The Functions of SARS-CoV-2 Receptors in Diabetes-Related Severe COVID-19

Angiotensin-converting enzyme 2 (ACE2) is considered a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor of high importance, but due to its non-ubiquitous expression, studies of other proteins that may participate in virus internalisation have been undertaken. To date, many alternative receptors have been discovered. Their functioning may provide an explanation for some of the events observed in severe COVID-19 that cannot be directly explained by the model in which ACE2 constitutes the central point of infection. Diabetes mellitus type 2 (T2D) can induce severe COVID-19 development. Although many mechanisms associated with ACE2 can lead to increased SARS-CoV-2 virulence in diabetes, proteins such as basigin (CD147), glucose-regulated protein 78 kDa (GRP78), cluster of differentiation 4 (CD4), transferrin receptor (TfR), integrins α5β1/αvβ3, or ACE2 co-receptors neuropilin 2 (NRP2), vimentin, and even syalilated gangliosides may also be responsible for worsening the COVID-19 course. On the other hand, some others may play protective roles. Understanding how diabetes-associated mechanisms can induce severe COVID-19 via modification of virus receptor functioning needs further extensive studies.

Multi-Omics Analysis Revealed the rSNPs Potentially Involved in T2DM Pathogenic Mechanism and Metformin Response

The goal of our study was to identify and assess the functionally significant SNPs with potentially important roles in the development of type 2 diabetes mellitus (T2DM) and/or their effect on individual response to antihyperglycemic medication with metformin. We applied a bioinformatics approach to identify the regulatory SNPs (rSNPs) associated with allele-asymmetric binding and expression events in our paired ChIP-seq and RNA-seq data for peripheral blood mononuclear cells (PBMCs) of nine healthy individuals. The rSNP outcomes were analyzed using public data from the GWAS (Genome-Wide Association Studies) and Genotype-Tissue Expression (GTEx). The differentially expressed genes (DEGs) between healthy and T2DM individuals (GSE221521), including metformin responders and non-responders (GSE153315), were searched for in GEO RNA-seq data. The DEGs harboring rSNPs were analyzed using the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). We identified 14,796 rSNPs in the promoters of 5132 genes of human PBMCs. We found 4280 rSNPs to associate with both phenotypic traits (GWAS) and expression quantitative trait loci (eQTLs) from GTEx. Between T2DM patients and controls, 3810 rSNPs were detected in the promoters of 1284 DEGs. Based on the protein-protein interaction (PPI) network, we identified 31 upregulated hub genes, including the genes involved in inflammation, obesity, and insulin resistance. The top-ranked 10 enriched KEGG pathways for these hubs included insulin, AMPK, and FoxO signaling pathways. Between metformin responders and non-responders, 367 rSNPs were found in the promoters of 131 DEGs. Genes encoding transcription factors and transcription regulators were the most widely represented group and many were shown to be involved in the T2DM pathogenesis. We have formed a list of human rSNPs that add functional interpretation to the T2DM-association signals identified in GWAS. The results suggest candidate causal regulatory variants for T2DM, with strong enrichment in the pathways related to glucose metabolism, inflammation, and the effects of metformin.

DNA Methylation-derived biological age and long-term mortality risk in subjects with type 2 diabetes

BACKGROUND

Individuals with type 2 diabetes (T2D) face an increased mortality risk, not fully captured by canonical risk factors. Biological age estimation through DNA methylation (DNAm), i.e. the epigenetic clocks, is emerging as a possible tool to improve risk stratification for multiple outcomes. However, whether these tools predict mortality independently of canonical risk factors in subjects with T2D is unknown.

METHODS

Among a cohort of 568 T2D patients followed for 16.8 years, we selected a subgroup of 50 subjects, 27 survived and 23 deceased at present, passing the quality check and balanced for all risk factors after propensity score matching. We analyzed DNAm from peripheral blood leukocytes using the Infinium Human MethylationEPIC BeadChip (Illumina) to evaluate biological aging through previously validated epigenetic clocks and assess the DNAm-estimated levels of selected inflammatory proteins and blood cell counts. We tested the associations of these estimates with mortality using two-stage residual-outcome regression analysis, creating a reference model on data from the group of survived patients.

RESULTS

Deceased subjects had higher median epigenetic age expressed with DNAmPhenoAge algorithm (57.49 [54.72; 60.58] years. vs. 53.40 [49.73; 56.75] years; p = 0.012), and accelerated DunedinPoAm pace of aging (1.05 [1.02; 1.11] vs. 1.02 [0.98; 1.06]; p = 0.012). DNAm PhenoAge (HR 1.16, 95% CI 1.05-1.28; p = 0.004) and DunedinPoAm (HR 3.65, 95% CI 1.43-9.35; p = 0.007) showed an association with mortality independently of canonical risk factors. The epigenetic predictors of 3 chronic inflammation-related proteins, i.e. CXCL10, CXCL11 and enRAGE, C-reactive protein methylation risk score and DNAm-based estimates of exhausted CD8 + T cell counts were higher in deceased subjects when compared to survived.

CONCLUSIONS

These findings suggest that biological aging, as estimated through existing epigenetic tools, is associated with mortality risk in individuals with T2D, independently of common risk factors and that increased DNAm-surrogates of inflammatory protein levels characterize deceased T2D patients. Replication in larger cohorts is needed to assess the potential of this approach to refine mortality risk in T2D.

Differential Roles of Interleukin-6 in Severe Acute Respiratory Syndrome-Coronavirus-2 Infection and Cardiometabolic Diseases

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection can lead to a cytokine storm, unleashed in part by pyroptosis of virus-infected macrophages and monocytes. Interleukin-6 (IL-6) has emerged as a key participant in this ominous complication of COVID-19. IL-6 antagonists have improved outcomes in patients with COVID-19 in some, but not all, studies. IL-6 signaling involves at least 3 distinct pathways, including classic-signaling, trans-signaling, and trans-presentation depending on the localization of IL-6 receptor and its binding partner glycoprotein gp130. IL-6 has become a therapeutic target in COVID-19, cardiovascular diseases, and other inflammatory conditions. However, the efficacy of inhibition of IL-6 signaling in metabolic diseases, such as obesity and diabetes, may depend in part on cell type-dependent actions of IL-6 in controlling lipid metabolism, glucose uptake, and insulin sensitivity owing to complexities that remain to be elucidated. The present review sought to summarize and discuss the current understanding of how and whether targeting IL-6 signaling ameliorates outcomes following SARS-CoV-2 infection and associated clinical complications, focusing predominantly on metabolic and cardiovascular diseases.

Endothelial ADAM17 Expression in the Progression of Kidney Injury in an Obese Mouse Model of Pre-Diabetes

Disintegrin and metalloproteinase domain 17 (ADAM17) activates inflammatory and fibrotic processes through the shedding of various molecules such as Tumor Necrosis Factor-α (TNF-α) or Transforming Growht Factor-α (TGF-α). There is a well-recognised link between TNF-α, obesity, inflammation, and diabetes. In physiological situations, ADAM17 is expressed mainly in the distal tubular cell while, in renal damage, its expression increases throughout the kidney including the endothelium. The aim of this study was to characterize, for the first time, an experimental mouse model fed a high-fat diet (HFD) with a specific deletion of Adam17 in endothelial cells and to analyse the effects on different renal structures. Endothelial Adam17 knockout male mice and their controls were fed a high-fat diet, to induce obesity, or standard rodent chow, for 22 weeks. Glucose tolerance, urinary albumin-to-creatinine ratio, renal histology, macrophage infiltration, and galectin-3 levels were evaluated. Results showed that obese mice presented higher blood glucose levels, dysregulated glucose homeostasis, and higher body weight compared to control mice. In addition, obese wild-type mice presented an increased albumin-to-creatinine ratio; greater glomerular size and mesangial matrix expansion; and tubular fibrosis with increased galectin-3 expression. Adam17 deletion decreased the albumin-to-creatinine ratio, glomerular mesangial index, and tubular galectin-3 expression. Moreover, macrophage infiltration in the glomeruli of obese Adam17 knockout mice was reduced as compared to obese wild-type mice. In conclusion, the expression of ADAM17 in endothelial cells impacted renal inflammation, modulating the renal function and histology in an obese pre-diabetic mouse model.

Redefining the Role of ADAM17 in Renal Proximal Tubular Cells and Its Implications in an Obese Mouse Model of Pre-Diabetes

Acute and chronic kidney lesions induce an increase in A Disintegrin And Metalloproteinase domain 17 (ADAM17) that cleaves several transmembrane proteins related to inflammatory and fibrotic pathways. Our group has demonstrated that renal ADAM17 is upregulated in diabetic mice and its inhibition decreases renal inflammation and fibrosis. The purpose of the present study was to analyze how Adam17 deletion in proximal tubules affects different renal structures in an obese mice model. Tubular Adam17 knockout male mice and their controls were fed a high-fat diet (HFD) for 22 weeks. Glucose tolerance, urinary albumin-to-creatinine ratio, renal histology, and pro-inflammatory and pro-fibrotic markers were evaluated. Results showed that wild-type mice fed an HFD became obese with glucose intolerance and renal histological alterations mimicking a pre-diabetic condition; consequently, greater glomerular size and mesangial expansion were observed. Adam17 tubular deletion improved glucose tolerance and protected animals against glomerular injury and prevented podocyte loss in HFD mice. In addition, HFD mice showed more glomerular macrophages and collagen accumulation, which was prevented by Adam17 deletion. Galectin-3 expression increased in the proximal tubules and glomeruli of HFD mice and ameliorated with Adam17 deletion. In conclusion, Adam17 in proximal tubules influences glucose tolerance and participates in the kidney injury in an obese pre-diabetic murine model. The role of ADAM17 in the tubule impacts on glomerular inflammation and fibrosis.

Lower miR-26a levels in breastmilk affect gene expression in adipose tissue of offspring

Breastmilk miRNAs may act as epigenetic regulators of metabolism and energy homeostasis in offspring. Here, we aimed to investigate the regulatory effects of miR-26a on adipose tissue development. First, the 3T3-L1 cell model was used to identify putative target genes for miR-26a. Then, target genes were analysed in adipose tissue of offspring from dams that supplied lower levels of breastmilk miR-26a to determine whether miR-26a milk concentration might have a long-lasting impact on adipose tissue in the progeny. In the in vitro model, both over- and under-expression of miR-26a were induced by transfecting into 3T3-L1 with miR-26a mimic and inhibitor. Array analysis was performed after induction of miR-26a to ascertain the impact on mRNA target genes and influence of differentiation status. Focusing on genes related to adipose tissue development, transfection with miR-26a mimic reduced the expression of Pten, Hmga1, Stk11, Rb1, and Adam17 in both pre- and mature adipocytes. Data mostly confirmed the results found in the animal model. After weaning, descendants of cafeteria-fed dams breastfed with lower levels of miR-26a displayed greater expression of Hmag1, Rb1, and Adam17 in retroperitoneal white adipose tissue in comparison with controls. Hence, alterations in the amount of miR-26a supplied through milk during lactation is able to alter the expression of target genes in the descendants and may affect adipose tissue development. Thus, milk miR-26a may act as an epigenetic regulator influencing early metabolic program in the progeny, which emerges as a relevant component of an optimal milk composition for correct development.

Implications of ADAM17 activation for hyperglycaemia, obesity and type 2 diabetes

In this review, we focus specifically on the role that the metalloproteinase, A Disintegrin and Metalloproteinase 17 [ADAM17] plays in the development and progression of the metabolic syndrome. There is a well-recognised link between the ADAM17 substrate tumour necrosis factor α (TNF-α) and obesity, inflammation and diabetes. In addition, knocking out ADAM17 in mice leads to an extremely lean phenotype. Importantly, ADAM17-deficient mice exhibit one of the most pronounced examples of hypermetabolism in rodents to date. It is vital to further understand the mechanistic role that ADAM17 plays in the metabolic syndrome. Such studies will demonstrate that ADAM17 is a valuable therapeutic target to treat obesity and diabetes.

Contribution of ADAM17 and related ADAMs in cardiovascular diseases

A disintegrin and metalloproteases (ADAMs) are key mediators of cell signaling by ectodomain shedding of various growth factors, cytokines, receptors and adhesion molecules at the cellular membrane. ADAMs regulate cell proliferation, cell growth, inflammation, and other regular cellular processes. ADAM17, the most extensively studied ADAM family member, is also known as tumor necrosis factor (TNF)-α converting enzyme (TACE). ADAMs-mediated shedding of cytokines such as TNF-α orchestrates immune system or inflammatory cascades and ADAMs-mediated shedding of growth factors causes cell growth or proliferation by transactivation of the growth factor receptors including epidermal growth factor receptor. Therefore, increased ADAMs-mediated shedding can induce inflammation, tissue remodeling and dysfunction associated with various cardiovascular diseases such as hypertension and atherosclerosis, and ADAMs can be a potential therapeutic target in these diseases. In this review, we focus on the role of ADAMs in cardiovascular pathophysiology and cardiovascular diseases. The main aim of this review is to stimulate new interest in this area by highlighting remarkable evidence.

Deletion of iRhom2 protects against diet-induced obesity by increasing thermogenesis

Objective

Obesity is the result of positive energy balance. It can be caused by excessive energy consumption but also by decreased energy dissipation, which occurs under several conditions including when the development or activation of brown adipose tissue (BAT) is impaired. Here we evaluated whether iRhom2, the essential cofactor for the Tumour Necrosis Factor (TNF) sheddase ADAM17/TACE, plays a role in the pathophysiology of metabolic syndrome.

Methods

We challenged WT versus iRhom2 KO mice to positive energy balance by chronic exposure to a high fat diet and then compared their metabolic phenotypes. We also carried out ex vivo assays with primary and immortalized mouse brown adipocytes to establish the autonomy of the effect of loss of iRhom2 on thermogenesis and respiration.

Results

Deletion of iRhom2 protected mice from weight gain, dyslipidemia, adipose tissue inflammation, and hepatic steatosis and improved insulin sensitivity when challenged by a high fat diet. Crucially, the loss of iRhom2 promotes thermogenesis via BAT activation and beige adipocyte recruitment, enabling iRhom2 KO mice to dissipate excess energy more efficiently than WT animals. This effect on enhanced thermogenesis is cell-autonomous in brown adipocytes as iRhom2 KOs exhibit elevated UCP1 levels and increased mitochondrial proton leak.

Conclusion

Our data suggest that iRhom2 is a negative regulator of thermogenesis and plays a role in the control of adipose tissue homeostasis during metabolic disease.

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Deletion of iRhom2 protects mice from metabolic syndrome.

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In obesity, iRhom2 deletion increases energy expenditure, thermogenesis and white adipose tissue beiging.

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iRhom2 deletion enhances thermogenesis in naïve brown adipocytes.

A Reduction in ADAM17 Expression Is Involved in the Protective Effect of the PPAR-α Activator Fenofibrate on Pressure Overload-Induced Cardiac Hypertrophy

The peroxisome proliferator-activated receptor-α (PPAR-α) agonist fenofibrate ameliorates cardiac hypertrophy; however, its mechanism of action has not been completely determined. Our previous study indicated that a disintegrin and metalloproteinase-17 (ADAM17) is required for angiotensin II-induced cardiac hypertrophy. This study aimed to determine whether ADAM17 is involved in the protective action of fenofibrate against cardiac hypertrophy. Abdominal artery constriction- (AAC-) induced hypertensive rats were used to observe the effects of fenofibrate on cardiac hypertrophy and ADAM17 expression. Primary cardiomyocytes were pretreated with fenofibrate (10 μM) for 1 hour before being stimulated with angiotensin II (100 nM) for another 24 hours. Fenofibrate reduced the ratios of left ventricular weight to body weight (LVW/BW) and heart weight to body weight (HW/BW), left ventricular anterior wall thickness (LVAW), left ventricular posterior wall thickness (LVPW), and ADAM17 mRNA and protein levels in left ventricle in AAC-induced hypertensive rats. Similarly, in vitro experiments showed that fenofibrate significantly attenuated angiotensin II-induced cardiac hypertrophy and diminished ADAM17 mRNA and protein levels in primary cardiomyocytes stimulated with angiotensin II. In summary, a reduction in ADAM17 expression is associated with the protective action of PPAR-α agonists against pressure overload-induced cardiac hypertrophy.

A Disintegrin and Metalloprotease 17 in the Cardiovascular and Central Nervous Systems

ADAM17 is a metalloprotease and disintegrin that lodges in the plasmatic membrane of several cell types and is able to cleave a wide variety of cell surface proteins. It is somatically expressed in mammalian organisms and its proteolytic action influences several physiological and pathological processes. This review focuses on the structure of ADAM17, its signaling in the cardiovascular system and its participation in certain disorders involving the heart, blood vessels, and neural regulation of autonomic and cardiovascular modulation.

Daily exercise training protects against albuminuria and angiotensin converting enzyme 2 shedding in db/db diabetic mice

Angiotensin II (Ang II) is involved in induction and progression of renal damage in diabetes. Angiotensin converting enzyme 2 (ACE2) is highly expressed in the kidney and has been shown to be renoprotective by degrading Ang II to Ang-(1-7). A disintegrin and metalloproteinase 17 (ADAM17)-mediated shedding of renal ACE2 contribute to diabetic nephropathy pathogenesis. Lifestyle modification and metformin are recommended as initial therapies for most patients with type 2 diabetes. The aim of this study was to investigate whether exercise training and/or metformin improve glucose homeostasis and albuminuria and downregulate renal ADAM17 and ACE2 shedding in db/db mice. Seven-week-old normal and db/db mice were subjected either to a sedentary existence or exercise training with and without metformin (150 mg/kg per day) for 10 weeks. Exercise training significantly lowered blood glucose, urinary albumin and ACE2 excretion in db/db mice. ADAM17 and ACE2 proteins were co-localized in cortical tubules of the kidney, indicating a possible interaction. Metformin treatment was effective in lowering hyperglycemia only during the first 2 weeks of treatment. Increased renal ADAM17 in 17-week-old db/db mice was corrected by physical exercise but not metformin. In addition, exercise training reduced plasma triglycerides and enhanced insulin levels of db/db mice. In conclusion, exercise training alone and in combination with metformin prevented shedding of renal ACE2 by decreasing ADAM17 protein. Urinary ACE2 could serve as a prognostic tool for the progression of kidney damage and its attenuation by exercise may partially contribute to its renal protection.

Significance of AT1 receptor independent activation of mineralocorticoid receptor in murine diabetic cardiomyopathy

Background

Diabetes mellitus (DM) has deleterious influence on cardiac performance independent of coronary artery disease and hypertension. The objective of the present study was to investigate the role of the renin-angiotensin-aldosterone system, especially angiotensin II type 1a receptor (AT_1aR) and mineralocorticoid receptor (MR) signaling, in left ventricular (LV) dysfunction induced by diabetes mellitus (DM).

Methods and Results

DM was induced by intraperitoneal injection of streptozotocin (200 mg/kg BW) in wild-type (WT) or AT_1aR knockout (KO) male mice, and they were bred during 6 or 12 weeks. Some KO mice were administered the MR antagonist eplerenone (100 mg/kg body weight). At 6 weeks, LV diastolic function was impaired in WT-DM, but preserved in KO-DM. At that time point MR mRNA expression was upregulated, NADPH oxidase subunit (p47phox) and glutathione peroxidase (GPx1) mRNA expression were upregulated, the staining intensities of LV tissue for 4-hydroxy-2-nonenal was stronger in immunohistochemistry, the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) positive cells was increased, Bcl-2 protein expression was significantly downregulated, and the expression of SERCA2a and phosphorylated phospholamban was depressed in WT-DM, while these changes were not seen in KO-DM. At 12 weeks, however, these changes were also noted in KO-DM. Eplerenone arrested those changes. The plasma aldosterone concentration was elevated in WT-DM but not in KO-DM at 6 weeks. It showed 3.7-fold elevation at 12 weeks even in KO-DM, which suggests “aldosterone breakthrough” phenomenon. However, the aldosterone content in LV tissue was unchanged in KO-DM.

Conclusions

DM induced diastolic dysfunction was observed even in KO at 12 weeks, which was ameliorated by minelarocorticoid receptor antagonist, eplerenone. AT₁-independent MR activation in the LV might be responsible for the pathogenesis of diabetic cardiomyopathy.

A brief history of tumor necrosis factor α--converting enzyme: an overview of ectodomain shedding

Many membrane-bound molecules are cleaved at the cell surface, thereby releasing their extracellular domains. This process, often referred to as ectodomain shedding, has emerged as a critical post-translational mechanism for various membrane-bound ligands, receptors, and adhesion molecules. Tumor necrosis factor α (TNFα)-converting enzyme (TACE/ADAM17) was originally identified as an enzyme responsible for releasing the membrane-bound TNFα precursor. However, subsequent studies found an exceptionally large number of target molecules of TACE, including the ligands for epidermal growth factor receptor, L-selectin, CD44, and vascular growth factor receptor 2. Furthermore, in vivo studies using TACE-conditional knockout mice demonstrated the crucial roles of TACE and ectodomain shedding under both physiological and pathological conditions. However, the potential clinical application of the manipulation of TACE activity remains to be investigated.

Assessment of the number and function of macrophages in the placenta of gestational diabetes mellitus patients

In order to assess the number and function of macrophages in the placenta of pregnancy complicated with gestational diabetes mellitus (GDM) as well as those of normal pregnancies, placenta samples were collected from 15 GDM patients (GDM group) and 10 normal pregnant women (control group). The expression levels of macrophage markers (CD68/CD14) and inflammatory cytokines (IL-6/TNF-α) in placenta were detected using immunohistochemistry and PCR. The results showed that the number of CD68+ or CD14+ cells in the GMD group was remarkably higher than that in the control group (P<0.05), indicating that the number of macrophages in the GDM group was significantly greater than that in the control group. The mRNA expression levels of CD68+, IL-6 and TNF-α were higher in the GMD group than in the control group. In conclusion, more macrophages accumulate in placenta of pregnancy complicated with GDM, and the expression levels of pro-inflammation factors are also increased in GDM pregnancies, suggesting that macrophages and inflammatory mediators (IL-6 and TNF-α) may play an important role in GDM.

Tumor necrosis factor receptor 1 gain-of-function mutation aggravates nonalcoholic fatty liver disease but does not cause insulin resistance in a murine model

Ectodomain shedding of tumor necrosis factor receptor 1 (TNFR1) provides negative feedback to the inflammatory loop induced by TNFα. As the significance of this mechanism in obesity-associated pathologies is unclear, we aimed to unravel how much TNFR1 ectodomain shedding controls the development of nonalcoholic fatty liver disease (NAFLD), as well as its role in the development of insulin resistance. We used knockin mice expressing a mutated TNFR1 ectodomain (p55(Δns)), incapable of shedding and dampen the inflammatory response. Our data show that persistent TNFα signaling through this inability of TNFR1 ectodomain shedding contributes to chronic low-grade inflammation, which is confined to the liver. In spite of this, hepatic lipid levels were not affected by the nonshedding mutation in mice fed a chow diet, nor were they worse off following 12 weeks of high-fat diet (HFD) than controls (p55(+/+)) fed an HFD. We detected inflammatory infiltrates, hepatocellular necrosis, and apoptosis in livers of p55(Δns/Δns) mice fed an HFD, suggesting advanced progression of NAFLD toward nonalcoholic steatohepatitis (NASH). Indeed, fibrosis was present in p55(Δns/Δns) mice, but absent in wildtype mice, confirming that the p55(Δns/Δns) mice had a more severe NASH phenotype. Despite low-grade hepatic inflammation, insulin resistance was not observed in p55(Δns/Δns) mice fed a chow diet, and HFD-induced insulin resistance was no worse in p55(Δns/Δns) mice than p55(+/+) mice.

CONCLUSION

TNFR1 ectodomain shedding is not an essential feedback mechanism in preventing the development of hepatic steatosis or insulin resistance. It is, however, pivotal in attenuating the progression from "simple steatosis" towards a more serious phenotype with many NASH features. Targeting TNFR1 could therefore be beneficial in attenuating NASH.

The role of ADAM17 in metabolic inflammation

The TNF-alpha Converting Enzyme (TACE), also called ADAM17 (A Disintegrin and A Metalloproteinase 17) is a type I transmembrane metalloproteinase involved in the shedding of the extracellular domain of several transmembrane proteins such as cytokines, growth factors, receptors and adhesion molecules. Some of these proteolytic events are part of cleavage cascades known as Regulated Intramembrane Proteolysis and lead to intracellular signaling. Evidence is provided that ADAM17 plays a role in atherosclerosis, in adipose tissue metabolism, insulin resistance and diabetes. The multitude of substrates cleaved by ADAM17 makes this enzyme an attractive candidate to study its role in inflammatory disorders. This review is focused on effects of ADAM17 in major metabolic tissues.

Regulation of TNFα converting enzyme activity in visceral adipose tissue of obese mice

Tumor necrosis factor α (TNFα) is a pro-inflammatory cytokine and one of the major mediators of obesity-induced insulin resistance. TNFα is generated through TNFα converting enzyme (TACE)-mediated cleavage of the transmembrane precursor pro-TNFα. Inhibition of TACE resulted in the improvement in glucose and insulin levels in diabetic animals, suggesting a crucial role of TACE activity in glucose metabolism. However, the regulation of TACE activity in insulin-sensitive tissues has not been fully determined. This study aimed to investigate the impact of TACE in insulin-sensitive tissues in the early stage of the development of obesity. C57BL6 mice were fed standard chow (B6-SC) or high-fat/high-sucrose diet (B6-HF/HS). KK-Ay mice were fed SC ad libitum (Ay-AL) or fed reduced amounts of SC (caloric restriction (CR); Ay-CR). As control for Ay-AL, KK mice fed SC ad libitum (KK-AL) were used. TACE activity in visceral adipose tissue (VAT), but not in liver or skeletal muscle, was significantly elevated in B6-HF/HS and Ay-AL compared with B6-SC and KK-AL, respectively. Phosphorylation of JNK and p38MAPK, but not ERK, in VATs from B6-HF/HS and Ay-AL was also significantly elevated. Ay-CR showed significantly lower TACE, JNK and p38MAPK activities in VAT and serum TNFα level compared with those of Ay-AL. In contrast, intraperitoneal injection of TNFα activated TACE, JNK and p38MAPK activities in VAT in KK mice. In conclusion, during the development of obesity, TACE activity is elevated only in VAT, and CR effectively reduced TACE activity and TACE-mediated pro-TNFα shedding in VAT.

Deficiency of ACE2 in Bone-Marrow-Derived Cells Increases Expression of TNF-α in Adipose Stromal Cells and Augments Glucose Intolerance in Obese C57BL/6 Mice

Deficiency of ACE2 in macrophages has been suggested to promote the development of an inflammatory M1 macrophage phenotype. We evaluated effects of ACE2 deficiency in bone-marrow-derived stem cells on adipose inflammation and glucose tolerance in C57BL/6 mice fed a high fat (HF) diet. ACE2 activity was increased in the stromal vascular fraction (SVF) isolated from visceral, but not subcutaneous adipose tissue of HF-fed mice. Deficiency of ACE2 in bone marrow cells significantly increased mRNA abundance of F4/80 and TNF-α in the SVF isolated from visceral adipose tissue of HF-fed chimeric mice, supporting increased presence of inflammatory macrophages in adipose tissue. Moreover, deficiency of ACE2 in bone marrow cells modestly augmented glucose intolerance in HF-fed chimeric mice and increased blood levels of glycosylated hemoglobin. In summary, ACE2 deficiency in bone marrow cells promotes inflammation in adipose tissue and augments obesity-induced glucose intolerance.