Magnesium accumulation upon cyclin M4 silencing activates microsomal triglyceride transfer protein improving NASH

Dimerization of the CNNM extracellular domain

Cystathionine-β $$ \beta $$ -synthase (CBS)-pair domain divalent metal cation transport mediators (CNNMs) are an evolutionarily conserved family of magnesium transporters. They mediate magnesium homeostasis directly by transport of Mg2+ ions and indirectly by regulation of the transient receptor potential ion channel subfamily M member 7 (TRPM7). Here, we report the crystal structure of the extracellular domain of tapeworm CNNM4. The domain forms a dimer of immunoglobulin-like (Ig-like) folds with electron density observed for three glycosylation sites. Analytical ultracentrifugation confirms that mutations in the extracellular domain of human CNNM4 prevent its dimerization. An analogous mutation in mouse CNNM2 impairs its activity in a cellular assay of Mg2+ transport.

New insights into the structure and function of CNNM proteins

Magnesium (Mg2+ ) is the most abundant divalent cation in cells and plays key roles in almost all biological processes. CBS-pair domain divalent metal cation transport mediators (CNNMs) are a newly characterized class of Mg2+ transporters present throughout biology. Originally discovered in bacteria, there are four CNNM proteins in humans, which are involved in divalent cation transport, genetic diseases, and cancer. Eukaryotic CNNMs are composed of four domains: an extracellular domain, a transmembrane domain, a cystathionine-β-synthase (CBS)-pair domain, and a cyclic nucleotide-binding homology domain. The transmembrane and CBS-pair core are the defining features of CNNM proteins with over 20 000 protein sequences known from over 8000 species. Here, we review the structural and functional studies of eukaryotic and prokaryotic CNNMs that underlie our understanding of their regulation and mechanism of ion transport. Recent structures of prokaryotic CNNMs confirm the transmembrane domain mediates ion transport with the CBS-pair domain likely playing a regulatory role through binding divalent cations. Studies of mammalian CNNMs have identified new binding partners. These advances are driving progress in understanding this deeply conserved and widespread family of ion transporters.

Ratiometric Fluorescent Sensors Illuminate Cellular Magnesium Imbalance in a Model of Acetaminophen-Induced Liver Injury

Magnesium(II) plays catalytic, structural, regulatory, and signaling roles in living organisms. Abnormal levels of this metal have been associated with numerous pathologies, including cardiovascular disease, diabetes, metabolic syndrome, immunodeficiency, cancer, and, most recently, liver pathologies affecting humans. The role of Mg2+ in the pathophysiology of liver disease, however, has been occluded by concomitant changes in concentration of interfering divalent cations, such as Ca2+, which complicates the interpretation of experiments conducted with existing molecular Mg2+ indicators. Herein, we introduce a new quinoline-based fluorescent sensor, MagZet1, that displays a shift in its excitation and emission wavelengths, affording ratiometric detection of cellular Mg2+ by both fluorescence microscopy and flow cytometry. The new sensor binds the target metal with a submillimolar dissociation constant─well suited for detection of changes in free Mg2+ in cells─and displays a 10-fold selectivity against Ca2+. Furthermore, the fluorescence ratio is insensitive to changes in pH in the physiological range, providing an overall superior performance over existing indicators. We provide insights into the metal selectivity profile of the new sensor based on computational modeling, and we apply it to shed light on a decrease in cytosolic free Mg2+ and altered expression of metal transporters in cellular models of drug-induced liver injury caused by acetaminophen overdose.

Essential metal mixtures exposure and NAFLD: A cohort-based case-control study in northern Chinese male adults

Epidemiologic evidence on metal mixtures and non-alcoholic fatty liver disease (NAFLD) is limited. We aimed to assess the relationship between multiple metal co-exposure and NAFLD among male adults in Northern China. We conducted a cohort-based case-control study with 648 NAFLD and 648 non-NAFLD males. Seven metal concentrations (calcium, copper, iron, magnesium, manganese, selenium, and zinc) were determined in the blood. We used logistic regression and restricted cubic splines (RCS) to estimate the associations between the single metal and NAFLD. The impact of metal mixtures was quantified by the environmental risk score (ERS) in the adaptive elastic-net regression, and the association with NAFLD was estimated by logistic regression. Age-adjusted RCS showed linear relationships between blood calcium, selenium, and NAFLD. Blood copper, iron, magnesium, and manganese were non-linearly associated with NAFLD. Single metal analysis observed significant relationships between calcium, copper, manganese, and NAFLD, with the adjusted odds ratio (95% confidence interval) for quartile 1 vs. quartile 4 of 1.99 (1.30, 3.05), 2.36 (1.52, 3.64), and 1.77 (1.22, 2.55), respectively. However, metal mixtures analysis revealed one squared term (copper [β = -0.146]) and five metal-metal interactions (calcium × copper [β = 0.200], copper × magnesium [β = 0.188], copper × selenium [β = 0.188], iron × magnesium [β = 0.143], magnesium × selenium [β = -0.297]) except the three main effects. Higher ERS indicated a higher risk for NAFLD when exposed to metal mixtures, with an adjusted odds ratio = 6.50 (95% confidence interval: 4.36-9.69) for quartile 4 vs. quartile 1. Mediation analysis suggested that 11.66% of the effect of ERS on NAFLD was suppressed by fasting blood glucose. Our results show that exposure to metal mixtures is associated with a higher risk for NAFLD than the single metal. Interactions between metals suggest the importance of balancing the various metals for health benefits. Prospective cohorts and mechanism studies need to confirm the findings.

Magnesium and Liver Metabolism Through the Lifespan

Within the organism, the liver is the main organ responsible for metabolic homeostasis and xenobiotic transformation. To maintain an adequate liver weight-to-bodyweight ratio, this organ has an extraordinary regenerative capacity and is able to respond to an acute insult or partial hepatectomy. Maintenance of hepatic homeostasis is crucial for the proper functioning of the liver, and in this context, adequate nutrition with macro- and micronutrient intake is mandatory. Among all known macro-minerals, magnesium has a key role in energy metabolism and in metabolic and signaling pathways that maintain liver function and physiology throughout its life span. In the present review, the cation is reported as a potential key molecule during embryogenesis, liver regeneration, and aging. The exact role of the cation during liver formation and regeneration is not fully understood due to its unclear role in the activation and inhibition of those processes, and further research in a developmental context is needed. As individuals age, they may develop hypomagnesemia, a condition that aggravates the characteristic alterations. Additionally, risk of developing liver pathologies increases with age, and hypomagnesemia may be a contributing factor. Therefore, magnesium loss must be prevented by adequate intake of magnesium-rich foods such as seeds, nuts, spinach, or rice to prevent age-related hepatic alterations and contribute to the maintenance of hepatic homeostasis. Since magnesium-rich sources include a variety of foods, a varied and balanced diet can meet both macronutrient and micronutrient needs.

Protective effects of the succinate/SUCNR1 axis on damaged hepatocytes in NAFLD

OBJECTIVE

Succinate and succinate receptor 1 (SUCNR1) are linked to fibrotic remodeling in models of non-alcoholic fatty liver disease (NAFLD), but whether they have roles beyond the activation of hepatic stellate cells remains unexplored. We investigated the succinate/SUCNR1 axis in the context of NAFLD specifically in hepatocytes.

METHODS

We studied the phenotype of wild-type and Sucnr1^-/- mice fed a choline-deficient high-fat diet to induce non-alcoholic steatohepatitis (NASH), and explored the function of SUCNR1 in murine primary hepatocytes and human HepG2 cells treated with palmitic acid. Lastly, plasma succinate and hepatic SUCNR1 expression were analyzed in four independent cohorts of patients in different NAFLD stages.

RESULTS

Sucnr1 was upregulated in murine liver and primary hepatocytes in response to diet-induced NASH. Sucnr1 deficiency provoked both beneficial (reduced fibrosis and endoplasmic reticulum stress) and detrimental (exacerbated steatosis and inflammation and reduced glycogen content) effects in the liver, and disrupted glucose homeostasis. Studies in vitro revealed that hepatocyte injury increased Sucnr1 expression, which when activated improved lipid and glycogen homeostasis in damaged hepatocytes. In humans, SUCNR1 expression was a good determinant of NAFLD progression to advanced stages. In a population at risk of NAFLD, circulating succinate was elevated in patients with a fatty liver index (FLI) ≥60. Indeed, succinate had good predictive value for steatosis diagnosed by FLI, and improved the prediction of moderate/severe steatosis through biopsy when added to an FLI algorithm.

CONCLUSIONS

We identify hepatocytes as target cells of extracellular succinate during NAFLD progression and uncover a hitherto unknown function for SUCNR1 as a regulator of hepatocyte glucose and lipid metabolism. Our clinical data highlight the potential of succinate and hepatic SUCNR1 expression as markers to diagnose fatty liver and NASH, respectively.

Interdisciplinary advances reshape the delivery tools for effective NASH treatment

BACKGROUND

Nonalcoholic steatohepatitis (NASH), a severe systemic and inflammatory subtype of nonalcoholic fatty liver disease, eventually develops into cirrhosis and hepatocellular carcinoma with few options for effective treatment. Currently potent small molecules identified in preclinical studies are confronted with adverse effects and long-term ineffectiveness in clinical trials. Nevertheless, highly specific delivery tools designed from interdisciplinary concepts may address the significant challenges by either effectively increasing the concentrations of drugs in target cell types, or selectively manipulating the gene expression in liver to resolve NASH.

SCOPE OF REVIEW

We focus on dissecting the detailed principles of the latest interdisciplinary advances and concepts that direct the design of future delivery tools to enhance the efficacy. Recent advances have indicated that cell and organelle-specific vehicles, non-coding RNA research (e.g. saRNA, hybrid miRNA) improve the specificity, while small extracellular vesicles and coacervates increase the cellular uptake of therapeutics. Moreover, strategies based on interdisciplinary advances drastically elevate drug loading capacity and delivery efficiency and ameliorate NASH and other liver diseases.

MAJOR CONCLUSIONS

The latest concepts and advances in chemistry, biochemistry and machine learning technology provide the framework and strategies for the design of more effective tools to treat NASH, other pivotal liver diseases and metabolic disorders.

Lanthanide-based luminescent probes for biological magnesium: accessing polyphosphate-bound Mg2

Biomolecule-bound Mg2+ species, particularly polyphosphate complexes, represent a large and dynamic fraction of the total cellular magnesium that is essential for cellular function but remains invisible to most indicators. Here we report a new family of Eu(III)-based indicators, the MagQEu family, functionalized with a 4-oxo-4H-quinolizine-3-carboxylic acid metal recognition group/sensitization antenna for turn-on, luminescence-based detection of biologically relevant Mg2+ species.

Magnesium reabsorption in the kidney

Mg²⁺ is essential for many cellular and physiological processes, including muscle contraction, neuronal activity, and metabolism. Consequently, the blood Mg²⁺ concentration is tightly regulated by balanced intestinal Mg²⁺ absorption, renal Mg²⁺ excretion, and Mg²⁺ storage in bone and soft tissues. In recent years, the development of novel transgenic animal models and identification of Mendelian disorders has advanced our current insight in the molecular mechanisms of Mg²⁺ reabsorption in the kidney. In the proximal tubule, Mg²⁺ reabsorption is dependent on paracellular permeability by claudin-2/12. In the thick ascending limb of Henle's loop, the claudin-16/19 complex provides a cation-selective pore for paracellular Mg²⁺ reabsorption. The paracellular Mg²⁺ reabsorption in this segment is regulated by the Ca²⁺-sensing receptor, parathyroid hormone, and mechanistic target of rapamycin (mTOR) signaling. In the distal convoluted tubule, the fine tuning of Mg²⁺ reabsorption takes place by transcellular Mg²⁺ reabsorption via transient receptor potential melastatin-like types 6 and 7 (TRPM6/TRPM7) divalent cation channels. Activity of TRPM6/TRPM7 is dependent on hormonal regulation, metabolic activity, and interacting proteins. Basolateral Mg²⁺ extrusion is still poorly understood but is probably dependent on the Na⁺ gradient. Cyclin M2 and SLC41A3 are the main candidates to act as Na⁺/Mg²⁺ exchangers. Consequently, disturbances of basolateral Na⁺/K⁺ transport indirectly result in impaired renal Mg²⁺ reabsorption in the distal convoluted tubule. Altogether, this review aims to provide an overview of the molecular mechanisms of Mg²⁺ reabsorption in the kidney, specifically focusing on transgenic mouse models and human hereditary diseases.

Restoring cellular magnesium balance through Cyclin M4 protects against acetaminophen-induced liver damage

Acetaminophen overdose is one of the leading causes of acute liver failure and liver transplantation in the Western world. Magnesium is essential in several cellular processess. The Cyclin M family is involved in magnesium transport across cell membranes. Herein, we identify that among all magnesium transporters, only Cyclin M4 expression is upregulated in the liver of patients with acetaminophen overdose, with disturbances in magnesium serum levels. In the liver, acetaminophen interferes with the mitochondrial magnesium reservoir via Cyclin M4, affecting ATP production and reactive oxygen species generation, further boosting endoplasmic reticulum stress. Importantly, Cyclin M4 mutant T495I, which impairs magnesium flux, shows no effect. Finally, an accumulation of Cyclin M4 in endoplasmic reticulum is shown under hepatoxicity. Based on our studies in mice, silencing hepatic Cyclin M4 within the window of 6 to 24 h following acetaminophen overdose ingestion may represent a therapeutic target for acetaminophen overdose induced liver injury.

Phosphatase-independent role of phosphatase of regenerating liver in cancer progression

Phosphatase of regenerating liver (PRL) is a family of protein tyrosine phosphatases (PTPs) that are anchored to the plasma membrane by prenylation. They are frequently overexpressed in various types of malignant cancers and their roles in cancer progression have received considerable attention. Mutational analyses of PRLs have shown that their intrinsic phosphatase activity is dispensable for tumor formation induced by PRL overexpression in a lung metastasis model using melanoma cells. Instead, PRLs directly bind to cyclin M (CNNM) Mg²⁺ exporters in the plasma membrane and potently inhibit their Mg²⁺ export activity, resulting in an increase in intracellular Mg²⁺ levels. Experiments using mammalian culture cells, mice, and C. elegans have collectively revealed that dysregulation of Mg²⁺ levels severely affects ATP and reactive oxygen species (ROS) levels as well as the function of Ca²⁺ -permeable channels. Moreover, PRL overexpression altered the optimal pH for cell proliferation from normal 7.5 to acidic 6.5, which is typically observed in malignant tumors. Here, we review the phosphatase-independent biological functions of PRLs, focusing on their interactions with CNNM Mg²⁺ exporters in cancer progression.

Mouse models of nonalcoholic fatty liver disease (NAFLD): pathomechanisms and pharmacotherapies

The prevalence of non-alcoholic fatty liver disease (NAFLD) increases year by year, and as a consequence, NAFLD has become one of the most prevalent liver diseases worldwide. Unfortunately, no pharmacotherapies for NAFLD have been approved by the United States Food and Drug Administration despite promising pre-clinical benefits; this situation highlights the urgent need to explore new therapeutic targets for NAFLD and for the discovery of effective therapeutic drugs. The mouse is one of the most commonly used models to study human disease and develop novel pharmacotherapies due to its small size, low-cost and ease in genetic engineering. Different mouse models are used to simulate various stages of NAFLD induced by dietary and/or genetic intervention. In this review, we summarize the newly described patho-mechanisms of NAFLD and review the preclinical mouse models of NAFLD (based on the method of induction) and appraises the use of these models in anti-NAFLD drug discovery. This article will provide a useful resource for researchers to select the appropriate model for research based on the research question being addressed.

Indole supplementation ameliorates MCD-induced NASH in mice

Indole is a microbiota metabolite that functions to protect against obesity-associated non-alcoholic fatty liver disease. The present study examined the extent to which indole supplementation alleviates the severity of non-alcoholic steatohepatitis (NASH), which is the advanced form of non-alcoholic fatty liver disease. In C57BL/6J mice, feeding a methionine- and choline-deficient diet (MCD) resulted in significant weight loss, overt hepatic steatosis, and massive aggregations of macrophages in the liver compared with control diet-fed mice. Upon indole supplementation, the severity of MCD-induced hepatic steatosis and inflammation, as well as liver fibrosis, was significantly decreased compared with that of MCD-fed and control-treated mice. In vitro, indole treatment caused significant decreases in lipopolysaccharide-induced proinflammatory responses in hepatocytes incubated with either basal or MCD-mimicking media. However, indole treatment only significantly decreased lipopolysaccharide-induced proinflammatory responses in bone marrow-derived macrophages incubated with basal, but not MCD-mimicking media. These differential effects suggest that, relative to the responses of macrophages to indole, the responses of hepatocytes to indole appeared to make a greater contribution to indole alleviation of NASH, in particular liver inflammation. While indole supplementation decreased liver expression of desmin in MCD-fed mice, treatment of LX2 cells (a line of hepatic stellate cells) with indole also decreased the expression of various markers of hepatic stellate cell fibrogenic activation. Lastly, indole supplementation decreased intestinal inflammation in MCD-fed mice, suggesting that decreased intestinal inflammation also was involved in indole alleviation of NASH. Collectively, these results demonstrate that indole supplementation alleviates MCD-induced NASH, which is attributable to, in large part, indole suppression of hepatocyte proinflammatory responses and hepatic stellate cell fibrogenic activation, as well as intestinal proinflammatory responses.

The spike of SARS-CoV-2 promotes metabolic rewiring in hepatocytes

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a multi-organ damage that includes hepatic dysfunction, which has been observed in over 50% of COVID-19 patients. Liver injury in COVID-19 could be attributed to the cytopathic effects, exacerbated immune responses or treatment-associated drug toxicity. Herein we demonstrate that hepatocytes are susceptible to infection in different models: primary hepatocytes derived from humanized angiotensin-converting enzyme-2 mice (hACE2) and primary human hepatocytes. Pseudotyped viral particles expressing the full-length spike of SARS-CoV-2 and recombinant receptor binding domain (RBD) bind to ACE2 expressed by hepatocytes, promoting metabolic reprogramming towards glycolysis but also impaired mitochondrial activity. Human and hACE2 primary hepatocytes, where steatosis and inflammation were induced by methionine and choline deprivation, are more vulnerable to infection. Inhibition of the renin-angiotensin system increases the susceptibility of primary hepatocytes to infection with pseudotyped viral particles. Metformin, a common therapeutic option for hyperglycemia in type 2 diabetes patients known to partially attenuate fatty liver, reduces the infection of human and hACE2 hepatocytes. In summary, we provide evidence that hepatocytes are amenable to infection with SARS-CoV-2 pseudovirus, and we propose that metformin could be a therapeutic option to attenuate infection by SARS-CoV-2 in patients with fatty liver.

SARS-CoV-2 pseudovirus infects human hepatocytes leading to metabolic reprogramming towards glycolysis and impaired mitochondrial activity, and metformin can reduce infection under steatotic conditions.

Risk Factors and Prediction Models for Nonalcoholic Fatty Liver Disease Based on Random Forest

Objective

To establish a risk prediction model of nonalcoholic fatty liver disease (NAFLD) and provide management strategies for preventing this disease.

Methods

A total of 200 inpatients and physical examinees were collected from the Department of Gastroenterology and Endocrinology and Physical Examination Center. The data of physical examination, laboratory examination, and abdominal ultrasound examination were collected. All subjects were randomly divided into a training set (70%) and a verification set (30%). A random forest (RF) prediction model is constructed to predict the occurrence risk of NAFLD. The receiver operating characteristic (ROC) curve is used to verify the prediction effect of the prediction models.

Results

The number of NAFLD patients was 44 out of 200 enrolled patients, and the cumulative incidence rate was 22%. The prediction models showed that BMI, TG, HDL-C, LDL-C, ALT, SUA, and MTTP mutations were independent influencing factors of NAFLD, all of which has statistical significance (P < 0.05). The area under curve (AUC) of logistic regression and the RF model was 0.940 (95% CI: 0.870~0.987) and 0.945 (95% CI: 0.899~0.994), respectively.

Conclusion

This study established a prediction model of NAFLD occurrence risk based on the RF, which has a good prediction value.

CNNM proteins selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells

Magnesium is essential for cellular life, but how it is homeostatically controlled still remains poorly understood. Here, we report that members of CNNM family, which have been controversially implicated in both cellular Mg²⁺ influx and efflux, selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells. Coexpression of CNNMs with the channel markedly increased uptake of divalent cations, which is prevented by an inactivating mutation to the channel’s pore. Knockout (KO) of TRPM7 in cells or application of the TRPM7 channel inhibitor NS8593 also interfered with CNNM-stimulated divalent cation uptake. Conversely, KO of CNNM3 and CNNM4 in HEK-293 cells significantly reduced TRPM7-mediated divalent cation entry, without affecting TRPM7 protein expression or its cell surface levels. Furthermore, we found that cellular overexpression of phosphatases of regenerating liver (PRLs), known CNNMs binding partners, stimulated TRPM7-dependent divalent cation entry and that CNNMs were required for this activity. Whole-cell electrophysiological recordings demonstrated that deletion of CNNM3 and CNNM4 from HEK-293 cells interfered with heterologously expressed and native TRPM7 channel function. We conclude that CNNMs employ the TRPM7 channel to mediate divalent cation influx and that CNNMs also possess separate TRPM7-independent Mg²⁺ efflux activities that contribute to CNNMs’ control of cellular Mg²⁺ homeostasis.

Magnesium is essential for cellular life, but how is it homeostatically controlled? This study shows that proteins of the CNNM family bind to the TRPM7 channel to stimulate divalent cation entry into cells, independent of their function in regulating magnesium ion efflux.

Antioxidant support to ameliorate the oxaliplatin-dependent microglial alteration: morphological and molecular study

Oxaliplatin is a third-generation chemotherapy drug mainly used for colorectal cancer treatment. However, it is also known to trigger neuropathy whose underlying neurobiological mechanisms are still under investigation and currently available treatments show limited efficacy. It is now established that neurons are not the only cell type involved in chronic pain and that glial cells, mainly astrocytes and microglia, are involved in the initiation and maintenance of neuropathy. Among all the pathogenetic factors involved in neuropathic pain, an oxaliplatin-dependent oxidative stress plays a predominant role. In our study, the antioxidant properties of magnesium (Mg), manganese (Mn) and zinc (Zn) salts were evaluated in order to counteract microglial activation induced by oxaliplatin. The antioxidant efficacy of these metals was evaluated by the means of molecular and morphological assays on the BV-2 microglial cell line. Our data clearly show that Mg, Mn and Zn are able to prevent oxaliplatin-dependent microglial alterations by reducing both oxidative and endoplasmic reticulum stress.

Crystal structure of an archaeal CorB magnesium transporter

CNNM/CorB proteins are a broadly conserved family of integral membrane proteins with close to 90,000 protein sequences known. They are associated with Mg²⁺ transport but it is not known if they mediate transport themselves or regulate other transporters. Here, we determine the crystal structure of an archaeal CorB protein in two conformations (apo and Mg²⁺-ATP bound). The transmembrane DUF21 domain exists in an inward-facing conformation with a Mg²⁺ ion coordinated by a conserved π-helix. In the absence of Mg²⁺-ATP, the CBS-pair domain adopts an elongated dimeric configuration with previously unobserved domain-domain contacts. Hydrogen-deuterium exchange mass spectrometry, analytical ultracentrifugation, and molecular dynamics experiments support a role of the structural rearrangements in mediating Mg²⁺-ATP sensing. Lastly, we use an in vitro, liposome-based assay to demonstrate direct Mg²⁺ transport by CorB proteins. These structural and functional insights provide a framework for understanding function of CNNMs in Mg²⁺ transport and associated diseases.