASLD). MASLD is the most common chronic liver disease and involves the accumulation of excess lipids in hepatocytes, inflammation, and cancer. Mitochondria play central roles in liver metabolism yet the specific mitochondrial functions causally linked to MASLD remain unclear. Here, we identify Mitochondrial Fission Process 1 protein (MTFP1) as a key regulator of mitochondrial and metabolic activity in the liver. Deletion of Mtfp1 in hepatocytes is physiologically benign in mice yet leads to the upregulation of oxidative phosphorylation (OXPHOS) activity and mitochondrial respiration, independently of mitochondrial biogenesis. Consequently, liver-specific knockout mice are protected against high fat diet-induced steatosis and metabolic dysregulation. Additionally, Mtfp1 deletion inhibits mitochondrial permeability transition pore opening in hepatocytes, conferring protection against apoptotic liver damage in vivo and ex vivo. Our work uncovers additional functions of MTFP1 in the liver, positioning this gene as an unexpected regulator of OXPHOS and a therapeutic candidate for MASLD.

Mitochondrial oxidative stress regulates LonP1-TDP-43 pathway and rises mitochondrial damage in carbon tetrachloride-induced liver fibrosis

Carbon tetrachloride (CCl4)-mediated liver damage has been well recognized, but the sources and mechanisms of mitochondrial damage during this progress still remain poorly understood. Accumulating evidence has revealed that LonP1-TDP-43 pathway affect proper mitochondrial integrity and function in neurodegenerative diseases. The current study aims to investigate whether mitochondrial oxidative stress regulate LonP1-TDP-43 pathway and the possible roles of this pathway in CCl4-driven liver fibrosis. We found that TDP-43 interacted with LonP1 in chronic CCl4 exposure-induced hepatic fibrogenesis. Moreover, CCl4 led to deficiency of LonP1 and excessive accumulation of TDP-43 on mitochondria. Particularly, the gene correlation analysis for liver fibrosis patients RNA sequencing (RNA-seq) results (GSE159676) showed an obvious negative correlation between LonP1 and TDP-43. By contrast, MitoQ enhanced the occurrence of mitochondrial unfolded protein response (mtUPR), especially the activation of LonP1 after CCl4 treatment. Importantly, mitochondrial antioxidant also promoted the degradation of TDP-43 and alleviated mitochondrial damage. In addition, our results showed that CCl4 induced the release of mitochondrial DNA (mtDNA) and effectively elevated cGAS-STING-mediated immune response, which can be inhibited by MitoQ. Finally, MitoQ prevented CCl4-induced liver fibrosis. Together, our study revealed that LonP1-TDP-43 pathway mediated by mitochondrial oxidative stress participated in the progress of CCl4-drived liver fibrosis. Therefore, mitigating or reversing mitochondrial damage through targeting LonP1-TDP-43 pathway may serve as a promising therapeutic strategy for CCl4 exposure-induced liver diseases.

Cyclo(His-Pro): A further step in the management of steatohepatitis

Background & Aims

Non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) have become the world's most common liver diseases, placing a growing strain on healthcare systems worldwide. Nonetheless, no effective pharmacological treatment has been approved. The naturally occurring compound cyclo histidine-proline (His-Pro) (CHP) is an interesting candidate for NAFLD management, given its safety profile and anti-inflammatory effects.

Methods

Two different mouse models of liver disease were used to evaluate protective effects of CHP on disease progression towards fibrosis: a model of dietary NAFLD/NASH, achieved by thermoneutral housing (TN) in combination with feeding a western diet (WD), and liver fibrosis caused by repeated injections with carbon tetrachloride (CCl4).

Results

Treatment with CHP limited overall lipid accumulation, lowered systemic inflammation, and prevented hyperglycaemia. Histopathology and liver transcriptomics highlighted reduced steatosis and demonstrated remarkable protection from the development of inflammation and fibrosis, features which herald the progression of NAFLD. We identified the extracellular signal-regulated kinase (ERK) pathway as an early mediator of the cellular response to CHP.

Conclusions

CHP was active in both the preventive and therapeutic setting, reducing liver steatosis, fibrosis, and inflammation and improving several markers of liver disease.

Impact and implications

Considering the incidence and the lack of approved treatments, it is urgent to identify new strategies that prevent and manage NAFLD. CHP was effective in attenuating NAFLD progression in two animal models of the disease. Overall, our work points to CHP as a novel and effective strategy for the management of NAFLD, fuelling optimism for potential clinical studies.

Phylogenetic Analysis Guides Transporter Protein Deorphanization: A Case Study of the SLC25 Family of Mitochondrial Metabolite Transporters

Homology search and phylogenetic analysis have commonly been used to annotate gene function, although they are prone to error. We hypothesize that the power of homology search in functional annotation depends on the coupling of sequence variation to functional diversification, and we herein focus on the SoLute Carrier (SLC25) family of mitochondrial metabolite transporters to survey this coupling in a family-wide manner. The SLC25 family is the largest family of mitochondrial metabolite transporters in eukaryotes that translocate ligands of different chemical properties, ranging from nucleotides, amino acids, carboxylic acids and cofactors, presenting adequate experimentally validated functional diversification in ligand transport. Here, we combine phylogenetic analysis to profile SLC25 transporters across common eukaryotic model organisms, from Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, Danio rerio, to Homo sapiens, and assess their sequence adaptations to the transported ligands within individual subfamilies. Using several recently studied and poorly characterized SLC25 transporters, we discuss the potentials and limitations of phylogenetic analysis in guiding functional characterization.

The GCKR-P446L gene variant predisposes to raised blood cholesterol and lower blood glucose in the P446L mouse-a model for GCKR rs1260326

OBJECTIVES

The Glucokinase Regulatory Protein GKRP, encoded by GCKR, enables acute regulation of liver glucokinase to support metabolic demand. The common human GCKR rs1260326:Pro446 > Leu variant within a large linkage disequilibrium region associates with pleiotropic traits including lower Type 2 diabetes risk and raised blood triglycerides and cholesterol. Whether the GCKR-P446 > L substitution is causal to the raised lipids is unknown. We determined whether mouse GKRP phenocopies the human GKRP:P446 > L substitution and studied a GKRP:P446L knockin mouse to identify physiological consequences to P446 > L.

METHODS

GKRP-deficient hepatocytes were transfected with adenoviral vectors for human or mouse GKRP:446 P or 446 L for cellular comprehensive analysis including transcriptomics consequent to P446 > L. Physiological traits in the diet-challenged P446L mouse were compared with pleiotropic associations at the human rs1260326 locus. Transcriptomics was compared in P446L mouse liver with hepatocytes overexpressing glucokinase or GKRP:446 P/L.

RESULTS

1. P446 > L substitution in mouse or human GKRP similarly compromises protein expressivity of GKRP:446 L, nuclear sequestration of glucokinase and counter-regulation of gene expression. 2. The P446L knockin mouse has lower liver glucokinase and GKRP protein similar to human liver homozygous for rs1260326-446 L. 3. The diet-challenged P446L mouse has lower blood glucose, raised blood cholesterol and altered hepatic cholesterol homeostasis consistent with relative glucokinase-to-GKRP excess, but not raised blood triglycerides.

CONCLUSIONS

Mouse GKRP phenocopies the human GKRP:P446 > L substitution despite the higher affinity for glucokinase of human GKRP. The diet-challenged P446L mouse replicates several traits found in association with the rs1260326 locus on chromosome 2 including raised blood cholesterol, lower blood glucose and lower liver glucokinase and GKRP protein but not raised blood triglycerides.

New insights into the bile acid-based regulatory mechanisms and therapeutic perspectives in alcohol-related liver disease

Cholestasis is a key causative factor in alcohol-related liver disease (ALD) and variable degrees of cholestasis occur in all stages of ALD. However, the pathogenetic mechanisms and biomarkers associated with cholestasis are not well characterized. Cholestatic disease is marked by the disruption of bile acids (BA) transport and homeostasis. Consequently, in both human and experimental ALD, the disease shows a direct correlation with an imbalance in BA equilibrium, which in turn may also affect the severity of the disease. Modulation of BA metabolism or signaling pathways is increasingly considered as a potential therapeutic strategy for ALD in humans. In this paper, we highlight the key advances made in the past two decades in characterizing the molecular regulatory mechanisms of BA synthesis, enterohepatic circulation, and BA homeostasis. We summarize recent insights into the nature of the linkage between BA dysregulation and ALD, including the abnormal expression of genes involved in BA metabolism, abnormal changes in receptors that regulate BA metabolism, and disturbance in the gut flora engaged in BA metabolism caused by alcohol consumption. Additionally, we provide novel perspectives on the changes in BAs in various stages of ALD. Finally, we propose potential pharmacological therapies for ALD targeting BA metabolism and signaling.