Expression Of Insulin-degrading Enzyme Research Articles

Reduced insulin clearance in paediatric metabolic (dysfunction)-associated fatty liver disease and its dual role in beta-cell offload and diabetes risk.

Diminished hepatic insulin clearance (HIC) is observed in obese adults and is presumed to be mediated by fatty liver. However, few reports have examined HIC in Chinese children with metabolic (dysfunction)-associated fatty liver disease (MAFLD). This study aimed to investigate the correlation between HIC, insulin sensitivity and β-cell function in obese Chinese children with MAFLD. In total, 204 obese children (74 MAFLD) aged 4-17 years were enrolled into this study. HIC, insulin sensitivity and β-cell function were calculated using the oral glucose tolerance test (1.75 g/kg body weight). Correlation analyses between the HIC and clinical variables were performed using Pearson's product-moment correlation coefficients. HIC and glucose homeostasis were assessed in a high-fat diet mouse model, and liver samples were collected for molecular analysis. Obese children with MAFLD exhibited significantly lower HIC (AUCC-peptide/insulin ratio, p = 0.0019), higher insulin resistance (homeostatic model assessment of insulin resistance, p = 0.002), and increased compensatory β-cell function (homeostatic model assessment-β, p = 0.046) than obese children without liver involvement. Notably, HIC was negatively correlated with insulin sensitivity (r = -0.5035, p < 0.0001) and β-cell function (r = -0.4576, p < 0.0001). However, pancreatic β-cell dysfunction (p = 0.046) was accompanied by future reduced HIC (p = 0.034) in children with MAFLD in prediabetes. In a high-fat diet mouse model, MAFLD mice showed a 50% reduction in insulin-degrading enzyme expression, consistent with the observed decrease in HIC. A lower HIC may offload pancreatic β-cells at an early stage. However, obese children with MAFLD are at risk of developing diabetes, and preventive efforts should be prioritized.

Hepatic WDR23 proteostasis mediates insulin homeostasis by regulating insulin-degrading enzyme capacity

Maintaining insulin homeostasis is critical for cellular and organismal metabolism. In the liver, insulin is degraded by the activity of the insulin-degrading enzyme (IDE). Here, we establish a hepatic regulatory axis for IDE through WDR23-proteostasis. Wdr23KO mice have increased IDE expression, reduced circulating insulin, and defective insulin responses. Genetically engineered human cell models lacking WDR23 also increase IDE expression and display dysregulated phosphorylation of insulin signaling cascade proteins, IRS-1, AKT2, MAPK, FoxO, and mTOR, similar to cells treated with insulin, which can be mitigated by chemical inhibition of IDE. Mechanistically, the cytoprotective transcription factor NRF2, a direct target of WDR23-Cul4 proteostasis, mediates the enhanced transcriptional expression of IDE when WDR23 is ablated. Moreover, an analysis of human genetic variation in WDR23 across a large naturally aging human cohort in the US Health and Retirement Study reveals a significant association of WDR23 with altered hemoglobin A1C (HbA1c) levels in older adults, supporting the use of WDR23 as a new molecular determinant of metabolic health in humans.

Ginsenoside Rg1 promotes β‑amyloid peptide degradation through inhibition of the ERK/PPARγ phosphorylation pathway in an Alzheimer's disease neuronal model.

β-Amyloid peptide (Aβ) deposition in the brain is an important pathological change in Alzheimer's disease (AD). Insulin-degrading enzyme (IDE), which is regulated transcriptionally by peroxisome proliferator-activated receptor γ (PPARγ), is able to proteolyze Aβ. One of the members of the MAPK family, ERK, is able to mediate the phosphorylation of PPARγ at Ser112, thereby inhibiting its transcriptional activity. Ginsenoside Rg1 is one of the active ingredients in the natural medicine ginseng and has inhibitory effects on Aβ production. The present study was designed to investigate whether ginsenoside Rg1 is able to affect the regulation of PPARγ based on the expression of its target gene, IDE, and whether it is able to promote Aβ degradation via inhibition of the ERK/PPARγ phosphorylation pathway. In the present study, primary cultured rat hippocampal neurons were treated with Aβ1-42, ginsenoside Rg1 and the ERK inhibitor PD98059, and subsequently TUNEL staining was used to detect the level of neuronal apoptosis. ELISA was subsequently employed to detect the intra- and extracellular Aβ1-42 levels, immunofluorescence staining and western blotting were used to detect the translocation of ERK from the cytoplasm to the nucleus, immunofluorescence double staining was used to detect the co-expression of ERK and PPARγ, and finally, western blotting was used to detect the phosphorylation of PPARγ at Ser112 and IDE expression. The results demonstrated that ginsenoside Rg1 or PD98059 were able to inhibit primary cultured hippocampal neuron apoptosis induced by Aβ1-42 treatment, reduce the levels of intra- and extraneuronal Aβ1-42 and inhibit the translocation of ERK from the cytoplasm to the nucleus. Furthermore, administration of ginsenoside Rg1 or PD98059 resulted in attenuated co-expression of ERK and PPARγ, inhibition of phosphorylation of PPARγ at Ser112 mediated by ERK and an increase in IDE expression. In addition, the effects when PD98059 to inhibit ERK followed by treatment with ginsenoside Rg1 were found to be more pronounced than those when using PD98059 alone. In conclusion, ginsenoside Rg1 was demonstrated to exert neuroprotective effects on AD via inhibition of the ERK/PPARγ phosphorylation pathway, which led to an increase in IDE expression, the promotion of Aβ degradation and the decrease of neuronal apoptosis. These results could provide a theoretical basis for the clinical application of ginsenoside Rg1 in AD.

Association between polymorphism rs2421943 of the insulin-degrading enzyme and schizophrenia: Preliminary report.

Insulin-degrading enzyme (IDE) is an important gene in studies of the pathophysiology of type 2 diabetes mellitus (T2DM). Recent studies have suggested a possible link between type 2 diabetes mellitus (T2DM) and the pathophysiology of schizophrenia (SZ). At the same time, significant changes in insulin-degrading enzyme (IDE) gene expression have been found in the brains of people with schizophrenia. These findings highlight the need to further investigate the role of IDE in schizophrenia pathogenesis. We enrolled 733 participants from the Czech Republic, including 383 patients with schizophrenia and 350 healthy controls. Our study focused on the single nucleotide polymorphism (SNP) rs2421943 in the IDE gene, which has previously been associated with the pathogenesis of Alzheimer's disease. The SNP was analyzed using the PCR-RFLP method. The G allele of the rs2421943 polymorphism was found to significantly increase the risk of developing SZ (p < 0.01) when a gender-based analysis showed that both AG and GG genotypes were associated with a more than 1.55 times increased risk of SZ in females (p < 0.03) but not in males. Besides, we identified a potential binding site at the G allele locus for has-miR-7110-5p, providing a potential mechanism for the observed association. Our results confirm the role of the IDE gene in schizophrenia pathogenesis and suggest that future research should investigate the relationship between miRNA and estrogen influence on IDE expression in schizophrenia pathogenesis.

Presence of immunogenic alternatively spliced insulin gene product in human pancreatic delta cells

Aims/hypothesisTranscriptome analyses revealed insulin-gene-derived transcripts in non-beta endocrine islet cells. We studied alternative splicing of human INS mRNA in pancreatic islets.MethodsAlternative splicing of insulin pre-mRNA was determined by PCR analysis performed on human islet RNA and single-cell RNA-seq analysis. Antisera were generated to detect insulin variants in human pancreatic tissue using immunohistochemistry, electron microscopy and single-cell western blot to confirm the expression of insulin variants. Cytotoxic T lymphocyte (CTL) activation was determined by MIP-1β release.ResultsWe identified an alternatively spliced INS product. This variant encodes the complete insulin signal peptide and B chain and an alternative C-terminus that largely overlaps with a previously identified defective ribosomal product of INS. Immunohistochemical analysis revealed that the translation product of this INS-derived splice transcript was detectable in somatostatin-producing delta cells but not in beta cells; this was confirmed by light and electron microscopy. Expression of this alternatively spliced INS product activated preproinsulin-specific CTLs in vitro. The exclusive presence of this alternatively spliced INS product in delta cells may be explained by its clearance from beta cells by insulin-degrading enzyme capturing its insulin B chain fragment and a lack of insulin-degrading enzyme expression in delta cells.Conclusions/interpretationOur data demonstrate that delta cells can express an INS product derived from alternative splicing, containing both the diabetogenic insulin signal peptide and B chain, in their secretory granules. We propose that this alternative INS product may play a role in islet autoimmunity and pathology, as well as endocrine or paracrine function or islet development and endocrine destiny, and transdifferentiation between endocrine cells. INS promoter activity is not confined to beta cells and should be used with care when assigning beta cell identity and selectivity.Data availabilityThe full EM dataset is available via www.nanotomy.org (for review: http://www.nanotomy.org/OA/Tienhoven2021SUB/6126-368/). Single-cell RNA-seq data was made available by Segerstolpe et al [13] and can be found at https://sandberglab.se/pancreas. The RNA and protein sequence of INS-splice was uploaded to GenBank (BankIt2546444 INS-splice OM489474).Graphical abstract

Long-Term High-Fat Diet Decreases Renal Insulin-Degrading Enzyme Expression and Function by Inhibiting the PPARγ Pathway.

Long-term high-fat diet (HFD) causes insulin resistance, which is a primary etiological factor in the development of obesity and type 2 diabetes mellitus. Impaired insulin clearance is not only a consequence but also a cause of insulin resistance. The kidney is a major site of insulin clearance, where the insulin-degrading enzyme (IDE) plays a vital role in the proximal tubule. Thus, the study investigates the role of renal IDE in the regulation of insulin resistance in HFD-induced obese mice. Twenty four-weeks of HFD in C57BL/6 mice causes insulin resistance and impaires insulin clearance, accompanied by a decrease in renal IDE expression and activity. Palmitic acid decreases IDE mRNA and protein expressions in HK-2 cells. RNA-Seq analysis found that the PPAR pathway is involved. 24-weeks of HFD decreases renal PPARγ, but not PPARα or PPARβ/δ mRNA expression. The inhibition of IDE expression by palmitic acid is prevented by the PPARγ agonist rosiglitazone. The amount of PPARγ bound to the promoters of IDE is decreased in palmitic acid-treated cells. Rosiglitazone improves insulin clearance and insulin resistance and increases renal IDE expression in HFD fed-mice. Long-term HFD decreases renal IDE expression and activity, and causes insulin resistance, which involves PPARγ.

Experimental approaches for altering the expression of Abeta-degrading enzymes.

Cerebral clearance of amyloid β-protein (Aβ) is decreased in early-onset and late-onset Alzheimer's disease (AD). Aβ is cleared from the brain by enzymatic degradation and by transport out of the brain. More than 20 Aβ-degrading enzymes have been described. Increasing the degradation of Aβ offers an opportunity to decrease brain Aβ levels in AD patients. This review discusses the direct and indirect approaches which have been used in experimental systems to alter the expression and/or activity of Aβ-degrading enzymes. Also discussed are the enzymes' regulatory mechanisms, the conformations of Aβ they degrade, where in the scheme of Aβ production, extracellular release, cellular uptake, and intracellular degradation they exert their activities, and changes in their expression and/or activity in AD and its animal models. Most of the experimental approaches require further confirmation. Based upon each enzyme's effects on Aβ (some of the enzymes also possess β-secretase activity and may therefore promote Aβ production), its direction of change in AD and/or its animal models, and the Aβ conformation(s) it degrades, investigating the effects of increasing the expression of neprilysin in AD patients would be of particular interest. Increasing the expression of insulin-degrading enzyme, endothelin-converting enzyme-1, endothelin-converting enzyme-2, tissue plasminogen activator, angiotensin-converting enzyme, and presequence peptidase would also be of interest. Increasing matrix metalloproteinase-2, matrix metalloproteinase-9, cathepsin-B, and cathepsin-D expression would be problematic because of possible damage by the metalloproteinases to the blood brain barrier and the cathepsins' β-secretase activity. Many interventions which increase the enzymatic degradation of Aβ have been shown to decrease AD-type pathology in experimental models. If a safe approach can be found to increase the expression or activity of selected Aβ-degrading enzymes in human subjects, then the possibility that this approach could slow the AD progression should be examined in clinical trials.

Effects of Insulin-degrading enzyme on the proliferation of swine Sertoli cells.

Sertoli cells, the only somatic cells in testis seminiferous tubules, provide a supporting microenvironment for male germ cells and play essential roles in spermatogenesis. The insulin-degrading enzyme (IDE), a ubiquitous zinc peptidase of the inverzincin family, plays crucial role in sperm production, as IDE-knockout mice presented decreased testis weight and impaired sperm viability and morphology. However, whether and how IDE affects swine Sertoli cell proliferation remains unclear. Thus, in the present study, we aimed to evaluate the effects of IDE on the proliferation of swine Sertoli cells, as well as its underlying molecular mechanism. After knocking down IDE expression with small interfering RNA transfection, we analyzed the proliferation of swine Sertoli cells as well as the expression of related regulatory factors (WT1, ERK, and AKT). The results showed that IDE knockdown promoted swine Sertoli cell proliferation and increased WT1 expression, possibly through activating ERK and AKT. Overall, our findings suggest that IDE may be involved in male reproduction by regulating Sertoli cell proliferation, which provides new information to better understand the regulatory mechanisms of swine Sertoli cells and improve the reproductive traits of male pigs.

Sleeve Gastrectomy-Induced Weight Loss Increases Insulin Clearance in Obese Mice.

Sleeve gastrectomy (SG) successfully recovers metabolic homeostasis in obese humans and rodents while also resulting in the normalization of insulin sensitivity and insulinemia. Reduced insulin levels have been attributed to lower insulin secretion and increased insulin clearance in individuals submitted to SG. Insulin degradation mainly occurs in the liver in a process controlled, at least in part, by the insulin-degrading enzyme (IDE). However, research has yet to explore whether liver IDE expression or activity is altered after SG surgery. In this study, C57BL/6 mice were fed a chow (CTL) or high-fat diet (HFD) for 10 weeks. Afterward, the HFD mice were randomly assigned to two groups: sham-surgical (HFD-SHAM) and SG-surgical (HFD-SG). Here, we confirmed that SG improves glucose-insulin homeostasis in obese mice. Additionally, SG reduced insulinemia by reducing insulin secretion, assessed by the analysis of plasmatic C-peptide content, and increasing insulin clearance, which was evaluated through the calculation of the plasmatic C-peptide:insulin ratio. Although no changes in hepatic IDE activity were observed, IDE expression was higher in the liver of HFD-SG compared with HFD-SHAM mice. These results indicate that SG may be helpful to counteract obesity-induced hyperinsulinemia by increasing insulin clearance, likely through enhanced liver IDE expression.

Sirt3 deficiency induced down regulation of insulin degrading enzyme in comorbid Alzheimer’s disease with metabolic syndrome

SIRT3 deacetylates mitochondrial proteins, thereby enhancing their function. We have previously demonstrated that Sirt3 gene deletion leads to brain mitochondrial dysfunction and neuroinflammation. We also reported that silencing of Sirt3 gene in APP/PS1 mice results in exacerbation of insulin resistance, neuroinflammation and β amyloid plaque deposition. To further understand how metabolic syndrome and amyloid pathology interact, we performed RNA-seq analysis of the brain samples of APP/PS1/Sirt3-/- mice. Gene expression patterns were modulated in metabolic and inflammatory pathways by Sirt3 gene deletion, amyloid pathology, and the combination. Following Sirt3 gene deletion, a key finding was the decreased expression of insulin-degrading enzyme (IDE), an enzyme that regulates the levels of insulin and Aβ peptides. Western diet feeding of Sirt3-/- and APP/PS1 mice resulted in decrease of IDE protein, parallel to Sirt3 downregulation. Conversely, activation of SIRT3 by nicotinamide riboside in vivo and in vitro resulted in IDE upregulation. SIRT3 activation in vivo also increased the levels of neprilysin, another Aβ degrading enzyme and decreased the levels of BACE1 which generates Aβ peptide suggesting SIRT3’s role in amyloid plaque reduction. Our findings provide a plausible mechanism linking metabolic syndrome and amyloid pathology. SIRT3 may be a potential therapeutic target to treat AD.

Altered Surface Expression of Insulin-Degrading Enzyme on Monocytes and Lymphocytes from COVID-19 Patients Both at Diagnosis and after Hospital Discharge.

Although the COVID-19 disease has developed into a worldwide pandemic, its pathophysiology remains to be fully understood. Insulin-degrading enzyme (IDE), a zinc-metalloprotease with a high affinity for insulin, has been found in the interactomes of multiple SARS-CoV-2 proteins. However, the relevance of IDE in the innate and adaptative immune responses elicited by circulating peripheral blood mononuclear cells is unknown. Here, we show that IDE is highly expressed on the surface of circulating monocytes, T-cells (both CD4+ and CD4−), and, to a lower extent, in B-cells from healthy controls. Notably, IDE’s surface expression was upregulated on monocytes from COVID-19 patients at diagnosis, and it was increased in more severe patients. However, IDE’s surface expression was downregulated (relative to healthy controls) 3 months after hospital discharge in all the studied immune subsets, with this effect being more pronounced in males than in females, and thus it was sex-dependent. Additionally, IDE levels in monocytes, CD4+ T-cells, and CD4− T-cells were inversely correlated with circulating insulin levels in COVID-19 patients (both at diagnosis and after hospital discharge). Of note, high glucose and insulin levels downregulated IDE surface expression by ~30% in the monocytes isolated from healthy donors, without affecting its expression in CD4+ T-cells and CD4− T-cells. In conclusion, our studies reveal the sex- and metabolism-dependent regulation of IDE in monocytes, suggesting that its regulation might be important for the recruitment of immune cells to the site of infection, as well as for glucometabolic control, in COVID-19 patients.

New Insights on the Regulation of the Insulin-Degrading Enzyme: Role of microRNAs and RBPs.

The evident implication of the insulin-degrading enzyme (IDE) in Alzheimer’s disease (AD) and type 2 diabetes mellitus (T2DM), among its capacity to degrade insulin and amyloid-β peptide (Aβ), suggests that IDE could be an essential link in the relation between hyperinsulinemia, insulin resistance and AD. However, little is known about the cellular and molecular regulation of IDE expression, and even less has been explored regarding the post-transcriptional regulation of IDE, although it represents a great molecular target of interest for therapeutic treatments. We recently described that miR-7, a novel candidate for linking AD and T2DM at the molecular level, regulates IDE and other key genes in both pathologies, including some key genes involved in the insulin signaling pathway. Here, we explored whether other miRNAs as well as other post-transcriptional regulators, such as RNA binding proteins (RBP), could potentially participate in the regulation of IDE expression in vitro. Our data showed that in addition to miR-7, miR-125, miR-490 and miR-199 regulate IDE expression at the post-transcriptional level. Moreover, we also found that IDE contains multiple potential binding sites for several RBPs, and a narrow-down prediction analysis led us to speculate on a novel regulation of IDE by RALY and HuD. Taken together, these results demonstrate the novel players controlling IDE expression that could represent potential therapeutical targets to treat several metabolic diseases with a high impact on human health, including AD and T2DM.

Effect of moxibustion with deqi on Aβ-receptor mediated transport and enzymatic degradation in hippocampus in rats with Alzheimer's disease

To observe the clinical effect of moxibustion with deqi on Alzheimer's disease (AD) rats, and evaluate its effect on β-amyloid (Aβ) transport and enzymatic degradation proteins, to explore its molecular mechanism for improving cognitive function. Sixty SPF-grade male SD rats were randomly divided into a blank group (8 rats), a sham-operation group (8 rats) and a model establishment group (44 rats). The rats in the model establishment group were injected with Aβ1-42 at bilateral ventricles to establish AD model. Among the 38 rats with successful model establishment, 8 rats were randomly selected as the model group, and the remaining rats were treated with mild moxibustion at "Dazhui" (GV 14), once a day, 40 min each time, for 28 days. According to whether deqi appeared and the occurrence time of deqi, the rats were divided into a deqi group (12 rats), a delayed deqi group (10 rats) and a non-deqi group (8 rats). After the intervention, the Morris water maze test was applied to evaluate the cognitive function; the HE staining was applied to observe the brain morphology; the Western blot method was applied to measure the protein expression of Aβ and its receptor mediated transport [low-density lipoprotein receptor-related protein (LRP) 1, receptor for advanced glycation end products (RAGE), apolipoprotein E (ApoE)] and enzymatic degradation [neprilysin (NEP), insulin degrading enzyme (IDE), endothelin converting enzyme (ECE)-1 and angiotensin converting enzyme (ACE) 2]. Compared with the sham-operation group, in the model group, the escape latency was prolonged (P<0.01), and the times of platform crossing and the ratio of platform quadrant to total time were reduced (P<0.01); the brain tissue was seriously damaged; the expression of hippocampal Aβ and RAGE was increased (P<0.01), and the expression of hippocampal LRP1, ApoE, NEP, IDE, ECE-1 and ACE2 was decreased (P<0.01). Compared with the model group, the escape latency was shortened in the deqi group (P<0.05, P<0.01), and the escape latency in the delayed deqi group and the non-deqi group was shortened from Day 2 to Day 5 (P<0.05, P<0.01), and the times of platform crossing and the ratio of platform quadrant to total time were increased in the deqi group and the delayed deqi group (P<0.01, P<0.05); the brain damage in each moxibustion group was reduced, which was smallest in the deqi group, followed by the delayed deqi group and the non-deqi group; the expression of Aβ and RAGE was decreased (P<0.01, P<0.05) and the expression of LRP1 and IDE was increased in each moxibustion group (P<0.01, P<0.05); the expression of ApoE was increased in the deqi group and the delayed deqi group (P<0.01, P<0.05); the expression of NEP was increased in deqi group (P<0.05), and the expression of ECE-1 and ACE2 was increased in the deqi group and the delayed deqi group (P<0.05). Compared with the delayed deqi group and the non-deqi group, the escape latency in the deqi group was shortened from Day 3 to Day 5 (P<0.05), and the times of platform crossing and the ratio of platform quadrant to total time were increased (P<0.05, P<0.01). Compared with the non-deqi group, the expression of Aβ was reduced (P<0.05), the expression of LRP1 and ApoE was increased in the deqi group (P<0.05). The expression of NEP in the deqi group was higher than that in the delayed deqi group and the non-deqi group (P<0.05). Compared with non-deqi, moxibustion with deqi could promote Aβ transport and degradation, thereby reducing Aβ level in the brain and improving cognitive function for AD rats.

Effects of Red Rice Bran Extract on High-Fat Diet-Induced Obesity and Insulin Resistance in Mice.

Insulin resistance is a salient player in the pathogenesis of obesity and its related abnormal glucose-insulin homeostasis. Red rice bran extract (RRBE) demonstrates several bioactive phytochemicals with anti-diabetic properties. However, little is known about its molecular mechanisms. Therefore, the present study was designed to investigate the anti-insulin resistant mechanisms of RRBE in a model of high-fat diet (HFD)-induced insulin resistance. In this study, mice were randomly divided into four groups: low-fat diet with distilled water (Group L), HFD with distilled water (Group H), HFD with 0.5 g/kg RRBE, and HFD with 1 g/kg RRBE. Metabolic parameters, histological changes in the pancreas, and gene expression levels were evaluated after treating HFD-fed mice with RRBE for six weeks. Mice from Group H exhib-ited significantly higher blood glucose levels prior to and after an oral glucose tolerance test, fasting serum insulin levels, islet size, pancreatic insulin expression levels, and lower skeletal muscle insulin-degrading enzyme (IDE) expression levels compared to Group L. In contrast, these were all significantly restored in the RRBE-treated groups. Also, RRBE treatment was found to upregulate the expression of insulin receptor substrate (IRS) and glucose transporter (GLUT) genes in the adipose tissues and GLUT genes in the muscles and livers of HFD-fed mice. According to our results, RRBE may ameliorate abnormal glucose-insulin metabolism by modulating the expression of insulin, IDE, IRS, and GLUT genes in the major metabolic target tissues of mice after being fed with HFD.

Possible Role of Insulin-Degrading Enzyme in the Physiopathology of Retinitis Pigmentosa.

Insulin-degrading enzyme (IDE) was named after its role as a proteolytic enzyme of insulin. However, recent findings suggest that IDE is a widely expressed, multitask protein, with both proteolytic and non-proteolytic functions. Here, we characterize the expression of IDE in the mammalian retina in both physiological and pathological conditions. We found that IDE was enriched in cone inner segments. IDE levels were downregulated in the dystrophic retina of several mouse models of retinitis pigmentosa carrying distinct mutations. In rd10 mice, a commonly studied mouse model of retinitis pigmentosa, treatment with an IDE activator (a synthetic peptide analog of preimplantation factor) delayed loss of visual function and preserved photoreceptor cells. Together, these results point to potential novel roles for IDE in retinal physiology and disease, further extending the list of diverse functions attributed to this enzyme.

Effects of some anti-diabetic herbal extracts on the insulin-degrading enzyme in human colon cancer Caco-2 cell line.

Objective:Type 2 diabetes mellitus (T2DM) is a condition characterized by insufficient insulin production or insulin resistance. The insulin-degrading enzyme (IDE) is responsible for degrading insulin and is a potential drug target for T2DM treatment. Numerous activities have been proposed for plant extracts, but research on the effects of plant extracts on IDE expression and activity is riddled with drawbacks.Materials and Methods:We investigated the effect of Phaseolus vulgaris, Allium cepa, Portulaca oleracea, Cinnamomum verum, and Citrullus colocynthis extracts on the expression and activity of IDE in the Caco-2 cell line.Results: Findings of RT-PCR showed that IDE gene expression was reduced following treatment with P. vulgaris, C. colocynthis, and C. verum extracts. The results of IDE activity with fluorogenic peptide substrate V also indicated that P. vulgaris, C. colocynthis, and P. oleracea extracts reduced IDE activity in a significant and dose-dependent manner.Conclusion:The hydroalcoholic extracts studied, except for A. cepa, can prevent insulin degradation by reducing the expression and activity of the IDE enzyme. This new insight into the effects of herbal medicines on IDE activity can help future studies.

Medium-Chain Length Fatty Acids Enhance Aβ Degradation by Affecting Insulin-Degrading Enzyme.

The accumulation of amyloid β-protein (Aβ) is one of the major pathological hallmarks of Alzheimer’s disease. Insulin-degrading enzyme (IDE), a zinc-metalloprotease, is a key enzyme involved in Aβ degradation, which, in addition to Aβ production, is critical for Aβ homeostasis. Here, we demonstrate that saturated medium-chain fatty acids (MCFAs) increase total Aβ degradation whereas longer saturated fatty acids result in an inhibition of its degradation, an effect which could not be detected in IDE knock-down cells. Further analysis of the underlying molecular mechanism revealed that MCFAs result in an increased exosomal IDE secretion, leading to an elevated extracellular and a decreased intracellular IDE level whereas gene expression of IDE was unaffected in dependence of the chain length. Additionally, MCFAs directly elevated the enzyme activity of recombinant IDE, while longer-chain length fatty acids resulted in an inhibited IDE activity. The effect of MCFAs on IDE activity could be confirmed in mice fed with a MCFA-enriched diet, revealing an increased IDE activity in serum. Our data underline that not only polyunsaturated fatty acids such as docosahexaenoic acid (DHA), but also short-chain fatty acids, highly enriched, for example in coconut oil, might be beneficial in preventing or treating Alzheimer’s disease.

IL-6 induced enhanced clearance of proANP and ANP by insulin-degrading enzyme in T1DM mice.

Cardiovascular disease (CVD) is a prevalent cause of morbidity and mortality in type I diabetes mellitus (T1DM). However, the pathophysiological mechanisms underlying the relationship between CVD, CVD risk factors, and T1DM have not yet been sufficiently explored. Here, we report that insulin-degrading enzyme (IDE) effectively degrades the precursor of atrial natriuretic peptide (proANP) in HEK293T cells. The pro-inflammatory cytokine IL-6 elicited a significant dose-dependent increase in IDE protein expression. Inhibition of the ERK/MAPK signaling pathway with selumetinib abolished the IL-6-stimulated increase in IDE protein levels and decreased ANP secretion in H9C2 cells. Importantly, the T1DM mouse model displayed lower proANP in the heart and ANP in serum, due to increased IDE expression and activity. Our results suggest a novel role of IL-6 in ANP metabolism via IDE and provide possibilities for new potential therapeutic strategies for diabetes-related cardiovascular complications.

Insulin-Degrading Enzyme Regulates the Proliferation and Apoptosis of Porcine Skeletal Muscle Stem Cells via Myostatin/MYOD Pathway.

Identifying the genes relevant for muscle development is pivotal to improve meat production and quality in pigs. Insulin-degrading enzyme (IDE), a thiol zinc-metalloendopeptidase, has been known to regulate the myogenic process of mouse and rat myoblast cell lines, while its myogenic role in pigs remained elusive. Therefore, the current study aimed to identify the effects of IDE on the proliferation and apoptosis of porcine skeletal muscle stem cells (PSMSCs) and underlying molecular mechanism. We found that IDE was widely expressed in porcine tissues, including kidney, lung, spleen, liver, heart, and skeletal muscle. Then, to explore the effects of IDE on the proliferation and apoptosis of PSMSCs, we subjected the cells to siRNA-mediated knockdown of IDE expression, which resulted in promoted cell proliferation and reduced apoptosis. As one of key transcription factors in myogenesis, MYOD, its expression was also decreased with IDE knockdown. To further elucidate the underlying molecular mechanism, RNA sequencing was performed. Among transcripts perturbed by the IDE knockdown after, a downregulated gene myostatin (MSTN) which is known as a negative regulator for muscle growth attracted our interest. Indeed, MSTN knockdown led to similar results as those of the IDE knockdown, with upregulation of cell cycle-related genes, downregulation of MYOD as well as apoptosis-related genes, and enhanced cell proliferation. Taken together, our findings suggest that IDE regulates the proliferation and apoptosis of PSMSCs via MSTN/MYOD pathway. Thus, we recruit IDE to the gene family of regulators for porcine skeletal muscle development and propose IDE as an example of gene to prioritize in order to improve pork production.

Comparative analysis of electroacupuncture, metformin and their combination on cognitive function and senile plaques of cerebral cortex and hippocampus in APP/PS1 mice

To compare the effect of electroacupuncture (EA), metformin and EA plus metformin on the cognitive ability and senile plaques (SPs) in cerebral cortex and hippocampus of Alzheimer's disease (AD) mice, so as to explore a better treatment method for AD. Twenty-four male APP/PS1 mice were randomly divided into model, metformin (medication), EA and EA+medication groups, with 6 mice in each group. Other 6 male wild C57 mice were used as the control group. EA (2 Hz, 1.0 mA) was applied to "Baihui" (GV20) and "Shenshu" (BL23) for 15 min, once a day, for 4 weeks, with 1 day's off every week. The mice of the medication group received gavage of metformin (300 mg·kg-1·d-1) once a day for 4 weeks. Morris water maze tests were used to assess the cognitive function of mice. H.E. staining was used to observe the histopathological changes of neurons in the cortex and hippocampus. Immunohistochemical method was used to observe the cerebral cortex and hippocampal SPs. The expression levels of SPs formation-related proteins: β-site amyloid precursor protein cleaving enzyme 1(βACE1) and insulin-degrading enzyme (IDE) in the cortex and hippocampus were detected by Western blot. Compared with the control group, the escape latency, number of SPs and the expression of βACE1 in the cortex and hippocampus were ob-viously increased (P<0.01), and the times of platform quadrant crossing and the expression of IDE protein were markedly decreased in the model group (P<0.01). In comparison with the model group, the escape latency, and the number of SPs and expression of βACE1 proteins in the cortex and hippocampus in the 3 treatment groups were significantly down-regulated (P<0.01), while the times of platform quadrant crossing, and the expression of IDE protein in both cortex and hippocampus of the three treatment groups were considerably up-regulated (P<0.01). Comparison among the three treatment groups showed that the therapeutic effect of EA+medication was significantly superior to that of medication and simple EA in down-regulating the escape latency, the number of SPs and expression of βACE1 in the cortex and hippocampus (P<0.01), and in up-regulating the times of the platform quadrant crossing, and expression of IDE protein in both cortex and hippocampus (P<0.01). No significant differences were found between the simple medication and simple EA in all the indexes mentioned above (P>0.05). EA, metformin and EA plus metformin can improve cognitive ability and relieve SP formation in cerebral cortex and hippocampus in AD mice, which may be associated with their functions in down-regulating the expression of βACE1 and up-regulating the expression of IDE. The therapeutic effects of EA plus metformin are apparently better than those of simple EA and simple metformin.