Soluble T-cadherin secretion from endothelial cells is regulated via insulin/PI3K/Akt signalling.

AIM AND OBJECTIVE: Our recent report showed that soluble T-cadherin promotes pancreatic beta-cell proliferation. However, how and where the secretion of soluble T-cadherin is regulated remain unclear. METHODS AND RESULTS: Soluble T-cadherin levels significantly increased in leptin receptor-deficient db/db mice with hypoinsulinaemia or in wild-type mice treated with insulin receptor blockade by S961. Similar results were observed in human subjects; Diabetic ketoacidosis patients at the time of hospitalization had increased plasma soluble T-cadherin levels, which decreased after insulin infusion therapy. Patients with recurrent ovarian cancer who were administered a phosphatidylinositol-3 kinase (PI3K)-alpha inhibitor (a new anticancer drug) had increased plasma soluble T-cadherin and plasma C-peptide levels. Endothelial cell-specific T-cadherin knockout mice, but not skeletal muscle- or cardiac muscle-specific T-cadherin knockout mice, showed a 26 % reduction in plasma soluble T-cadherin levels and a significant increase in blood glucose levels in streptozocin-induced diabetes. The secretion of soluble T-cadherin from human endothelial cells was approximately 20 % decreased by insulin and this decrease was canceled by blockade of insulin receptor/Akt signalling, not Erk signalling. CONCLUSION: We conclude that insulin regulates soluble T-cadherin levels and soluble T-cadherin secretion from endothelial cells is positively regulated by insulin/insulin receptor/Akt signalling.

Skeletal Myoblast Cells Enhance the Function of Transplanted Islets in Diabetic Mice.

Islet transplantation (ITx) is an established and safe alternative to pancreas transplantation for type 1 diabetes mellitus (T1DM) patients. However, most ITx recipients lose insulin independence by 3 years after ITx due to early graft loss, such that multiple donors are required to achieve insulin independence. In the present study, we investigated whether skeletal myoblast cells could be beneficial for promoting angiogenesis and maintaining the differentiated phenotypes of islets. In vitro experiments showed that the myoblast cells secreted angiogenesis-related cytokines (vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), and stromal-derived factor-1α (SDF-1α)), contributed to maintenance of differentiated islet phenotypes, and enhanced islet cell insulin secretion capacity. To verify these findings in vivo, we transplanted islets alone or with myoblast cells under the kidney capsule of streptozotocin-induced diabetic mice. Compared with islets alone, the group bearing islets with myoblast cells had a significantly lower average blood glucose level. Histological examination revealed that transplants with islets plus myoblast cells were associated with a significantly larger insulin-positive area and significantly higher number of CD31-positive microvessels compared to islets alone. Furthermore, islets cotransplanted with myoblast cells showed JAK-STAT signaling activation. Our results suggest two possible mechanisms underlying enhancement of islet graft function with myoblast cells cotransplantation: "indirect effects" mediated by angiogenesis and "direct effects" of myoblast cells on islets via the JAK-STAT cascade. Overall, these findings suggest that skeletal myoblast cells enhance the function of transplanted islets, implying clinical potential for a novel ITx procedure involving myoblast cells for patients with diabetes.

Pharmacological HIF-1 activation upregulates extracellular vesicle production synergistically with adiponectin through transcriptional induction and protein stabilization of T-cadherin.

Pharmacological activation of hypoxia-inducible factor 1 (HIF-1), a hypoxia-responsive transcription factor, has attracted increasing attention due to its efficacy not only in renal anemia but also in various disease models. Our study demonstrated that a HIF-1 activator enhanced extracellular vesicle (EV) production from cultured endothelial cells synergistically with adiponectin, an adipocyte-derived factor, through both transcriptional induction and posttranscriptional stabilization of an adiponectin binding partner, T-cadherin. Increased EV levels were observed in wild-type mice but not in T-cadherin null mice after consecutive administration of roxadustat. Adiponectin- and T-cadherin-dependent increased EV production may be involved in the pleiotropic effects of HIF-1 activators.

Correlation between plasma glutamate and adiponectin in patients with type 2 diabetes.

Visceral fat accumulation is a major determinant of type 2 diabetes mellitus and cardiovascular diseases. Recent studies have reported that glutamate is the most elevated amino acid in the plasma amino acid profile in patients with obesity and/or visceral fat accumulation. Here, we show the relationship between plasma glutamate and the clinical features of patients with type 2 diabetes. The study subjects were 62 (28 men and 34 women) Japanese patients with type 2 diabetes. Blood profiles, including glutamate and adiponectin (APN) levels and estimated visceral fat area (eVFA), were measured. We also evaluated the plasma amino acid levels in mice with or without obesity by GC/MS analysis. In patients with type 2 diabetes, plasma glutamate was positively correlated with BMI, eVFA, and fasting insulin but negatively correlated with APN and duration of diabetes. Additionally, multiple regression analysis revealed that plasma glutamate was a significant determinant of APN. The plasma glutamate level was most significantly increased in obese mice compared to control mice, and it was negatively correlated with APN. These results suggest that the level of plasma glutamate could be a strong indicator of adipocyte dysfunction in patients with type 2 diabetes.

HSP47 levels determine the degree of body adiposity.

Adiposity varies among individuals with the influence of diverse physiological, pathological, environmental, hormonal, and genetic factors, but a unified molecular basis remains elusive. Here, we identify HSP47, a collagen-specific chaperone, as a key determinant of body adiposity. HSP47 expression is abundant in adipose tissue; increased with feeding, overeating, and obesity; decreased with fasting, exercise, calorie restriction, bariatric surgery, and cachexia; and correlated with fat mass, BMI, waist, and hip circumferences. Insulin and glucocorticoids, respectively, up- and down-regulate HSP47 expression. In humans, the increase of HSP47 gene expression by its intron or synonymous variants is associated with higher body adiposity traits. In mice, the adipose-specific knockout or pharmacological inhibition of HSP47 leads to lower body adiposity compared to the control. Mechanistically, HSP47 promotes collagen dynamics in the folding, secretion, and interaction with integrin, which activates FAK signaling and preserves PPARγ protein from proteasomal degradation, partly related to MDM2. The study highlights the significance of HSP47 in determining the amount of body fat individually and under various circumstances.

ER stress decreases exosome production through adiponectin/T-cadherin-dependent and -independent pathways.

Exosomes, extracellular vesicles (EVs) produced within cells, mediate both the disposal of intracellular waste and communication with distant cells, and they are involved in a variety of disease processes. Although disease modifications of exosome cargos have been well studied, it has been poorly investigated how disease processes, such as endoplasmic reticulum (ER) stress, affect EV production. We previously reported that adiponectin, an adipocyte-secreted salutary factor, increases systemic exosome levels through T-cadherin-mediated enhancement of exosome biogenesis. In the present study, we demonstrated that adiponectin/T-cadherin-dependent EV production was susceptible to ER stress and that low-dose tunicamycin significantly reduced EV production in the presence, but not in the absence, of adiponectin. Moreover, pharmacological or genetic activation of inositol-requiring enzyme 1α, a central regulator of ER stress, downregulated T-cadherin at the mRNA and protein levels as well as attenuated EV production. In addition, adiponectin/T-cadherin-independent EV production was attenuated under ER stress conditions. Repeated administration of tunicamycin to mice decreased circulating small EVs without decreasing tissue T-cadherin expression. Mechanistically, inositol-requiring enzyme 1α activation by silencing of the X-box binding protein 1 transcription factor upregulated the canonical interferon pathway and decreased EV production. The interferon pathway, when it was activated by polyinosinic-polycytidylic acid, also significantly attenuated EV production. Thus, we concluded that ER stress decreases exosome production through adiponectin/T-cadherin-dependent and -independent pathways.

Cardiovascular significance of adipose-derived adiponectin and liver-derived xanthine oxidoreductase in metabolic syndrome.

Visceral fat-based metabolic syndrome has a strong impact on atherosclerotic cardiovascular disease (CVD), clustering diabetes, dyslipidemia, hypertension, hyperuricemia, and non-alcoholic fatty liver disease (NAFLD). Adiponectin, a protein specifically secreted by adipocytes, circulates abundantly in the human bloodstream, but its concentration decreases under pathological conditions such as visceral fat accumulation. Extensive clinical evidence has demonstrated that hypoadiponectinemia is associated with the development of CVD and chronic organ diseases. Although several binding partners of adiponectin, such as AdipoR1/2, have been identified, how adiponectin exerts its multiple beneficial effects on various organs remains to be fully elucidated. Recent progress in adiponectin research has revealed that adiponectin accumulates on cardiovascular tissues by binding to a unique glycosylphosphatidylinositol-anchored T-cadherin. The adiponectin/T-cadherin complex enhances exosome biogenesis and secretion, which may contribute to the maintenance of cellular homeostasis and tissue regeneration, particularly in the vasculature. Xanthine oxidoreductase (XOR) is a rate-limiting enzyme that catabolizes hypoxanthine and xanthine to uric acid. XOR produces reactive oxygen species in the reaction process, suggesting that XOR is involved in the pathological mechanism underlying CVD progression. Recent findings from clinical and laboratory studies have shown strong positive correlations between plasma XOR activity and liver enzymes. Furthermore, especially in NAFLD conditions, excessive hepatic XOR leaked into the bloodstream accelerates purine catabolism in the circulation, using hypoxanthine secreted from vascular endothelial cells and adipocytes, which can promote vascular remodeling. In this review, we focused on the cardiovascular significance of adipose-derived adiponectin and liver-derived XOR in the development of CVD associated with metabolic syndrome.

Chronic hyperadiponectinemia induced by transgenic overexpression increases plasma exosomes without significantly improving glucose and lipid metabolism.

The fat-derived factor, adiponectin, is considered a salutary circulating factor. We recently demonstrated that native adiponectin binds T-cadherin and promotes intracellular biogenesis and secretion of the exosome. Exosomes play important roles in various aspects of homeostasis, including glucose and energy metabolism. However, it remains unclear whether and how the promotion of exosome production by adiponectin in vivo is beneficial for glucose and lipid metabolism. In the present study, overexpression of human adiponectin in mice resulted in an increased number of circulating exosomes, but it did not significantly improve glucose metabolism, change body weights, or change triglyceride clearance under a high-fat diet. Multiple small doses of streptozotocin increased blood glucose and decreased triglyceride clearance similarly in both wild-type and transgenic mice. Thus, these results indicated that human adiponectin overexpression in mice increases plasma exosomes but does not significantly influence glucose and lipid metabolism.

The Effects of Topiroxostat, a Selective Xanthine Oxidoreductase Inhibitor, on Arterial Stiffness in Hyperuricemic Patients with Liver Dysfunction: A Sub-Analysis of the BEYOND-UA Study.

BACKGROUND: The effects of uric acid (UA)-lowering therapy with xanthine oxidoreductase (XOR) inhibitors on the development of cardiovascular diseases remain controversial. Based on recent findings that plasma XOR activity increased in liver disease conditions, we conducted a sub-analysis of the BEYOND-UA study to examine the differential effects of topiroxostat on arterial stiffness based on liver function in hyperuricemic individuals with hypertension. METHODS: Sixty-three subjects treated with topiroxostat were grouped according to baseline alanine aminotransferase (ALT) levels (above or below cut-off values of 22, 30, or 40 U/L). The primary endpoint was changes in the cardio-ankle vascular index (CAVI) from baseline to 24 weeks. RESULTS: Significant reductions in CAVI during topiroxostat therapy occurred in subjects with baseline ALT ≥30 U/L or ≥40 U/L, and significant between-group differences were detected. Brachial-ankle pulse wave velocity significantly decreased in the ALT-high groups at all cut-off values. Reductions in morning home blood pressure and serum UA were similar regardless of the baseline ALT level. For eleven subjects with available data, ALT-high groups showed high plasma XOR activity, which was significantly suppressed by topiroxostat. CONCLUSIONS: Topiroxostat improved arterial stiffness parameters in hyperuricemic patients with liver dysfunction, which might be related to its inhibitory effect on plasma XOR.

Soluble T-cadherin promotes pancreatic ß-cell proliferation by upregulating Notch signaling.

Endogenous humoral factors that link systemic and/or local insulin demand to pancreatic ß-cells have not been identified. Here, we demonstrated that T-cadherin, a unique glycosylphosphatidylinositol-anchored cadherin primarily expressed in vascular endothelial cells and cardiac and skeletal muscle cells, but not in pancreatic ß-cells, was secreted as soluble forms and was important for ß-cell proliferation. Cdh13 (T-cadherin) knockout mice exhibited impaired glucose handling due to attenuated ß-cell proliferation under high-fat diet conditions. The gene expression analyses indicated the impairment in cell cycle and Notch signaling in the islets of T-cadherin knockout mice under high-fat diet conditions. In streptozotocin-induced diabetes, the replacement of soluble T-cadherin improved ß-cell mass and blood glucose levels in T-cadherin knockout mice. Recombinant soluble T-cadherin upregulated Notch signaling in cultured murine islets. We concluded that soluble T-cadherin could work as an endogenous humoral factor whose signaling pathways including Notch signaling regulate ß-cell proliferation under diabetic conditions in mice.

Extracellular Vesicles as an Endocrine Mechanism Connecting Distant Cells.

The field of extracellular vesicles (EVs) has expanded tremendously over the last decade. The role of cell-to-cell communication in neighboring or distant cells has been increasingly ascribed to EVs generated by various cells. Initially, EVs were thought to a means of cellular debris or disposal system of unwanted cellular materials that provided an alternative to autolysis in lysosomes. Intercellular exchange of information has been considered to be achieved by well-known systems such as hormones, cytokines, and nervous networks. However, most research in this field has searched for and found evidence to support paracrine or endocrine roles of EV, which inevitably leads to a new concept that EVs are synthesized to achieve their paracrine or endocrine purposes. Here, we attempted to verify the endocrine role of EV production and their contents, such as RNAs and bioactive proteins, from the regulation of biogenesis, secretion, and action mechanisms while discussing the current technical limitations. It will also be important to discuss how blood EV concentrations are regulated as if EVs are humoral endocrine machinery.

Favine/CCDC3 deficiency accelerated atherosclerosis and thrombus formation is associated with decreased MEF2C-KLF2 pathway.

Currently, no mouse models manifest calcification and thrombus formation, which is frequently associated with human atherosclerosis. We demonstrated that lack of Favine/CCDC3 in apoE knockout mice accelerated atherosclerosis accompanied by large cholesterol crystals and calcification, and also promoted thrombus formation in the left ventricle and arteries. Circulating Favine was detectable in WT mouse plasma. RNA-sequencing analysis of aortae in DKO mice showed similar gene expression patterns of human atherosclerosis with unstable and vulnerable plaques. Importantly, human FAVINE mRNA expressions were lower in atheroma plaque than in adjacent intact aortic tissue and decreased with the progression of atherosclerosis. Pathway analysis of aortae in DKO mice suggested the decrease of the MEF2C-KLF2-mediated transcriptional pathway. Favine insufficiency and its attenuated downstream pathways may increase atherosclerosis progression with calcification and thrombus, which have not previously been fully modeled in experimental animals. Favine and its downstream pathways may have therapeutic potential for atherosclerosis.

SARS-CoV-2 infection impairs the insulin/IGF signaling pathway in the lung, liver, adipose tissue, and pancreatic cells via IRF1.

BACKGROUND: COVID-19 can cause multiple organ damages as well as metabolic abnormalities such as hyperglycemia, insulin resistance, and new onset of diabetes. The insulin/IGF signaling pathway plays an important role in regulating energy metabolism and cell survival, but little is known about the impact of SARS-CoV-2 infection. The aim of this work was to investigate whether SARS-CoV-2 infection impairs the insulin/IGF signaling pathway in the host cell/tissue, and if so, the potential mechanism and association with COVID-19 pathology. METHODS: To determine the impact of SARS-CoV-2 on insulin/IGF signaling pathway, we utilized transcriptome datasets of SARS-CoV-2 infected cells and tissues from public repositories for a wide range of high-throughput gene expression data: autopsy lungs from COVID-19 patients compared to the control from non-COVID-19 patients; lungs from a human ACE2 transgenic mouse infected with SARS-CoV-2 compared to the control infected with mock; human pluripotent stem cell (hPSC)-derived liver organoids infected with SARS-CoV-2; adipose tissues from a mouse model of COVID-19 overexpressing human ACE2 via adeno-associated virus serotype 9 (AAV9) compared to the control GFP after SARS-CoV-2 infection; iPS-derived human pancreatic cells infected with SARS-CoV-2 compared to the mock control. Gain and loss of IRF1 function models were established in HEK293T and/or Calu3 cells to evaluate the impact on insulin signaling. To understand the mechanistic regulation and relevance with COVID-19 risk factors, such as older age, male sex, obesity, and diabetes, several transcriptomes of human respiratory, metabolic, and endocrine cells and tissue were analyzed. To estimate the association with COVID-19 severity, whole blood transcriptomes of critical patients with COVID-19 compared to those of hospitalized noncritical patients with COVID-19. RESULTS: We found that SARS-CoV-2 infection impaired insulin/IGF signaling pathway genes, such as IRS, PI3K, AKT, mTOR, and MAPK, in the host lung, liver, adipose tissue, and pancreatic cells. The impairments were attributed to interferon regulatory factor 1 (IRF1), and its gene expression was highly relevant to risk factors for severe COVID-19; increased with aging in the lung, specifically in men; augmented by obese and diabetic conditions in liver, adipose tissue, and pancreatic islets. IRF1 activation was significantly associated with the impaired insulin signaling in human cells. IRF1 intron variant rs17622656-A, which was previously reported to be associated with COVID-19 prevalence, increased the IRF1 gene expression in human tissue and was frequently found in American and European population. Critical patients with COVID-19 exhibited higher IRF1 and lower insulin/IGF signaling pathway genes in the whole blood compared to hospitalized noncritical patients. Hormonal interventions, such as dihydrotestosterone and dexamethasone, ameliorated the pathological traits in SARS-CoV-2 infectable cells and tissues. CONCLUSIONS: The present study provides the first scientific evidence that SARS-CoV-2 infection impairs the insulin/IGF signaling pathway in respiratory, metabolic, and endocrine cells and tissues. This feature likely contributes to COVID-19 severity with cell/tissue damage and metabolic abnormalities, which may be exacerbated in older, male, obese, or diabetic patients.

Human adipose-derived mesenchymal stem cells prevent type 1 diabetes induced by immune checkpoint blockade.

AIMS/HYPOTHESIS: Immunomodulators blocking cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) or programmed death-ligand 1 (PD-L1) have improved the treatment of a broad spectrum of cancers. These immune checkpoint inhibitors (ICIs) reactivate the immune system against tumour cells but can also trigger autoimmune side effects, including type 1 diabetes. Mesenchymal stem cell (MSC) therapy is the most prevalent cell therapy, with tissue-regenerating, anti-fibrosis and immunomodulatory functions provided by the secretome of the cells. Here, we examined whether systemic MSC treatment could prevent the development of type 1 diabetes in a NOD mouse model. METHODS: The purified PD-L1 monoclonal antibody was administered to induce diabetes in male NOD mice which normally do not develop diabetes. Human adipose-derived MSCs were administered by tail vein injections. T cells, macrophages and monocyte-derived macrophages expressing C-X-C motif chemokine ligand 9 (CXCL9) in pancreatic sections of NOD mice and a cancer patient who developed diabetes following the ICI treatments were analysed by immunofluorescence. Tissue localisation of the injected MSCs, plasma exosome levels and plasma cytokine profiles were also investigated. RESULTS: PD-1/PD-L1 blockade induced diabetes in 16 of 25 (64%) NOD mice which received anti-PD-L1 mAb without hMSCs [MSC(-)], whereas MSC administration decreased the incidence to four of 21 (19%) NOD mice which received anti-PD-L1 mAb and hMSCs [MSC(+)]. The PD-1/PD-L1 blockade significantly increased the area of CD3-positive T cells (6.2-fold) and macrophage-2 (Mac-2) antigen (2.5-fold)- and CXCL9 (40.3-fold)-positive macrophages in the islets. MSCs significantly reduced T cell (45%) and CXCL9-positive macrophage (67%) accumulation in the islets and the occurrence of diabetes. The insulin content (1.9-fold) and islet beta cell area (2.7-fold) were also improved by MSCs. T cells and CXCL9-positive macrophages infiltrated into the intricate gaps between the beta cells in the islets by PD-1/PD-L1 blockade. Such immune cell infiltration was largely prevented by MSCs. The most striking difference was observed in the CXCL9-positive macrophages, which normally did not reside in the beta cell region in the islets but abundantly accumulated in this area after PD-1/PD-L1 blockade and were prevented by MSCs. The CXCL9-positive macrophages were also observed in the islets of a cancer patient who developed diabetes following the administration of ICIs but few CXCL9-positive macrophages were observed in a control patient. Mechanistically, the injected MSCs accumulated in the lung but not in the pancreas and strongly increased plasma exosome levels and changed plasma cytokine profiles. CONCLUSIONS/INTERPRETATION: Our results suggest that MSCs can prevent the incidence of diabetes associated with immune checkpoint cancer therapy and may be worth further consideration for new adjuvant cell therapy.

Time-Series Change of Serum Soluble T-Cadherin Concentrations and Its Association with Creatine Kinase-MB Levels in ST-Segment Elevation Myocardial Infarction.

AIMS: T-cadherin (T-cad) is a specific binding partner of adiponectin (APN), adipocyte-specific secretory protein. APN exhibits organ protection via the T-cad-dependent accumulation onto several tissues such as the aorta, heart, and muscle. Recently, for the first time, we showed that three forms (130, 100, and 30 kDa) of soluble T-cad existed in human serum and correlated with several clinical parameters in patients with type 2 diabetes. Nevertheless, the significance of soluble T-cad has not been elucidated in the acute stage of cardiovascular diseases. We herein examined soluble T-cad concentrations and investigated their clinical significance in patients with emergency hospital admission due to ST-segment elevation myocardial infarction (STEMI). METHODS: This observational study enrolled 47 patients with STEMI who were treated via primary percutaneous coronary intervention (PCI). Soluble T-cad and APN concentrations were measured by using an enzyme-linked immunosorbent assay. This study is registered with the University Hospital Medical Information Network (Number: UMIN 000014418). RESULTS: Serum concentrations of soluble 130 and 100 kDa T-cad rapidly and significantly decreased after hospitalization and reached the bottom at 72 h after admission (p＜0.001 and p＜0.001, respectively). The patients with high soluble T-cad and low APN concentrations on admission showed a significantly higher area under the curve of serum creatine kinase-MB (p＜0.01). CONCLUSION: Serum soluble T-cad concentration changed dramatically in patients with STEMI, and the high T-cad and low APN concentrations on admission were associated with the myocardial infarction size. Further study is needed to investigate the usefulness of categorizing patients with STEMI by serum T-cad and APN for the prediction of severe prognoses.

Adiponectin accumulation in the retinal vascular endothelium and its possible role in preventing early diabetic microvascular damage.

Adiponectin (APN), a protein abundantly secreted from adipocytes, has been reported to possess beneficial effects on cardiovascular diseases in association with its accumulation on target organs and cells by binding to T-cadherin. However, little is known about the role of APN in the development of diabetic microvascular complications, such as diabetic retinopathy (DR). Here we investigated the impact of APN on the progression of early retinal vascular damage using a streptozotocin (STZ)-induced diabetic mouse model. Our immunofluorescence results clearly showed T-cadherin-dependent localization of APN in the vascular endothelium of retinal arterioles, which was progressively decreased during the course of diabetes. Such reduction of retinal APN accompanied the early features of DR, represented by increased vascular permeability, and was prevented by glucose-lowering therapy with dapagliflozin, a selective sodium-glucose co-transporter 2 inhibitor. In addition, APN deficiency resulted in severe vascular permeability under relatively short-term hyperglycemia, together with a significant increase in vascular cellular adhesion molecule-1 (VCAM-1) and a reduction in claudin-5 in the retinal endothelium. The present study demonstrated a possible protective role of APN against the development of DR.

Possible Involvement of Adipose Tissue in Patients With Older Age, Obesity, and Diabetes With SARS-CoV-2 Infection (COVID-19) via GRP78 (BIP/HSPA5): Significance of Hyperinsulinemia Management in COVID-19.

Aging, obesity, and diabetes are major risk factors for the severe progression and outcome of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (coronavirus disease 2019 [COVID-19]), but the underlying mechanism is not yet fully understood. In this study, we found that the SARS-CoV-2 spike protein physically interacts with cell surface GRP78, which promotes the binding to and accumulation in ACE2-expressing cells. GRP78 was highly expressed in adipose tissue and increased in humans and mice with older age, obesity, and diabetes. The overexpression of GRP78 was attributed to hyperinsulinemia in adipocytes, which was in part mediated by the stress-responsive transcription factor XBP-1s. Management of hyperinsulinemia by pharmacological approaches, including metformin, sodium-glucose cotransporter 2 inhibitor, or ß3-adrenergic receptor agonist, decreased GRP78 gene expression in adipose tissue. Environmental interventions, including exercise, calorie restriction, fasting, or cold exposure, reduced the gene expression of GRP78 in adipose tissue. This study provides scientific evidence for the role of GRP78 as a binding partner of the SARS-CoV-2 spike protein and ACE2, which might be related to the severe progression and outcome of COVID-19 in patients with older age, obesity, and diabetes. The management of hyperinsulinemia and the related GRP78 expression could be a therapeutic or preventative target.

Increased plasma XOR activity induced by NAFLD/NASH and its possible involvement in vascular neointimal proliferation.

Xanthine oxidoreductase (XOR) is an enzyme that catalyzes hypoxanthine to xanthine and xanthine to uric acid, respectively. However, the underlying mechanisms of increased plasma XOR and its pathological roles in systemic diseases, such as atherosclerosis, are not fully understood. In this study, we found that changes in plasma XOR activity after bariatric surgery closely associated with those in liver enzymes, but not with those in BMI. In a mouse model of nonalcoholic fatty liver disease/steatohepatitis (NAFLD/NASH), plasma XOR activity markedly increased. Besides, purine catabolism was accelerated in the plasma per se of NASH mice and human patients with high XOR activity. In our NASH mice, we observed an increased vascular neointima formation consisting of dedifferentiated vascular smooth muscle cells (SMCs), which was significantly attenuated by topiroxostat, a selective XOR inhibitor. In vitro, human liver S9-derived XOR promoted proliferation of SMCs with phenotypic modulation and induced ROS production by catabolizing hypoxanthine released from human endothelial cells. Collectively, the results from human and mouse models suggest that increased plasma XOR activity, mainly explained by excess hepatic leakage, was involved in the pathogenesis of vascular injury, especially in NAFLD/NASH conditions.

Identification and Clinical Associations of 3 Forms of Circulating T-cadherin in Human Serum.

CONTEXT: T-cadherin (T-cad) is a glycosylphosphatidylinositol (GPI)-anchored cadherin that mediates adiponectin to induce exosome biogenesis and secretion, protect cardiovascular tissues, promote muscle regeneration, and stimulate therapeutic heart protection by transplanted mesenchymal stem cells. CDH13, the gene locus of T-cad, affects plasma adiponectin levels most strongly, in addition to affecting cardiovascular disease risk and glucose homeostasis. Recently, it has been suggested that T-cad exists in human serum, although the details are still unclear. OBJECTIVE: To validate the existence of T-cad forms in human serum and investigate the association with clinical parameters of type 2 diabetes patients. METHODS: Using newly developed monoclonal antibodies against T-cad, pooled human serum was analyzed, and novel T-cad enzyme-linked immunosorbent assays (ELISAs) were developed. The serum T-cad concentrations of 183 Japanese type 2 diabetes patients were measured in a cross-sectional observational study. The main outcome measure was the existence of soluble T-cad in human serum. RESULTS: There were 3 forms of soluble T-cad: a 130-kDa form with a prodomain, a 100-kDa mature form, and a 30-kDa prodomain in human serum. Using newly developed ELISAs to measure them simultaneously, we found that the 130-kDa form of T-cad positively correlated with plasma adiponectin (r = 0.28, P < .001), although a physiological interaction with adiponectin was not observed in serum. The unique 30-kDa prodomain was associated with several clinical parameters in diabetes patients. CONCLUSION: We identified 3 novel forms of soluble T-cad. Their importance as disease markers and/or biomarkers of adiponectin function and the possible bioactivity of the respective molecules require further investigation.

Stimulation of exosome biogenesis by adiponectin, a circulating factor secreted from adipocytes.

Adiponectin is an adipocyte-derived circulating factor that protects various organs and tissues. Such a pleiotropic action mechanism has not yet been fully explained. Clinically important multimer adiponectin existing in serum bound to cells expressing T-cadherin, a glycosylphosphatidylinositol-anchored cadherin, but not to the cells expressing other known receptors, AdipoRs or calreticulin. Adiponectin bound to the cell-surface, accumulated inside of multivesicular bodies through T-cadherin, and increased exosome biogenesis and secretion from the cells. Such increased exosome production accompanied the reduction of cellular ceramides in endothelial cells and mouse aorta, and enhanced skeletal muscle regeneration. Significantly lower plasma exosome levels were found in mice genetically deficient in either adiponectin or T-cadherin. Therapeutic effects of mesenchymal stem cells (MSCs) for a pressure overload-induced heart failure in mice required the presence of adiponectin in plasma, T-cadherin expression and exosome biogenesis in MSCs themselves, accompanying an increase of plasma exosomes. Essentially all organs seem to have MSCs and/or their related somatic stem cells expressing T-cadherin. Our recent studies suggested the importance of exosome-stimulation by multimer adiponectin in its well-known pleiotropic organ protections.