Hepatic STAMP2 alleviates polychlorinated biphenyl-induced steatosis and hepatic iron overload in NAFLD models.

Polychlorinated biphenyls (PCBs) have been associated with neurotoxicity, hepatoxicity, oncogenicity, and endocrine-disrupting effects. Although the recent studies have demonstrated that PCB exposure leads to nonalcoholic fatty liver disease (NAFLD), the underlying mechanism has remained unsolved. In this study, we examined the hepatic effects of a PCB mixture, Aroclor 1260, whose composition mimics human bioaccumulation patterns, and PCB 126 in C57BL/6 mice. Male C57Bl/6 mice were fed a standard diet or a 60% high-fat diet and exposed to Aroclor 1260 (10 mg/kg or 20 mg/kg) or PCB 126 (1 mg/kg or 5 mg/kg) by intraperitoneal injection for a total of four injections (2, 3, 4, and 5 weeks) for 6 weeks. In mice, both Aroclor 1260 and PCB 126-induced liver damage, hepatic steatosis and inflammation. We also observed that PCB exposure-induced hepatic iron overload (HIO). We previously demonstrated that hepatic six transmembrane protein of prostate 2 (STAMP2) may represent a suitable therapeutic target for NAFLD patients. Thus, we further examined whether hepatic STAMP2 is involved in PCB-induced NAFLD. We observed that hepatic STAMP2 was significantly decreased in PCB-induced NAFLD models in vivo and in vitro. Furthermore, overexpression of hepatic STAMP2 using an adenoviral delivery system resulted in improvement of PCB-induced steatosis and HIO in vivo and in vitro. Our findings indicate that enhancing hepatic STAMP2 expression represents a potential therapeutic avenue for the treatment of PCB exposure-induced NAFLD.

Overexpressing STAMP2 attenuates diabetic renal injuries via upregulating autophagy in diabetic rats.

Diabetic nephropathy (DN) is one of the most serious and major renal complications of diabetes. Previously, Six-transmembrane Protein of Prostate 2 (STAMP2) was reported to contribute to nutritional stress. The purpose of this study is to investigate whether overexpression of STAMP2 attenuates diabetic renal injuries in DN rats. We induced the DN rat model by high-fat diet and low-dose streptozotocin and evaluated the metabolite and urine albumin/creatinine. Recombinant adeno-associated virus vectors were injected for overexpression of STAMP2. Pathophysiologic and ultrastructure features of DN by histochemical stain and transmission electron microscope, autophagy-related proteins and signaling pathway by western blotting were assessed. We found the expression of STAMP2 was decreased and autophagy was blunted in DN rat kidneys. Overexpressing STAMP2 significantly ameliorated metabolic disturbance, insulin resistance, and specifically restoring diabetic renal injury. Furthermore, overexpressing STAMP2 improved the autophagy deficiency in DN rats, as revealed by changes in the expressions of Beclin1, p62, and LC3. Furthermore, STAMP2 overexpressing promoted autophagy by inhibiting the mTOR and activating the AMPK/SIRT1 signaling pathway. Our results suggested that STAMP2 overexpression attenuated renal injuries via upregulating autophagy in DN rats. STAMP2 overexpressing promoted autophagy may been involved with inhibition of the mTOR/ULK1 and activation of the AMPK/SIRT1 signaling pathway.

The six-transmembrane protein Stamp2 ameliorates pulmonary vascular remodeling and pulmonary hypertension in mice.

Six-transmembrane protein of prostate (Stamp2) protects from diabetes and atherosclerosis in mice via anti-inflammatory mechanisms. As chronic inflammation is a hallmark of pulmonary arterial hypertension (PAH), we investigated the role of Stamp2. Stamp2 expression was substantially reduced in the lung of humans with idiopathic PAH, as well as in experimental PAH. In Stamp2-deficient mice, hypoxia modestly aggravated pulmonary vascular remodeling and right ventricular pressure compared to WT. As endothelial cell (EC) and pulmonary arterial smooth muscle cell (PASMC) phenotypes drive remodeling in PAH, we explored the role of Stamp2. Knock-down of Stamp2 in human EC neither affected apoptosis, viability, nor release of IL-6. Moreover, Stamp2 deficiency in primary PASMC did not alter mitogenic or migratory properties. As Stamp2 deficiency augmented expression of inflammatory cytokines and numbers of CD68-positive cells in the lung, actions of Stamp2 in macrophages may drive vascular remodeling. Thus, PASMC responses were assessed following treatment with conditioned media of primary Stamp2-/- or WT macrophages. Stamp2-/- supernatants induced PASMC proliferation and migration stronger compared to WT. A cytokine array revealed CXCL12, MCP-1 and IL-6 as most relevant candidates. Experiments with neutralizing antibodies confirmed the role of these cytokines in driving Stamp2's responses. In conclusion, Stamp2 deficiency aggravates pulmonary vascular remodeling via cross-talk between macrophages and PASMC. Despite a substantial pro-inflammatory response, the hemodynamic effect of Stamp2 deficiency is modest suggesting that additional mechanisms apart from inflammation are necessary to induce severe PAH.

Palmitate induces lipoapoptosis in Schwann cells through ROS generation-mediated STAMP2 downregulation.

Free fatty acids (FFAs) are considered the principal inducers of lipotoxicity, leading to cell dysfunction and/or cell death. Lipotoxicity in Schwann cells (SCs) damages neurons, which may be associated with peripheral neuropathies and axon degeneration. However, the molecular mechanism by which FFAs exert lipotoxicity in SCs remains to be established. In the present study, we demonstrate that palmitate exerts lipotoxicity in SCs through apoptosis and that palmitate-induced lipotoxicity in SCs is mediated through reactive oxygen species (ROS) generation. We observed that the six-transmembrane protein of prostate 2 (STAMP2), which plays a pivotal role in lipid homeostasis, is expressed in SCs. We further demonstrate that palmitate induces lipoapoptosis in SCs through ROS generation-mediated STAMP2 downregulation and that STAMP2 depletion accelerates the palmitate-exerted lipoapoptosis in SCs, indicating that STAMP2 confers on SCs the ability to resist palmitate-induced lipotoxicity. In conclusion, palmitate induces lipoapoptosis in SCs through ROS generation-mediated STAMP2 downregulation. Our findings indicate that ROS and STAMP2 may represent suitable targets for pharmacological interventions targeting lipotoxicity-associated peripheral neuropathies and axon degeneration.

Effect of Omega-3 Fatty Acid on STAMP2 Expression in the Heart and Kidney of 5/6 Nephrectomy Rat Model.

Six transmembrane protein of prostate 2 (STAMP2) is a critical modulator of inflammation and metabolism in adipose tissue. There are no data on the expression of STAMP2 in chronic kidney disease, which is an inflammatory disease related to metabolic disorders. This study aimed to investigate STAMP2 expression in the kidney and heart in 5/6 nephrectomy (Nx) rats, and the effect of omega-3 fatty acid (FA) on STAMP2 expression. Male Sprague Dawley rats were divided into three groups: sham control (0.9% saline), 5/6 Nx (0.9% saline), and 5/6 Nx treated with omega-3 FA (300 mg per kg per day by gastric gavage). The expression of STAMP2 in the kidney and heart were examined by western blotting. Serum creatinine levels were higher in 5/6 Nx rats than in controls. Compared with sham controls, the expression of IκB, NF-κB, NOX4, SREBP-1, and LXR were upregulated and STAMP2 and phosphorylated-AMPK expression were downregulated in the kidney and heart of 5/6 Nx rats. Omega-3 FA supplementation prevented these changes in biomarkers related to inflammation and metabolic lipid disorders. Omega 3-FA supplementation induced the upregulation of STAMP2 protein in 5/6 Nx rats, which was associated with an attenuation of inflammation- and metabolic disease-related markers.

Overexpressing STAMP2 attenuates adipose tissue angiogenesis and insulin resistance in diabetic ApoE-/- /LDLR-/- mouse via a PPARγ/CD36 pathway.

The aim of this study was to investigate whether overexpression of STAMP2 improves insulin resistance by regulating angiogenesis in adipose tissues. The characteristics of diabetic mice were measured by serial metabolite and pathology tests. Samples were obtained from epididymal, subcutaneous and brown adipose tissues. Histological and morphological analysis demonstrated that STAMP2 gene overexpression reduced adipocyte size, angiogenesis in epididymal and brown adipose tissues. On aortic ring assay, microvessels sprouting from aortas were significantly inhibited after STAMP2 gene overexpression. The cellular effect of STAMP2 on angiogenesis was explored in human umbilical vein endothelial cells (HUVECs) model. Correlation of STAMP2 and angiogenesis was validated by Ad-STAMP2 transfection and STAMP2 siRNA inhibition. In vitro, overexpression of STAMP2 significantly inhibited endothelial cell migration, tube formation. The effects of Ad-STAMP2 transfection on HUVECs were abolished by treatment with PPARγ antagonist GW9662 (2.5 µM), and the roles of STAMP2 siRNA on HUVECs were also reversed by treatment with PPARγ agonist rosiglitazone (RSG) (0.1 mM). RT-PCR indicated that STAMP2 could regulate levels of adhesion molecules, vascular endothelial growth factor A and CD36. The expression of PPARγ and CD36 was decreased when STAMP2 was inhibited by siRNA, while PPARγ and CD36 were highly expressed after overexpression of STAMP2. Our results suggested that STAMP2 gene overexpression may improve insulin resistance via attenuating angiogenesis in epididymal and brown adipose tissues through the PPARγ/CD36 signalling pathway.

Hepatic STAMP2 alleviates high fat diet-induced hepatic steatosis and insulin resistance.

BACKGROUND & AIMS: Most studies on the role of STAMP2 in metabolism have used adipose tissue. Little knowledge exists concerning the role of STAMP2 in the liver, which is a metabolically central target. We hypothesized that STAMP2 is involved in non-alcoholic fatty liver disease (NAFLD) pathogenesis. METHODS: We examined our hypothesis using human NAFLD patient pathology samples and a high-fat diet (HFD)-induced NAFLD mouse model. The molecular mechanism underlying hepatic STAMP2-mediated lipid imbalance was explored using an oleic acid (OA)-induced NAFLD in vitro model. RESULTS: Noticeably, the expression level of STAMP2 protein was reduced in the livers obtained from NAFLD patients and HFD-induced NAFLD mice. In vivo knockdown of hepatic STAMP2 by siRNA accelerated hepatic steatosis and insulin resistance in mice fed a HFD. Conversely, the delivery of adenoviral STAMP2 (Ad-STAMP2) improved hepatic steatosis in HFD-induced NAFLD mice. The expression of lipogenic or adipogenic factors was increased in both in vitro and in vivo NAFLD models but was reversed by Ad-STAMP2. Adenoviral overexpression of STAMP2 improved insulin resistance in the HFD-induced NAFLD mice. In vivo and in vitro assays demonstrated that STAMP2 modulates insulin sensitivity and glucose metabolism and that STAMP2 counteracts OA-induced insulin resistance by modulating insulin receptor substrate-1 stability. CONCLUSIONS: The present study revealed that hepatic STAMP2 plays a pivotal role in preventing HFD-induced NAFLD and that STAMP2 overexpression improves hepatic steatosis and insulin resistance in NAFLD. Our findings indicate that STAMP2 may represent a suitable target for interventions targeting NAFLD.

Overexpression of STAMP2 suppresses atherosclerosis and stabilizes plaques in diabetic mice.

Our research aims to evaluate the function of the STAMP2 gene, an important trigger in insulin resistance (IR), and explore its role in macrophage apoptosis in diabetic atherosclerotic vulnerable plaques. The characteristics of diabetic mice were measured by serial metabolite and pathology tests. The level of STAMP2 was measured by RT-PCR and Western blot. The plaque area, lipid and collagen content of brachiocephalic artery plaques were measured by histopathological analyses, and the macrophage apoptosis was measured by TUNEL. Correlation of STAMP2/Akt signaling pathway and macrophage apoptosis was validated by Ad-STAMP2 transfection and STAMP2 siRNA inhibition. The diabetic mice showed typical features of IR, hyperglycaemia. Overexpression of STAMP2 ameliorated IR and decreased serum glucose level. In brachiocephalic lesions, lipid content, macrophage quantity and the vulnerability index were significantly decreased by overexpression of STAMP2. Moreover, the numbers of apoptotic cells and macrophages in lesions were both significantly decreased. In vitro, both mRNA and protein expressions of STAMP2 were increased under high glucose treatment. P-Akt was highly expressed and caspase-3 was decreased after overexpression of STAMP2. However, expression of p-Akt protein was decreased and caspase-3 was increased when STAMP2 was inhibited by siRNA. STAMP2 overexpression could exert a protective effect on diabetic atherosclerosis by reducing IR and diminishing macrophage apoptosis.

Analysis of TRIP Steel HCT690 Deformation Behaviour for Prediction of the Deformation Process and Spring-Back of the Material via Numerical Simulation.

This paper deals with the analysis of TRIP steel HCT690 deformation behaviour. The mechanical properties and deformation characteristics of the tested material are determined using selected material tests and tests that consider the required stress states used to define the yield criterion boundary condition and subsequent deformation behaviour in the region of severe plastic deformation. The measured data are subsequently implemented in the numerical simulation of sheet metal forming, where they are used as input data for the computational process in the form of a selected material model defining the yield criterion boundary and, furthermore, the material hardening law during deformation of the material. The chosen numerical simulation process corresponds to the sheet metal forming process, including the subsequent spring-back of the material, when the force does not affect the material. Furthermore, the influence of the chosen computational model and selected process parameters on the deformation and spring-back process of the material is evaluated. In addition to that, at the end of the paper, the results from the numerical simulation are compared with experimentally produced sheet stamping.

Overexpressing six-transmembrane protein of prostate 2 (STAMP2) alleviates sepsis-induced acute lung injury probably by hindering M1 macrophage polarization via the NF-κB pathway.

INTRODUCTION: Acute lung injury (ALI) is a major cause of death in sepsis patients. The Six-transmembrane protein of prostate 2 (STAMP2) is a key regulator of inflammation, while its role in septic ALI remains unclear. MATERIAL AND METHODS: Male C57BL/6 mice were subjected to cecal ligation puncture (CLP) to induce experimental sepsis whereas lipopolysaccharide (LPS)-stimulated RAW 264.7 cells were used as the models of septic ALI in vivo and in vitro, respectively. Overexpression of STAMP2 in mouse lungs and RAW264.7 cells was performed with an adenoviral vector. We measured histological lung injury, lung wet/dry weight (W/D) ratio, and pulmonary myeloperoxidase (MPO) activity to assess lung injury extent. Cell counts in bronchoalveolar lavage fluid (BALF) were measured using Giemsa staining. The concentration of inflammatory factors was detected by enzyme-linked immunosorbent assay. The polarization of macrophages was evaluated by inducible nitric oxide synthase (iNOS) and F4/80 staining. The activation of cell apoptosis and NF-κB pathway was evaluated using Western blot, TUNEL staining, immunofluorescence, and immunohistochemistry. RESULTS: Overexpression of STAMP2 alleviated CLP-induced lung injury of mice with decreased W/D ratio of the lung, and MPO activity in lung tissue. STAMP2 overexpression reduced the lung infiltration of inflammatory cells, and the levels of TNF-a, IL-6, and macrophage chemoattractant protein-1 (MCP-1) in BALF. Overexpressed STAMP2 inhibited macrophage M1 polarization in lung tissues as indicated by F4/80 and iNOS stainings in lung tissue. STAMP2 overexpression inhibited RAW 264.7 cell apoptosis by increasing Bcl-2 and decreasing Bax and cleaved-caspase 3 expression. Besides, STAMP2 overexpression suppressed nuclear factor κB (NF-κB) p65 pathway activation, as evidenced by reduced phosphorylation of IκBα, and phosphorylation and translocation of NF-κB p65. In vitro study further proved that STAMP2 overexpression suppressed the NF-κB pathway (IκBα/p65) in macrophages and decreased macrophage M1 polarization and M1-associated inflammatory factor production (TNF-a, IL-6, and MCP-1). CONCLUSIONS: Our study for the first time demonstrated that STAMP2 might be able to reduce inflammation in sepsis-induced ALI by inhibiting macrophage M1 polarization through repressing NF-κB signaling activation.

Experimental and Numerical Analysis of the Residual Stresses in Seamed Pipe in Dependence on Welding and Metal Forming.

Concerning the increasingly widespread utilization of the finite element method (FEM), the concept of the so-called virtual factory is also gaining ground, and not only in the engineering industry. This approach does not use numerical simulations of individual production technologies separately but treats the entire production process as a chain of interrelated technologies. Thus, the output data from one technology is taken as input data for the following technology. The resulting thermal and mechanical effects are then not only dealt with within one technology but always comprehensively within the production process. In the consideration of the loading and subsequent service lives of manufactured components, values of residual stresses are one of the very important characteristics. For these reasons, this paper deals with the effect of residual stresses' magnitude and distribution during the formation and the final springback of the seamed pipe end section with and without respect to the influence of the preceding welding. The resulting residual stress values from numerical simulations are subsequently compared with the actual values of residual stresses experimentally measured using X-ray diffraction.

Dietary obesity and glycemic excursions cause a parallel increase in STEAP4 and pro-inflammatory gene expression in murine PBMCs.

Background: The balance between pro-atherogenic and anti-atherogenic factors is very crucial in the development of atherosclerotic lesions. Although the expression of the six-transmembrane epithelial antigen of the prostate 4 (STEAP4) in myeloid cells is known to be atheroprotective, there is not a single study reporting on the status of STEAP4 expression in circulating monocytes in the early stages of diet-induced obesity or in events of glycemic excursions. Methods: We induced glycemic spikes twice daily for a 1-week duration to rats fed on regular chow and western diet, and analyzed gene expression changes in the peripheral blood mononuclear cells (PBMCs). We also conducted experiments on RAW 264.7 cells to gain insight into some of our in vivo findings. Results: Diet-induced obesity and glycemic excursions independently caused a significant increase in STEAP4 mRNA expression in PBMCs. This was also accompanied by an induction of a substantial number of pro-inflammatory cytokines, chemokines, and chemokine receptors. However, the combined effect of western diet and hyperglycemic spikes was subtle and non-additive. In the in vitro setting, either glucose spikes, persistent hyperglycemia, or a combination of palmitic acid and insulin resulted in a parallel increase in expression of STEAP4 and pro-inflammatory genes. This was, however, significantly abrogated with 4-octyl itaconate or attenuated by inhibitors of p38MAPK and NF-kB. Conclusions: STEAP4 expression in mononuclear cells is induced by increasing inflammation or oxidative stress. The observed increase in STEAP4 expression in circulating monocytes due to visceral obesity or glycemic excursions is a compensatory response. Supplementary Information: The online version contains supplementary material available at 10.1007/s13340-021-00542-1.

The Role of STAMP2 in Pathogenesis of Chronic Diseases Focusing on Nonalcoholic Fatty Liver Disease: A Review.

Nonalcoholic fatty liver disease (NAFLD) is a major health issue. NAFLD can progress from simple hepatic steatosis to nonalcoholic steatohepatitis (NASH). NASH can progress to cirrhosis or hepatocellular carcinoma. Unfortunately, there is no currently approved pharmacologic therapy for NAFLD patients. The six transmembrane protein of prostate 2 (STAMP2), a metalloreductase involved in iron and copper homeostasis, is well known for its critical role in the coordination of glucose/lipid metabolism and inflammation in metabolic tissues. We previously demonstrated that hepatic STAMP2 could be a suitable therapeutic target for NAFLD. In this review, we discuss the emerging role of STAMP2 in the dysregulation of iron metabolism events leading to NAFLD and suggest therapeutic strategies targeting STAMP2.

STAMP2 Attenuates Cardiac Dysfunction and Insulin Resistance in Diabetic Cardiomyopathy via NMRAL1-Mediated NF-κB Inhibition in Type 2 Diabetic Rats.

Background: Previous studies have reported that six transmembrane protein of prostate 2 (STAMP2) attenuates metabolic inflammation and insulin resistance in diabetes mellitus. However, the role of STAMP2 in the diabetic heart is still unclear. Methods: A diabetic rat cardiomyopathy model was established via intraperitoneal STZ injection. STAMP2 was overexpressed in the treatment group using adeno-associated virus. Rat heart diastolic function was measured using echocardiography and a left ventricular catheter, and cardiac interstitial fibrosis was detected by immunohistochemistry and histological staining. Insulin sensitivity and NF-κB expression were shown by Western blotting. NMRAL1 distribution was illustrated by immunofluorescence. Results: STAMP2 expression in the diabetic rat heart was reduced, and exogenous overexpression of STAMP2 improved glucose tolerance and insulin sensitivity and alleviated diastolic dysfunction and myocardial fibrosis. Furthermore, we found that NF-κB signaling is activated in the diabetic heart and that exogenous overexpression of STAMP2 promotes NMRAL1 translocation from the cytoplasm to the nucleus and inhibits p65 phosphorylation. Conclusion: STAMP2 attenuates cardiac dysfunction and insulin resistance in diabetic cardiomyopathy, likely by promoting NMRAL1 retranslocation and NF-κB signaling inhibition.

STAMP2 suppresses autophagy in prostate cancer cells by modulating the integrated stress response pathway.

Six Transmembrane Protein of Prostate 2 (STAMP2) is critical for prostate cancer (PCa) growth. We previously showed that STAMP2 regulates the expression of stress induced transcription factor ATF4, which is implicated in starvation-induced autophagy. We therefore investigated whether STAMP2 is involved in the regulation of autophagy in PCa cells. Here we show that STAMP2 suppresses autophagy in PCa cells through modulation of the integrated stress response axis. We also find that STAMP2 regulates mitochondrial respiration. These findings suggest that STAMP2 has significant metabolic effects through mitochondrial function and autophagy, both of which support PCa growth.

STAMP2 Expression Mediated by Cytokines Attenuates Their Growth-Limiting Effects in Prostate Cancer Cells.

Inflammatory events and dysregulated cytokine expression are implicated in prostate cancer (PCa), but the underlying molecular mechanisms are poorly understood at present. We have previously identified six transmembrane protein of the prostate 2 (STAMP2, also known as STEAP4) as an androgen-regulated gene, as well as a key regulator of PCa growth and survival. STAMP2 is also regulated by, and participates in, inflammatory signaling in other tissues and pathologies. Here, we show that the proinflammatory cytokines interleukin 6 (IL-6) and Interleukin 1 beta (IL-1ß) significantly increase and strongly synergize in promoting STAMP2 expression in PCa cells. The two cytokines increase androgen-induced STAMP2 expression, but not expression of other known androgen target genes, suggesting a unique interplay of androgens and cytokines in regulating STAMP2 expression. Interestingly, STAMP2 knockdown significantly increased the ability of IL-6 and IL-1ß to inhibit PCa cell growth in vitro. These results suggest that STAMP2 may represent a unique node through which inflammatory events mediate their effects on PCa growth and survival.

Stamp2 Protects From Maladaptive Structural Remodeling and Systolic Dysfunction in Post-Ischemic Hearts by Attenuating Neutrophil Activation.

The six-transmembrane protein of prostate 2 (Stamp2) acts as an anti-inflammatory protein in macrophages by protecting from overt inflammatory signaling and Stamp2 deficiency accelerates atherosclerosis in mice. Herein, we describe an unexpected role of Stamp2 in polymorphonuclear neutrophils (PMN) and characterize Stamp2's protective effects in myocardial ischemic injury. In a murine model of ischemia and reperfusion (I/R), echocardiography and histological analyses revealed a pronounced impairment of cardiac function in hearts of Stamp2-deficient- (Stamp2-/- ) mice as compared to wild-type (WT) animals. This difference was driven by aggravated cardiac fibrosis, as augmented fibroblast-to-myofibroblast transdifferentiation was observed which was mediated by activation of the redox-sensitive p38 mitogen-activated protein kinase (p38 MAPK). Furthermore, we observed increased production of reactive oxygen species (ROS) in Stamp2-/- hearts after I/R, which is the likely cause for p38 MAPK activation. Although myocardial macrophage numbers were not affected by Stamp2 deficiency after I/R, augmented myocardial infiltration by polymorphonuclear neutrophils (PMN) was observed, which coincided with enhanced myeloperoxidase (MPO) plasma levels. Primary PMN isolated from Stamp2-/- animals exhibited a proinflammatory phenotype characterized by enhanced nuclear factor (NF)-κB activity and MPO secretion. To prove the critical role of PMN for the observed phenotype after I/R, antibody-mediated PMN depletion was performed in Stamp2-/- mice which reduced deterioration of LV function and adverse structural remodeling to WT levels. These data indicate a novel role of Stamp2 as an anti-inflammatory regulator of PMN and fibroblast-to-myofibroblast transdifferentiation in myocardial I/R injury.

Hepatic Steatosis Alleviated in Diabetic Mice upon Dietary Exposure to Fibroin via Transgenic Rice: Potential STAMP2 Involvement in Hepatocytes.

Many benefits of silk protein fibroin (SPF) have been suggested in biomedical applications; and notably, significant SPF effects have been observed for metabolic syndromes that are directly linked to insulin resistance, such as type 2 diabetes mellitus (T2DM). Based on our previous findings, we believe that SPF from spiders exhibits outstanding glucose-lowering effects in diabetic BKS.Cg-m+/+Leprdb mice. In order to evaluate the dietary effects of SPF in diabetic animals, we generated several lines of transgenic rice (TR) that expresses SPF, and the feeding of TR-SPF to diabetic animals decreased blood glucose levels, but did not change insulin levels. Western blot analyses of hepatic proteins showed that AMP-activated protein kinase (AMPK) expression and phosphorylation both decreased in TR-SPF-fed groups, compared with controls. This finding suggests that the glucose-lowering effects in this diabetic animal model might be AMPK-independent. In contrast, six-transmembrane protein of prostate 2 (STAMP2) was upregulated after TR-SPF exposure. Together with STAMP2, the Akt protein phosphorylation increased after TR-SPF exposure, which indicates that STAMP2 leads to Akt phosphorylation and thus increases insulin sensitivity in hepatocytes. Importantly, the hepatic steatosis that was seen in the liver of diabetic mice was remarkably alleviated in TR-SPF-fed mice. Hepatocytes that were immunopositive for STAMP2 were overwhelmingly observed in hepatic tissues from TR-SPF-fed mice compared to the control. Taken together, these results suggest that feeding diabetic mice with TR-SPF upregulates STAMP2 expression and increases Akt phosphorylation in hepatic tissues and thus potentially alleviates insulin resistance and hepatic steatosis.

Inflammation and ER stress differentially regulate STAMP2 expression and localization in adipocytes.

BACKGROUND: Chronic ER stress and dysfunction is a hallmark of obesity and a critical contributor to metaflammation, abnormal hormone action and altered substrate metabolism in metabolic tissues, such as liver and adipocytes. Lack of STAMP2 in lean mice induces inflammation and insulin resistance on a regular diet, and it is dysregulated in the adipose tissue of obese mice and humans. We hypothesized that the regulation of STAMP2 is disrupted by ER stress. METHODS: 3T3-L1 and MEF adipocytes were treated with ER stress inducers thapsigargin and tunicamycin, and inflammation inducer TNFα. The treatments effect on STAMP2 expression and enzymatic function was assessed. In addition, 3T3-L1 adipocytes and HEK cells were utilized for Stamp2 promoter activity investigation performed with luciferase and ChIP assays. RESULTS: ER stress significantly reduced both STAMP2 mRNA and protein expression in cultured adipocytes whereas TNFα had the opposite effect. Concomitant with loss of STAMP2 expression during ER stress, intracellular localization of STAMP2 was altered and total iron reductase activity was reduced. Stamp2 promoter analysis by reporter assays and chromatin immunoprecipitation, showed that induction of ER stress disrupts C/EBPα-mediated STAMP2 expression. CONCLUSION: These data suggest a clear link between ER stress and quantitative and functional STAMP2-deficiency.

STAMP2 is required for human adipose-derived stem cell differentiation and adipocyte-facilitated prostate cancer growth in vivo.

Six Transmembrane Protein of Prostate 2 (STAMP2) has been implicated in both prostate cancer (PCa) and metabolic disease. STAMP2 has unique anti-inflammatory and pro-metabolic properties in mouse adipose tissue, but there is limited information on its role in human metabolic tissues. Using human adipose-derived stem cells (ASCs), we report that STAMP2 expression is dramatically upregulated during adipogenesis. shRNA-mediated STAMP2 knockdown in ASCs significantly suppresses adipogenesis and interferes with optimal expression of adipogenic genes and adipocyte metabolic function. Furthermore, ASC-derived adipocyte-mediated stimulation of prostate tumor growth in nude mice is significantly reduced upon STAMP2 knockdown in ASC adipocytes. These results suggest that STAMP2 is crucial for normal ASC conversion into adipocytes and their metabolic function, as well as their ability to facilitate PCa growth in vivo.