Deep proteomic profiling unveils arylsulfatase A as a non-alcoholic steatohepatitis inducible hepatokine and regulator of glycemic control

Sulfation pathways in the maintenance of functional beta-cell mass and implications for diabetes

Diabetes Type 1 and Type 2 are widely occurring diseases. In spite of a vast amount of biomedical literature about diabetic processes in general, links to certain biological processes are only becoming evident these days. One such area of biology is the sulfation of small molecules, such as steroid hormones or metabolites from the gastrointestinal tract, as well as larger biomolecules, such as proteins and proteoglycans. Thus, modulating the physicochemical propensities of the different sulfate acceptors, resulting in enhanced solubility, expedited circulatory transit, or enhanced macromolecular interaction. This review lists evidence for the involvement of sulfation pathways in the maintenance of functional pancreatic beta-cell mass and the implications for diabetes, grouped into various classes of sulfated biomolecule. Complex heparan sulfates might play a role in the development and maintenance of beta-cells. The sulfolipids sulfatide and sulfo-cholesterol might contribute to beta-cell health. In beta-cells, there are only very few proteins with confirmed sulfation on some tyrosine residues, with the IRS4 molecule being one of them. Sulfated steroid hormones, such as estradiol-sulfate and vitamin-D-sulfate, may facilitate downstream steroid signaling in beta-cells, following de-sulfation. Indoxyl sulfate is a metabolite from the intestine, that causes kidney damage, contributing to diabetic kidney disease. Finally, from a technological perspective, there is heparan sulfate, heparin, and chondroitin sulfate, that all might be involved in next-generation beta-cell transplantation. Sulfation pathways may play a role in pancreatic beta-cells through multiple mechanisms. A more coherent understanding of sulfation pathways in diabetes will facilitate discussion and guide future research.

Single-base tiled screen unveils design principles of PspCas13b for potent and off-target-free RNA silencing

The development of precise RNA-editing tools is essential for the advancement of RNA therapeutics. CRISPR (clustered regularly interspaced short palindromic repeats) PspCas13b is a programmable RNA nuclease predicted to offer superior specificity because of its 30-nucleotide spacer sequence. However, its design principles and its on-target, off-target and collateral activities remain poorly characterized. Here, we present single-base tiled screening and computational analyses that identify key design principles for potent and highly selective RNA recognition and cleavage in human cells. We show that the de novo design of spacers containing guanosine bases at precise positions can greatly enhance the catalytic activity of inefficient CRISPR RNAs (crRNAs). These validated design principles (integrated into an online tool, https://cas13target.azurewebsites.net/ ) can predict highly effective crRNAs with ~90% accuracy. Furthermore, the comprehensive spacer-target mutagenesis revealed that PspCas13b can tolerate only up to four mismatches and requires ~26-nucleotide base pairing with the target to activate its nuclease domains, highlighting its superior specificity compared to other RNA or DNA interference tools. On the basis of this targeting resolution, we predict an extremely low probability of PspCas13b having off-target effects on other cellular transcripts. Proteomic analysis validated this prediction and showed that, unlike other Cas13 orthologs, PspCas13b exhibits potent on-target activity and lacks collateral effects.

Targeting hepatic ceruloplasmin mitigates nonalcoholic steatohepatitis by modulating bile acid metabolism

Nonalcoholic steatohepatitis (NASH) is a condition that progresses from nonalcoholic fatty liver disease (NAFLD) and is characterized by hepatic fat accumulation, inflammation, and fibrosis. It has the potential to develop into cirrhosis and liver cancer, and currently no effective pharmacological treatment is available. In this study, we investigate the therapeutic potential of targeting ceruloplasmin (Cp), a copper-containing protein predominantly secreted by hepatocytes, for treating NASH. Our result show that hepatic Cp is remarkedly upregulated in individuals with NASH and the mouse NASH model. Hepatocyte-specific Cp ablation effectively attenuates the onset of dietary-induced NASH by decreasing lipid accumulation, curbing inflammation, mitigating fibrosis, and ameliorating liver damage. By employing transcriptomics and metabolomics approaches, we have discovered that hepatic deletion of Cp brings about remarkable restoration of bile acid (BA) metabolism during NASH. Hepatic deletion of Cp effectively remodels BA metabolism by upregulating Cyp7a1 and Cyp8b1, which subsequently leads to enhanced BA synthesis and notable alterations in BA profiles. In conclusion, our studies elucidate the crucial involvement of Cp in NASH, highlighting its significance as a promising therapeutic target for the treatment of this disease.

Fetuin B in white adipose tissue induces inflammation and is associated with peripheral insulin resistance in mice and humans

OBJECTIVE

Fetuin B is a steatosis-responsive hepatokine that causes glucose intolerance in mice, but the underlying mechanisms remain incompletely described. This study aimed to elucidate the mechanisms of action of fetuin B by investigating its putative effects on white adipose tissue metabolism.

METHODS

First, fetuin B gene and protein expression was measured in multiple organs in mice and in cultured adipocytes. Next, the authors performed a hyperinsulinemic-euglycemic clamp in mice and in humans to examine the link between white adipose tissue fetuin B content and indices of insulin sensitivity. Finally, the effect of fetuin B on inflammation was investigated in cultured adipocytes by quantitative polymerase chain reaction and full RNA sequencing.

RESULTS

This study demonstrated in adipocytes and mice that fetuin B was produced and secreted by the liver and taken up by adipocytes and adipose tissue. There was a strong negative correlation between white adipose tissue fetuin B content and peripheral insulin sensitivity in mice and in humans. RNA sequencing and polymerase chain reaction analysis revealed that fetuin B induced an inflammatory response in adipocytes.

CONCLUSIONS

Fetuin B content in white adipose tissue strongly associated with peripheral insulin resistance in mice and humans. Furthermore, fetuin B induced a proinflammatory response in adipocytes, which might drive peripheral insulin resistance.

Drug targets regulate systemic metabolism and provide new horizons to treat nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH), is the advanced stage of nonalcoholic fatty liver disease (NAFLD) with rapidly rising global prevalence. It is featured with severe hepatocyte apoptosis, inflammation and hepatic lipogenesis. The drugs directly targeting the processes of steatosis, inflammation and fibrosis are currently under clinical investigation. Nevertheless, the long-term ineffectiveness and remarkable adverse effects are well documented, and new concepts are required to tackle with the root causes of NASH progression. We critically assess the recently validated drug targets that regulate the systemic metabolism to ameliorate NASH. Thermogenesis promoted by mitochondrial uncouplers restores systemic energy expenditure. Furthermore, regulation of mitochondrial proteases and proteins that are pivotal for intracellular metabolic homeostasis normalize mitochondrial function. Secreted proteins also improve systemic metabolism, and NASH is ameliorated by agonizing receptors of secreted proteins with small molecules. We analyze the drug design, the advantages and shortcomings of these novel drug candidates. Meanwhile, the structural modification of current NASH therapeutics significantly increased their selectivity, efficacy and safety. Furthermore, the arising CRISPR-Cas9 screen strategy on liver organoids has enabled the identification of new genes that mediate lipid metabolism, which may serve as promising drug targets. In summary, this article discusses the in-depth novel mechanisms and the multidisciplinary approaches, and they provide new horizons to treat NASH.

Liver-derived extracellular vesicles improve whole-body glycaemic control via inter-organ communication

Small extracellular vesicles (EVs) are signalling messengers that regulate inter-tissue communication through delivery of their molecular cargo. Here, we show that liver-derived EVs are acute regulators of whole-body glycaemic control in mice. Liver EV secretion into the circulation is increased in response to hyperglycaemia, resulting in increased glucose effectiveness and insulin secretion through direct inter-organ EV signalling to skeletal muscle and the pancreas, respectively. This acute blood glucose lowering effect occurs in healthy and obese mice with non-alcoholic fatty liver disease, despite marked remodelling of the liver-derived EV proteome in obese mice. The EV-mediated blood glucose lowering effects were recapitulated by administration of liver EVs derived from humans with or without progressive non-alcoholic fatty liver disease, suggesting broad functional conservation of liver EV signalling and potential therapeutic utility. Taken together, this work reveals a mechanism whereby liver EVs act on peripheral tissues via endocrine signalling to restore euglycaemia in the postprandial state.

Hibernation and plasma lipids in free-ranging brown bears-implications for diabetes

Brown bears (Ursus arctos) prepare for winter by overeating and increasing adipose stores, before hibernating for up to six months without eating, drinking, and with minimal movement. In spring, the bears exit the den without any damage to organs or physiology. Recent clinical research has shown that specific lipids and lipid profiles are of special interest for diseases such as diabetes type 1 and 2. Furthermore, rodent experiments show that lipids such as sulfatide protects rodents against diabetes. As free-ranging bears experience fat accumulation and month-long physical inactivity without developing diabetes, they could possibly be affected by similar protective measures. In this study, we investigated whether lipid profiles of brown bears are related to protection against hibernation-induced damage. We sampled plasma from 10 free-ranging Scandinavian brown bears during winter hibernation and repeated sampling during active state in the summer period. With quantitative shotgun lipidomics and liquid chromatography-mass spectrometry, we profiled 314 lipid species from 26 lipid classes. A principal component analysis revealed that active and hibernation samples could be distinguished from each other based on their lipid profiles. Six lipid classes were significantly altered when comparing plasma from active state and hibernation: Hexosylceramide, phosphatidylglycerol, and lysophosphatidylglycerol were higher during hibernation, while phosphatidylcholine ether, phosphatidylethanolamine ether, and phosphatidylinositol were lower. Additionally, sulfatide species with shorter chain lengths were lower, while longer chain length sulfatides were higher during hibernation. Lipids that are altered in bears are described by others as relevant for and associated with diabetes, which strengthens their position as potential effectors during hibernation. From this analysis, a range of lipids are suggested as potential protectors of bear physiology, and of potential importance in diabetes.

Exercise training induces depot-specific remodeling of protein secretion in skeletal muscle and adipose tissue of obese male mice

Acute exercise induces changes in circulating proteins, which are known to alter metabolism and systemic energy balance. Skeletal muscle is a primary contributor to changes in the plasma proteome with acute exercise. An important consideration when assessing the endocrine function of muscle is the presence of different fiber types, which show distinct functional and metabolic properties and likely secrete different proteins. Similarly, adipokines are important regulators of systemic metabolism and have been shown to differ between depots. Given the health-promoting effects of exercise, we proposed that understanding depot-specific remodeling of protein secretion in muscle and adipose tissue would provide new insights into intertissue communication and uncover novel regulators of energy homeostasis. Here, we examined the effect of endurance exercise training on protein secretion from fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscle and visceral and subcutaneous adipose tissue. High-fat diet-fed mice were exercise trained for 6 wk, whereas a Control group remained sedentary. Secreted proteins from excised EDL and soleus muscle, inguinal, and epididymal adipose tissues were detected using mass spectrometry. We detected 575 and 784 secreted proteins from EDL and soleus muscle and 738 and 920 proteins from inguinal and epididymal adipose tissue, respectively. Of these, 331 proteins were secreted from all tissues, whereas secretion of many other proteins was tissue and depot specific. Exercise training led to substantial remodeling of protein secretion from EDL, whereas soleus showed only minor changes. Myokines released exclusively from EDL or soleus were associated with glycogen metabolism and cellular stress response, respectively. Adipokine secretion was completely refractory to exercise regulation in both adipose depots. This study provides an in-depth resource of protein secretion from muscle and adipose tissue, and its regulation following exercise training, and identifies distinct depot-specific secretion patterns that are related to the metabolic properties of the tissue of origin.NEW & NOTEWORTHY The present study examines the effects of exercise training on protein secretion from fast-twitch and slow-twitch muscle as well as visceral and subcutaneous adipose tissue of obese mice. Although exercise training leads to substantial remodeling of protein secretion from fast-twitch muscle, adipose tissue is completely refractory to exercise regulation.

Environmental exposures are important risk factors for advanced liver fibrosis in African American adults

Background & Aims

The prevalence and aetiology of liver fibrosis vary over time and impact racial/ethnic groups unevenly. This study measured time trends and identified factors associated with advanced liver fibrosis in the United States.

Methods

Standardised methods were used to analyse data on 47,422 participants (≥20 years old) in the National Health and Nutrition Examination Survey (1999-2018). Advanced liver fibrosis was defined as Fibrosis-4 ≥2.67 and/or Forns index ≥6.9 and elevated alanine aminotransferase.

Results

The estimated number of people with advanced liver fibrosis increased from 1.3 million (95% CI 0.8-1.9) to 3.5 million (95% CI 2.8-4.2), a nearly threefold increase. Prevalence was higher in non-Hispanic Black and Mexican American persons than in non-Hispanic White persons. In multivariable logistic regression analysis, cadmium was an independent risk factor in all racial/ethnic groups. Smoking and current excessive alcohol use were risk factors in most. Importantly, compared with non-Hispanic White persons, non-Hispanic Black persons had a distinctive set of risk factors that included poverty (odds ratio [OR] 2.09; 95% CI 1.44-3.03) and susceptibility to lead exposure (OR 3.25; 95% CI 1.95-5.43) but did not include diabetes (OR 0.88; 95% CI 0.61-1.27; p =0.52). Non-Hispanic Black persons were more likely to have high exposure to lead, cadmium, polychlorinated biphenyls, and poverty than non-Hispanic White persons.

Conclusions

The number of people with advanced liver fibrosis has increased, creating a need to expand the liver care workforce. The risk factors for advanced fibrosis vary by race/ethnicity. These differences provide useful information for designing screening programmes. Poverty and toxic exposures were associated with the high prevalence of advanced liver fibrosis in non-Hispanic Black persons and need to be addressed.

Impact and Implications

Because liver disease often produces few warning signs, simple and inexpensive screening tests that can be performed by non-specialists are needed to allow timely diagnosis and linkage to care. This study shows that non-Hispanic Black persons have a distinctive set of risk factors that need to be taken into account when designing liver disease screening programs. Exposure to exogenous toxins may be especially important risk factors for advanced liver fibrosis in non-Hispanic Black persons.

Relationship of Sulfatides Physiological Function and Peroxisome Proliferator-Activated Receptor α

Sulfatides are unique sphingolipids present in the serum and the plasma membrane. Sulfatides exert important functions in a number of systems in the human body, including the nervous, immune, cardiovascular, and coagulation systems.Furthermore, it is closely related to tumor occurrence, development, and metastasis. Peroxisome proliferators-activated receptor α (PPARα) is a class of the nuclear receptor superfamily of transcription factors, which is a potential regulator of sulfatides. This review not only summarizes the current knowledge on the physiological functions of sulfatides in various systems, but also discusses the possible PPARα regulatory mechanisms in sulfatide metabolism and functions. The results of the present analysis provide deep insights and further novel ideas for expanding the research on the physiological function and clinical application of sulfatides.

Investigating dual inhibition of ACC and CD36 for the treatment of nonalcoholic fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. Dysregulation in hepatic lipid metabolism, including increased fatty acid uptake and de novo lipogenesis (DNL), is a hallmark of NAFLD. Here, we investigated dual inhibition of the fatty acid transporter fatty acid translocase (FAT/CD36), and acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in DNL, for the treatment of NAFLD in mice. Mice with hepatic CD36 deletion (Cd36^LKO) and wild-type littermates were fed a high-fat diet for 12 wk and treated daily with either oral administration of an ACC inhibitor (GS-834356, Gilead Sciences; ACCi) or vehicle for 8 wk. Neither CD36 deletion or ACC inhibition impacted body composition, energy expenditure, or glucose tolerance. Cd36^LKO mice had elevated fasting plasma insulin, suggesting mild insulin resistance. Whole body fatty acid oxidation was significantly decreased in Cd36^LKO mice. Liver triglyceride content was significantly reduced in mice treated with ACCi; however, CD36 deletion caused an unexpected increase in liver triglycerides. This was associated with upregulation of genes and proteins of DNL, including ACC, and decreased liver triglyceride secretion ex vivo. Overall, these data confirm the therapeutic utility of ACC inhibition for steatosis resolution but indicate that inhibition of CD36 is not an effective treatment for NAFLD in mice.NEW & NOTEWORTHY Dysregulation of hepatic lipid metabolism is a hallmark of nonalcoholic fatty liver disease. Here, we show that dual inhibition of the de novo lipogenesis enzyme, ACC, and hepatic deletion of the fatty acid transporter, CD36, was ineffective for the treatment of NAFLD in mice. This was due to a paradoxical increase in liver triglycerides with CD36 deletion resulting from decreased hepatic triglyceride secretion and increased lipogenic gene expression.

Liver Protein Expression in NASH Mice on a High-Fat Diet: Response to Multi-Mineral Intervention

Male MS-NASH mice were maintained on a high-fat diet for 16 weeks with and without red algae-derived minerals. Obeticholic acid (OCA) was used as a comparator in the same strain and diet. C57BL/6 mice maintained on a standard (low-fat) rodent chow diet were used as a control. At the end of the in-life portion of the study, body weight, liver weight, liver enzyme levels and liver histology were assessed. Samples obtained from individual livers were subjected to Tandem Mass Tag labeling / mass spectroscopy for protein profile determination. As compared to mice maintained on the low-fat diet, all high-fat-fed mice had increased whole-body and liver weight, increased liver enzyme (aminotransferases) levels and widespread steatosis / ballooning hepatocyte degeneration. Histological evidence for liver inflammation and collagen deposition was also present, but changes were to a lesser extent. A moderate reduction in ballooning degeneration and collagen deposition was observed with mineral supplementation. Control mice on the high-fat diet alone demonstrated multiple protein changes associated with dysregulated fat and carbohydrate metabolism, lipotoxicity and oxidative stress. Cholesterol metabolism and bile acid formation were especially sensitive to diet. In mice receiving multi-mineral supplementation along with the high-fat diet, there was reduced liver toxicity as evidenced by a decrease in levels of several cytochrome P450 enzymes and other oxidant-generating moieties. Additionally, elevated expression of several keratins was also detected in mineral-supplemented mice. The protein changes observed with mineral supplementation were not seen with OCA. Our previous studies have shown that mice maintained on a high-fat diet for up to 18 months develop end-stage liver injury including hepatocellular carcinoma. Mineral-supplemented mice were substantially protected against tumor formation and other end-state consequences of high-fat feeding. The present study identifies early (16-week) protein changes occurring in the livers of the high-fat diet-fed mice, and how the expression of these proteins is influenced by mineral supplementation. These findings help elucidate early protein changes that contribute to end-stage liver injury and potential mechanisms by which dietary minerals may mitigate such damage.

Proteomic analysis reveals exercise training induced remodelling of hepatokine secretion and uncovers syndecan-4 as a regulator of hepatic lipid metabolism

Objective

Non-alcoholic fatty liver disease (NAFLD) is linked to impaired lipid metabolism and systemic insulin resistance, which is partly mediated by altered secretion of liver proteins known as hepatokines. Regular physical activity can resolve NAFLD and improve its metabolic comorbidities, however, the effects of exercise training on hepatokine secretion and the metabolic impact of exercise-regulated hepatokines in NAFLD remain unresolved. Herein, we examined the effect of endurance exercise training on hepatocyte secreted proteins with the aim of identifying proteins that regulate metabolism and reduce NAFLD severity.

Methods

C57BL/6 mice were fed a high-fat diet for six weeks to induce NAFLD. Mice were exercise trained for a further six weeks, while the control group remained sedentary. Hepatocytes were isolated two days after the last exercise bout, and intracellular and secreted proteins were detected using label-free mass spectrometry. Hepatocyte secreted factors were applied to skeletal muscle and liver ex vivo and insulin action and fatty acid metabolism were assessed. Syndecan-4 (SDC4), identified as an exercise-responsive hepatokine, was overexpressed in the livers of mice using adeno-associated virus. Whole-body energy homeostasis was assessed by indirect calorimetry and skeletal muscle and liver metabolism was assessed using radiometric techniques.

Results

Proteomics analysis detected 2657 intracellular and 1593 secreted proteins from mouse hepatocytes. Exercise training remodelled the hepatocyte proteome, with differences in 137 intracellular and 35 secreted proteins. Bioinformatic analysis of hepatocyte secreted proteins revealed enrichment of tumour suppressive proteins and proteins involved in lipid metabolism and mitochondrial function, and suppression of oncogenes and regulators of oxidative stress. Hepatocyte secreted factors from exercise trained mice improved insulin action in skeletal muscle and increased hepatic fatty acid oxidation. Hepatocyte-specific overexpression of SDC4 reduced hepatic steatosis, which was associated with reduced hepatic fatty acid uptake, and blunted pro-inflammatory and pro-fibrotic gene expression. Treating hepatocytes with recombinant ectodomain of SDC4 (secreted form) recapitulated these effects with reduced fatty acid uptake, lipid storage and lipid droplet accumulation.

Conclusions

Remodelling of hepatokine secretion is an adaptation to regular exercise training that induces changes in metabolism in the liver and skeletal muscle. SDC4 is a novel exercise-responsive hepatokine that decreases fatty acid uptake and reduces steatosis in the liver. By understanding the proteomic changes in hepatocytes with exercise, these findings have potential for the discovery of new therapeutic targets for NAFLD.

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Exercise training remodels hepatokine secretion.

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Exercise regulated secreted factors improve insulin action in skeletal muscle.

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Syndecan-4 (SDC4) is a novel exercise-induced hepatokine.

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SDC4 reduces hepatic fatty acid uptake and hepatic steatosis.