Down-regulation Of Insulin Receptors Research Articles

Gingipain from Porphyromonas gingivalis causes insulin resistance by degrading insulin receptors through direct proteolytic effects

Periodontitis is a critical risk factor for the occurrence and development of diabetes. Porphyromonas gingivalis may participate in insulin resistance (IR) caused by periodontal inflammation, but the functional role and specific mechanisms of P. gingivalis in IR remain unclear. In the present study, clinical samples were analysed to determine the statistical correlation between P. gingivalis and IR occurrence. Through culturing of hepatocytes, myocytes, and adipocytes, and feeding mice P. gingivalis orally, the functional correlation between P. gingivalis and IR occurrence was further studied both in vitro and in vivo. Clinical data suggested that the amount of P. gingivalis isolated was correlated with the Homeostatic Model Assessment for IR score. In vitro studies suggested that coculture with P. gingivalis decreased glucose uptake and insulin receptor (INSR) protein expression in hepatocytes, myocytes, and adipocytes. Mice fed P. gingivalis tended to undergo IR. P. gingivalis was detectable in the liver, skeletal muscle, and adipose tissue of experimental mice. The distribution sites of gingipain coincided with the downregulation of INSR. Gingipain proteolysed the functional insulin-binding region of INSR. Coculture with P. gingivalis significantly decreased the INSR–insulin binding ability. Knocking out gingipain from P. gingivalis alleviated the negative effects of P. gingivalis on IR in vivo. Taken together, these findings indicate that distantly migrated P. gingivalis may directly proteolytically degrade INSR through gingipain, thereby leading to IR. The results provide a new strategy for preventing diabetes by targeting periodontal pathogens and provide new ideas for exploring novel mechanisms by which periodontal inflammation affects the systemic metabolic state.

Regulation of Insulin Clearance by Non-Esterified Fatty Acids

Insulin stores lipid in adipocytes and prevents lipolysis and the release of non-esterified fatty acids (NEFA). Excessive release of NEFA during sustained energy supply and increase in abdominal adiposity trigger systemic insulin resistance, including in the liver, a major site of insulin clearance. This causes a reduction in insulin clearance as a compensatory mechanism to insulin resistance in obesity. On the other hand, reduced insulin clearance in the liver can cause chronic hyperinsulinemia, followed by downregulation of insulin receptor and insulin resistance. Delineating the cause–effect relationship between reduced insulin clearance and insulin resistance has been complicated by the fact that insulin action and clearance are mechanistically linked to insulin binding to its receptors. This review discusses how NEFA mobilization contributes to the reciprocal relationship between insulin resistance and reduced hepatic insulin clearance, and how this may be implicated in the pathogenesis of non-alcoholic fatty liver disease.

1320-P: Insulin Receptors and Their Signal Transduction Pathways in Choroid Plexus

The insulin receptor (IR) is a tyrosine kinase receptor present in cell membranes. It is highly expressed in hepatocytes (where it promotes glycogenesis and inhibits gluconeogenesis) , and skeletal muscle and fat (where it facilitates glucose uptake by translocation of the glucose transporter GLUT4) . IR expression is also found throughout the brain, both in neurons and all glial cell types, and for decades impaired insulin signaling has been implicated in the onset and development of Alzheimer’s disease. IR expression pattern in the brain parenchyma is heterogeneous, with highest levels of expression found in olfactory bulb, hypothalamus, and hippocampus. However, the choroid plexus (CP) , a structure present in all 4 ventricles of the brain and responsible for the secretion of cerebrospinal fluid, has the highest affinity for insulin binding compared to any other brain region. This work aims to characterize the insulin signaling in the epithelial cells of the choroid plexus (EChP) and its possible implications in diseases of the brain. Relative expression levels of specific splicing variants of the Insr gene in dissected CP of adult mice were evaluated by qPCR and revealed predominant expression of the variant coding for isoform IR-A when compared to isoform IR-B. In vitro stimulation of EChP with insulin elicits a classical tyrosine kinase cascade, with activation of both the mitogenic (ERK) and metabolic (Akt) arms of the insulin signaling pathway, in a time-and concentration-dependent manner. Using pharmacological (S961, an insulin receptor antagonist) and genetic (insulin receptor shRNA, and Insr cre-loxP) approaches, we show that downregulation of IR in these cells not only impairs insulin signaling, but it also decreases IGF2’s ability to activate ERK and Akt, even when IGF1R levels are unaltered. Finally, using a viral vector coding for an IR shRNA, we show that downregulation of Insr expression in CP of adult mice has a profound effect on its structure, as demonstrated by MRI and histological technique. Disclosure C.Mazucanti: None. V.L.Kennedy: None. A.Cho: None. Q.Liu: None. J.F.O’connell: None. S.Camandola: None. J.M.Egan: None.

145-OR: Selenite Treatment Impacts Adipocyte Metabolism and Counteracts Detrimental Effects of Diet-Induced Insulin Resistance

The loss of insulin receptor (IR) in white adipose tissue (WAT) is a feature of type 2 diabetes. Previously, we have demonstrated that feeding mice a preventive selenium rich HFD (SRHFD) , while not influencing obesity development, counteracted diet-induced downregulation of IR and insulin resistance. This was caused by selenite-induced Glutathione peroxidase 3 (GPx3) , which enhanced IR expression and concomitant whole-body insulin sensitivity. The positive correlation between GPX3 and IR levels was also present in humans. In the current study, we investigate A) which selenite (Se) transporter is responsible for the beneficial Se-induced metabolism of WAT using of 3T3-L1 cells, and B) the potential therapeutic effect of selenite supplementation in diet-induced obese mice. We find that LDL Receptor Related Protein (LRP) 8 is necessary for Se-induced upregulation of GPx3 and IR expression to modulate insulin action, as siRNA mediated LRP8 knockdown in 3T3-L1 cells abrogates Se-induced insulin-sensitizing effects with e.g. reduced GPx3 and IR expression. To assess the metabolic effect of selenite supplementation in diet-induced obese mice, C57BL/6N mice received a HFD for 6 weeks, which was followed by a SRHFD for further 12 weeks. Unexpectedly, feeding obese mice a SRHFD resulted in a 10% increase in body weight gain compared to the HFD-fed control group. Nevertheless, these mice exhibited signs of improved metabolism with a shift towards smaller adipocytes, as indicator of improved adipocyte metabolism, and decreased plasma insulin levels. Yet, this was accompanied by unaltered inflammation, GPx3 and IR expression. In conclusion, our data suggest that LRP8 represents a novel Se-transporter in adipocytes controlling insulin sensitivity and that established obesity precludes the beneficial increase of Se-induced GPx3 and IR regulation in WAT, highlighting the potential importance of GPx3 as a mediator of adipose tissue insulin sensitivity. Disclosure R.Hauffe: None. M.Rath: None. A.Kleinridders: Other Relationship; Novozymes. Funding Deutsche Forschungsgemeinschaft (KL 2399/4-1) German Ministry of Education and Research BMBF (82DZD00302)

α7nAChR activation protects against oxidative stress, neuroinflammation and central insulin resistance in ICV-STZ induced sporadic Alzheimer's disease

Central insulin resistance is considered as one of the pathological hallmarks of Alzheimer's disease (AD), similar to formation of amyloid plaques and neurofibrillary tangles (NFT). Activation of α7nAChR by GTS-21 has been indicated to reverse peripheral insulin resistance and exert neuroprotection. Therefore, the aim of the present study was to determine the effect of α7nAChR agonist (GTS-21) on intracerebroventricular administration of streptozotocin (ICV-STZ)-induced oxidative stress, neuroinflammation, cholinergic dysfunction, central insulin resistance and cognitive deficits. GTS-21 (1, 4 and 8 mg/kg; i.p.) was administered for 21 days following bilateral ICV-STZ administration (3 mg/kg) in C57BL/6 mice. Neurobehavioral assessments were performed using Morris water maze (MWM) and novel object recognition (NOR). Inflammatory markers (TNF-α, IL-6 and IL-1β) were determined using ELISA. Oxido-nitrosative stress (GSH, MDA and nitrite) and cholinergic activity (acetylcholine esterase and choline acetyltransferase) were estimated in the cortex and hippocampus through biochemical methods. Gene expression of insulin receptor (IR), IRS1, IRS2, BACE1, APP, PI3-K, AKT and GSK3β were determined by q-RT-PCR. ICV-STZ administration induced memory impairment, increased oxidative stress and neuroinflammation, and caused cholinergic dysfunction. Our results demonstrated that activation of α7nAChR by GTS-21 treatment improved memory in MWM and NOR test. Moreover, GTS-21 treatment significantly decreased oxido-nitrosative stress, inflammatory markers and cholinergic dysfunction in cortex and hippocampus. Finally, GTS-21 treatment restored ICV-STZ induced downregulation of IR, IRS1, IRS2, PI3-k, Akt and attenuated GSK3β, APP and BACE-1 indicating improved insulin signalling. Therefore, activation of α7nAChR through GTS-21 might be the potential target for the amelioration of central insulin resistance induced AD.

Abstract P4-02-01: Targeting insulin receptor in estrogen receptor positive breast cancer

Abstract Obesity and metabolic dysfunction are on the rise in the United States. Hyperinsulinemia, frequently seen in these conditions, correlates with an increased risk of development and mortality from estrogen receptor (ER) positive breast cancer. Expression of components of the insulin and insulin-like growth factor (IGF) family of proteins promote cancer cell growth in vitro, link to shorter progression-free survival, and is associates with an increased risk of metastatic disease and death in breast cancer patients. Previously our lab found that development of resistance to the commonly used ER-targeting drug tamoxifen (Tam) in vitro is associated with a loss of the type I IGF receptor expression with an increased dependence on the homologous insulin receptor (IR). These data argue for targeting IR in breast cancer, but concern has been raised due to the potential of disrupting glucose homeostasis in patients with or without existing metabolic disease. To address this concern, a novel insulin-Fc fusion protein (AKS-130) was developed to lower blood glucose levels without causing clinical hypoglycemia with a potential to target tumor IR. AKS-130 was found to downregulate IR expression in models of colorectal cancer (HCT-116) and malignant melanoma (WM266.4). Further, AKS-130 suppressed xenograft growth in fed and fasted states. We examined if AKS-130 had similar effects on ER positive breast cancer cells. To test the hypothesis that resistance to endocrine therapy increases the reliance of ER positive breast cancer cells on IR signaling, we utilized the ER positive breast cancer cell lines (MCF-7L, T47D) and their Tam resistant derivatives (MCF-7L TamR, T47D TamR). Similar to in HCT-116 and WM266.4 cells, we found that AKS-130 is a modest agonist of IR in ER+ breast cancer cells. Exposure to AKS-130 led to a marked reduction in IR expression in both parental and TamR cell lines, and was associated with partially suppressed downstream signaling to Akt. Interestingly, AKS130 induced IR downregulation was inhibited by pretreatment of BMS 536924, a dual IGF1R/IR kinase inhibitor. In vivo, AKS-130 treatment by itself scaled down MCF7L parental xenograft growth as compared to vehicle group, and AKS-130 in combination with Tam trended toward extending time to a tumor size of 500mm3. In MCF7L TamR xenografts, addition of AKS-130 to Tam treatment also trended toward delaying xenograft growth, though it was not statistically significant. Importantly, prolonged treatment with AKS-130 did not lead to significant changes in weight or blood glucose. Taken together these data show that novel agents, such as AKS-130, may serve as way to disrupt IR signaling in cancer cells without affecting host glucose metabolism. Addition of AKS-130 to Tam treatment trended toward delaying xenograft growth though further studies are needed, especially animal model systems of insulin resistance. These data indicate that IR signaling may represent a target to overcome or delay endocrine therapy resistance in breast cancer. Citation Format: Jingran Cao, Lynsey M. Fettig, Kelly LaPara, Xihong Zhang, Sylaja Murikipudi, Andrea R. Delpero, Thomas M. Lancaster, Todd C. Zion, Douglas Yee. Targeting insulin receptor in estrogen receptor positive breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-02-01.

LRG1 is an adipokine that mediates obesity-induced hepatosteatosis and insulin resistance.

Dysregulation in adipokine biosynthesis and function contributes to obesity-induced metabolic diseases. However, the identities and functions of many of the obesity-induced secretory molecules remain unknown. Here, we report the identification of leucine-rich alpha-2-glycoprotein 1 (LRG1) as an obesity-associated adipokine that exacerbates high fat diet-induced hepatosteatosis and insulin resistance. Serum levels of LRG1 were markedly elevated in obese humans and mice compared with their respective controls. LRG1 deficiency in mice greatly alleviated diet-induced hepatosteatosis, obesity, and insulin resistance. Mechanistically, LRG1 bound with high selectivity to the liver and promoted hepatosteatosis by increasing de novo lipogenesis and suppressing fatty acid β-oxidation. LRG1 also inhibited hepatic insulin signaling by downregulating insulin receptor substrates 1 and 2. Our study identified LRG1 as a key molecule that mediates the crosstalk between adipocytes and hepatocytes in diet-induced hepatosteatosis and insulin resistance. Suppressing LRG1 expression and function may be a promising strategy for the treatment of obesity-related metabolic diseases.

Bovine Milk Exosome and miRNA-2478 Enhances Insulin Sensitivity by Upregulating Insulin Receptor and Promotes Glycogen Synthesis in HepG2 Cells

Background: Milk and milk products are a sort of mandatory component of diet world-wide. Milk exosome and its bioactive content especially miRNA has been linked with several metabolic regulatory pathways and diseases. However, there is lack of convincing experimental validation. Recently, we have profiled cow milk exosomal miRNAs and in silico analysis identified insulin receptor (INSR) as potential target of miRNA-2478 which one of the candidate miRNA is encapsulated in cow milk exosomes. Down-regulation of insulin receptor (INSR) in peripheral tissues including liver results in the development of pathogenesis of Type II diabetes. However, role of miRNA-2478 in regulation of insulin signaling has not been studied so far. The main aim of the study was to decipher the role of milk exosomal miR-2478 on its target insulin receptor in HepG2 cells. Methods: The effect of miR-2478 mimic on INSR mRNA and protein expression, glycogen content and enrichment of RNA polymerase II at insulin gene promoter in HepG2 cells was analysed. Findings: Results of the current study showed that there was increased expression of insulin receptor gene at both mRNA and protein level with increased abundance of bta-miR-2478 in HepG2 cells. Similarly, glycogen content was also found to be increased in bta-miR-2478 transfected cells. Results of ChIP assay also showed enrichment of RNA polymerase on insulin receptor promoter in miR-2478 transfected cells as compared to control. Interpretation: In conclusion, bovine milk exosomes and miR-2478 enhanced insulin sensitivity through increased expression of insulin receptor and glycogen synthesis in HepG2 cells. Funding Statement: None. Declaration of Interests: All authors declare they have no conflict of interest. Ethics Approval Statement: Cow (Sahiwal) milk was collected from the healthy and early lactating animals of ICAR-National Dairy Research Institute, Karnal as per the Institute Animal Ethics Guidelines.

GPx3 dysregulation impacts adipose tissue insulin receptor expression and sensitivity

Insulin receptor signaling is crucial for white adipose tissue (WAT) function. Consequently, lack of insulin receptor (IR) in WAT results in a diabetes-like phenotype. Yet, causes for IR downregulation in WAT of patients with diabetes are not well understood. By using multiple mouse models of obesity and insulin resistance, we identify a common downregulation of IR with a reduction of mRNA expression of selenoproteins Txnrd3, Sephs2, and Gpx3 in gonadal adipose tissue. Consistently, GPX3 is also decreased in adipose tissue of insulin-resistant and obese patients. Inducing Gpx3 expression via selenite treatment enhances IR expression via activation of the transcription factor Sp1 in 3T3-L1 preadipocytes and improves adipocyte differentiation and function. Feeding mice a selenium-enriched high-fat diet alleviates diet-induced insulin resistance with increased insulin sensitivity, decreased tissue inflammation, and elevated IR expression in WAT. Again, IR expression correlated positively with Gpx3 expression, a phenotype that is also conserved in humans. Consequently, decreasing GPx3 using siRNA technique reduced IR expression and insulin sensitivity in 3T3-L1 preadipocytes. Overall, our data identify GPx3 as a potentially novel regulator of IR expression and insulin sensitivity in adipose tissue.

Insulin Signaling Via Progesterone-Regulated Insulin Receptor Substrate 2 is Critical for Human Uterine Decidualization.

Decidualization, the process by which fibroblastic human endometrial stromal cells (HESC) differentiate into secretory decidual cells, is a critical event during the establishment of pregnancy. It is dependent on the steroid hormone progesterone acting through the nuclear progesterone receptor (PR). Previously, we identified insulin receptor substrate 2 (IRS2) as a factor that is directly regulated by PR during decidualization. IRS2 is an adaptor protein that functionally links receptor tyrosine kinases, such as insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1R), and their downstream effectors. IRS2 expression was induced in HESC during in vitro decidualization and siRNA-mediated downregulation of IRS2 transcripts resulted in attenuation of this process. Further use of siRNAs targeted to IR or IGF1R transcripts showed that downregulation of IR, but not IGF1R, led to impaired decidualization. Loss of IRS2 transcripts in HESC suppressed phosphorylation of both ERK1/2 and AKT, downstream effectors of insulin signaling, which mediate gene expression associated with decidualization and regulate glucose uptake. Indeed, downregulation of IRS2 resulted in reduced expression and membrane localization of the glucose transporters GLUT1 and GLUT4, resulting in lowered glucose uptake during stromal decidualization. Collectively, these data suggest that the PR-regulated expression of IRS2 is necessary for proper insulin signaling for controlling gene expression and glucose utilization, which critically support the decidualization process to facilitate pregnancy. This study provides new insight into the mechanisms by which steroid hormone signaling intersects with insulin signaling in the uterus during decidualization, which has important implications for pregnancy complications associated with insulin resistance and infertility.

Combination of mulberry leaf and oat bran possessed greater hypoglycemic effect on diabetic mice than mulberry leaf or oat bran alone

• The combined effects of mulberry leaf and oat bran on hyperglycemia were studied. • The combination led to lower blood glucose and insulin levels than ML/OB group. • The combination resulted in more obvious inhibition on the ALT and AST activities. • The co-treatment caused more diverse of gut microbiota compared with ML/OB treatment. • The combination significantly affected the expressions of IR, GK, PCB, PEPCK and PDCK. The aim of this study was to investigate the combined effects of mulberry leaf and oat bran on type 2 diabetes. Co-treatment of diabetic mice with mulberry leaf and oat bran for 28 days led to lower glucose level and better glucose tolerance capacity than either mulberry leaf or oat bran treatment. It was found that this combination resulted in more significant inhibitory effects on alanine transaminase and aspartate transaminase activities. Meanwhile, the enhancement on insulin receptor and glucokinase expressions and down-regulation on pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and pyruvate dehydrogenase complex kinase expressions were also observed. Additionally, the combination increased the gut microbiota diversity, and reshaped the gut microbiota structure . Based on the above data, it is more feasible to affirm that the combined supplementation of mulberry leaf and oat bran is a potential adjuvant on the treatment of diabetes mellitus.

The Different Roles of miRNA-92a-2-5p and let-7b-5p in Mitochondrial Translation in db/db Mice

Excessive reactive oxygen species (ROS) generated in mitochondria is known to be a causal event in diabetic cardiomyopathy. Recent studies suggest that microRNAs (miRNAs) are able to translocate to mitochondria to modulate mitochondrial activities, but the roles of such miRNAs in diabetic cardiomyopathy remain unclear. We observed a marked reduction of mitochondrial gene cytochrome-b (mt-Cytb) in the heart of db/db mice compared with controls. Downregulation of mt-Cytb by small interfering RNA (siRNA) recaptured some key features of diabetes, including elevated ROS production. Microarray revealed that none of the miRNAs were upregulated, but 14 miRNAs were downregulated in mitochondria of db/db heart. miR-92a-2-5p and let-7b-5p targeted mt-Cytb and positively modulated mt-Cytb expression. Re-expression of miR-92a-2-5p and let-7b-5p into cardiomyocytes led to reduced ROS production. Furthermore, recombinant adeno-associated virus (rAAV)-mediated delivery of miR-92a-2-5p, but not let-7b-5p, was sufficient to rescue cardiac diastolic dysfunction in db/db heart. Let-7b-5p not only upregulated mt-Cytb in mitochondria, but also downregulated insulin receptor substrate 1 in cytosol and finally lead to no efficiency for improvement of diastolic dysfunction in db/db mice. Our findings demonstrate that reduced mitochondrial miRNAs contribute to impaired mitochondrial gene expression and elevated ROS production. Re-expression of miR-92a-2-5p enhances mitochondrial translation and reduces ROS production and lipid deposition, which finally rescues diabetic cardiomyopathy.

The hepatic-targeted, resveratrol loaded nanoparticles for relief of high fat diet-induced nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the early stage of many metabolic syndromes. The intervention of NAFLD can prevent its further development into severe metabolic syndromes. Given the inefficiency and side effects of chemical drugs for treating NAFLD, the hepatic-targeted nanocarriers loaded with bioactive compounds may offer a more effective and acceptable strategy for eliminating NAFLD. Here we developed hepatic-targeted oxidized starch-lysozyme (OSL) nanocarriers to specifically deliver resveratrol (Res) to liver tissue in order to maximize its therapeutic efficiency. The hepatic targeting was achieved using covalently conjugated galactose (Gal), which is recognized by the asialoglycoprotein receptors specifically expressed in hepatocytes. In steatotic HepG2 cell model, treatment with hepatic-targeted Gal-OSL/Res nanocarriers enhanced the cellular Res uptake and anti-lipogenesis capabilities, and effectively decreased triglyceride accumulation by modulating AMP-activated protein kinase (AMPK)/silent information regulation 2 homolog 1(SIRT1)/fatty acid synthase (FAS)/sterol regulatory element-binding protein-1c (SREBP1c) signaling pathway. In mice, Gal-OSL increased Res delivery into liver tissues and increased their hepatic effective concentration in liver. Most importantly, Gal-OSL/Res nanocarriers effectively reversed NAFLD and recovered hepatic insulin sensitivity of NAFLD mice to the healthy state. Furthermore, Gal-OSL/Res efficiently ameliorated lipid deposition and insulin resistance by modulating AMPK/SIRT1/FAS/SREBP1c signaling pathway and downregulated insulin receptor substrate-1 (IRS-1) phosphorylation at serine 307 in liver. These findings suggested that the hepatic-targeted Gal-OSL nanocarriers delivering Res could potentially serve as a safe and promising platform for NAFLD and other liver related diseases.

LIF, a Novel Myokine, Protects Against Amyloid-Beta-Induced Neurotoxicity via Akt-Mediated Autophagy Signaling in Hippocampal Cells

BackgroundLeukemia inhibitory factor, a novel myokine, is known to be associated with neural function, but the underlying molecular mechanism remains unclear.MethodsHT-22 mouse hippocampal cells, primary hippocampal cells, and Drosophila Alzheimer’s disease model were used to determine the effect of leukemia inhibitory factor on neurons. Immunoblot analysis and immunofluorescence method were used to analyze biological mechanism.ResultsLeukemia inhibitory factor increased Akt phosphorylation in a phosphoinositide-3-kinase-dependent manner in hippocampal cells. Leukemia inhibitory factor also increased the phosphorylation of the mammalian target of rapamycin and the downstream S6K. Leukemia inhibitory factor stimulated the phosphorylation of signal transducer and activator of transcription via extracellular signal-regulated kinases. Leukemia inhibitory factor increased c-fos expression through both Akt and extracellular signal-regulated kinases. Leukemia inhibitory factor blocked amyloid β-induced neural viability suppression and inhibited amyloid β-induced glucose uptake impairment through the block of amyloid β-mediated insulin receptor downregulation. Leukemia inhibitory factor blocked amyloid β-mediated induction of the autophagy marker, microtubule-associated protein 1A/1B-light chain 3. Additionally, in primary prepared hippocampal cells, leukemia inhibitory factor stimulated Akt and extracellular signal-regulated kinase, demonstrating that leukemia inhibitory factor has physiological relevance in vivo. Suppression of the autophagy marker, light chain 3II, by leukemia inhibitory factor was observed in a Drosophila model of Alzheimer’s disease.ConclusionsThese results demonstrate that leukemia inhibitory factor protects against amyloid β-induced neurotoxicity via Akt/extracellular signal-regulated kinase-mediated c-fos induction, and thus suggest that leukemia inhibitory factor is a potential drug for Alzheimer’s disease.

High fructose diet induces early mortality via autophagy factors accumulation in the rostral ventrolateral medulla as ameliorated by pioglitazone

High fructose ingestion enhances mortality which has been linked to autonomic dysregulation. However, the underlying mechanisms are still largely unknown. In the present study, we demonstrated that 3 months of high fructose diet (HFD) ingestion induced mortality in 18-week-old Wistar Kyoto rats (WKY) during anesthesia. Concurrently, the low frequency (LF) and the high frequency (HF) elements of the power spectral analyses of SBP were increased. Of note, the decreased ratio of LF and HF (LF/HF), an index of sympathetic and parasympathetic balance, suggested an autonomic imbalance. In the rostral ventrolateral medulla (RVLM), a center of sympathetic outflow, the levels of presynaptic (synaptophysin) and postsynaptic (postsynaptic density protein 95 and phospho-Ca2+/calmodulin-dependent protein kinase II) proteins were increased. The down-regulation of insulin receptor β and insulin receptor substrate 1 suggested the status of insulin desensitization. Moreover, the up-regulation of AMP-activated protein kinase and sirtuin 1 suggested the enhancement of energy sensing to activate autophagy. Simultaneously, the accumulations of Beclin-1, ATG12 and LC3B were increased in RVLM. Pioglitazone (PIO), an insulin sensitizer, effectively relieved the accumulation of Beclin-1 and ATG12 as well as the synaptic proteins synchronized with the reverses of insulin and energy sensing signals. Moreover, the autonomic dysregulation and anesthesia-associated mortality were intervened. Together, these results suggested that the HFD-induced, anesthesia-associated mortality rate was related to the autonomic abnormality derived from the RVLM synaptic alteration, which is strongly related to insulin desensitization-associated autophagy. PIO intervened the HFD-induced mortality via reversal of the above-mentioned molecules.

The Influence of Curcumin on the Downregulation of MYC, Insulin and IGF-1 Receptors: A possible Mechanism Underlying the Anti-Growth and Anti-Migration in Chemoresistant Colorectal Cancer Cells.

Background and objectives: Mounting evidence shows that curcumin, a bioactive substance originating from turmeric root, has anticancer properties. Additionally, curcumin prevents the migration and metastasis of tumor cells. However, the molecular mechanism involved in the anti-metastatic action of curcumin is not clear. Most studies have suggested that migration inhibition is related to curcumin’s anti-inflammatory properties. Curcumin possesses a regulatory effect on insulin and insulin-like growth factor-1 (IGF-1) receptors and signaling. Insulin signaling is one of the important pathways involved in tumor initiation and progression; therefore, we proposed that the anti-metastatic effect of curcumin may mediate the downregulation of insulin and insulin-like growth factor-1 receptors. Materials and Methods: Viable resistant cells resulting from treating SW480 cells with 5-fluorouracil (5-FU) were subjected to curcumin treatment to analyze the proliferation and migration capacity in comparison to the untreated counterparts. To test the proliferation and migration potential, MTT, colony formation, and wound healing assays were performed. Real-time polymerase chain reaction (RT-PCR) was performed to measure the mRNA expression of insulin-like growth factor-1R (IGF-1R), insulin receptor (IR), and avian myelocytomatosis virus oncogene cellular homolog (MYC). Results: Our findings showed that curcumin significantly decreased insulin and IGF-1 receptors in addition to MYC expression. Additionally, the downregulation of the insulin and insulin-like growth factor-1 receptors was correlated to a greater decrease in the proliferation and migration of chemoresistant colorectal cancer cells. Conclusions: These results suggest the possible therapeutic effectiveness of curcumin in adjuvant therapy in metastatic colorectal cancer.

Understanding the Role of Cyclin Dependent Kinase 5 (Cdk5) in Insulin Related Neurodegenerative Disease

Cyclin Dependent Kinase 5 (Cdk5) is a member of the cyclin dependent kinase family of proteins that play key roles in the regulation of the cell cycle. The activity of these enzymes is dependent upon association with a cyclin activating partner. Unlike other members of this family, however, Cdk5 appears to play no role in cell cycle regulation. Cdk5 is ubiquitously expressed in all cells. However maximum kinase activity is found in post‐mitotic neurons and glial cells, where Cdk5's cyclin activating partners exhibit high expression. Known substrates of Cdk5 include proteins that modulate cell morphology and motility. Our lab has shown that Cdk5 plays an essential role in the developing nervous system primarily through studies of chemical inhibition of Cdk5 in a neuronal model. Specifically, we employed the well‐known PC12 cell line which can be induced to transdifferentiate into neuronal‐like cells. Inhibition of Cdk5 during this process reduced the neuronal characteristics these cells typically exhibit, mimicking neuronal degradation or degeneration. Multiple published studies support Cdk5's role in the developing mammalian nervous system. Recent investigations have shown an increased correlation between the likelihood of developing neurodegenerative diseases and insulin resistance associated with Type 2 diabetes. Insulin resistance results in the over‐secretion of insulin (hyperinsulinemia) into the blood stream and causes a down regulation of insulin receptors in peripheral tissue. Although acute hyperinsulinemia in the central nervous system (CNS) may have cognitive enhancing effects, chronic hyperinsulinemia appears to be neurotoxic. We are exploring this potential relationship between insulin levels and the neuron by exploiting our neuronal model cell line, PC12. Using this model, we examine the role of normal and aberrant Cdk5 activity in the response of differentiated neuronal‐like PC12 cells to varying concentrations of insulin in culture. Our aim is to test the reports of deregulation of brain insulin signaling as an early marker in AD. Here we show our preliminary results of the transdifferentiation of PC12 cells while Cdk5 activity is manipulated under hyperinsulinemic conditions. Our findings underscore the value of this model as a means to examine the potential role of Cdk5 as a link between AD and Type 2 diabetes. Given the increased Type 2 Diabetes diagnosis and the aging of American society implications for this study are self‐evident.Support or Funding InformationThe Rose M. Badgely Charitable Trust, Joseph Alexander Foundation, Sister Colette Mahoney Science Research Grant and the Marymount Manhattan College Faculty Award.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Maternal Supplementation with β-Carotene During Pregnancy Disturbs Lipid Metabolism and Glucose Homoeostasis in F1 Female Mice.

β-Carotene (BC), a substitute for vitamin A, is widely used for its benefits. The present study investigates whether in-utero BC administration can alter lipid and glucose homoeostasis in offspring. Pregnant mice are supplemented with BC (1 mg kg-1 weight) by oral gavage once every 3 days, for a total of six doses. Increased visceral fat may be caused by up-regulated PPARγ (peroxisome proliferator-activated receptor gamma) and RXRα/β (retinoid X receptors) in liver and adipose tissue, and glucose intolerance is observed in F1 adult females prenatally supplemented with BC, while F1 males do not exhibit these symptoms. In females, increased serum leptin, resistin, and IL-6 and reduced adiponectin, caused by visceral obesity, may result in downregulated insulin receptor signaling in muscle and further account for glucose intolerance. Increased pancreatic β-cell mass might compensate for the downregulated insulin gene (ins2). Increased glucagon and α-cell mass, accompanied by upregulated glucagon gene (gcg), might also be risk factors for the development of diabetes. Maternal supplementation with BC disturbs lipid metabolism and induces glucose intolerance in F1 female mice, suggesting that BC supplementation during pregnancy should be used with caution.

Insulin-like growth factor-II in adipocyte regulation: depot-specific actions suggest a potential role limiting excess visceral adiposity.

The IGF system has an important role in growth and development. IGF-II is a recognized fetal growth promoter. However, its physiological postnatal role remains uncertain, although it is maintained in the circulation at a substantially high level throughout life. IGF-II has been strongly linked to obesity in genetic studies, and more recent evidence suggests a metabolic role. We examined fat depot differences in IGF-II's action on differentiation and metabolism. We speculate a specific effect on visceral adipocytes in relation to the differential distribution of insulin receptors between visceral and subcutaneous fat depots. We used a previously established adipocyte, cell culture system of matched pairs of visceral and subcutaneous fat biopsies from 20 normal weight children undergoing routine surgery for nonmalignant, nonseptic conditions. Preadipocytes were differentiated for 14 days in the presence or absence of IGF-II. Oil Red O staining, Western blotting, and reverse transcription polymerase chain reaction techniques were employed to assess levels of adipogenesis markers and levels of the insulin receptor and insulin receptor isoforms. Our data indicate that IGF-II promotes preadipocyte differentiation in subcutaneous preadipocytes but showed a protective, opposing effect restricting visceral preadipocyte differentiation, confirmed by reductions in the differentiation markers peroxisome proliferator-activated receptor gamma and adiponectin and in triglyceride staining. Additionally, IGF-II reduced mRNA expression of the insulin receptor in adipocytes and downregulated insulin receptor isoform A and glucose transporter 4 abundance and corresponding glucose uptake in visceral adipocytes. In conclusion, IGF-II is a regulator of preadipocyte differentiation and metabolism by acting as a differential modulator of fat accumulation favoring less visceral fat deposition in children.

Molecular signaling mechanisms of renal gluconeogenesis in nondiabetic and diabetic conditions.

The kidneys are as involved as the liver in gluconeogenesis which can significantly contribute to hyperglycemia in the diabetic condition. Substantial evidence has demonstrated the overexpression of rate-limiting gluconeogenic enzymes, especially phosphoenolpyruvate carboxykinase and glucose 6 phosphatase, and the accelerated glucose release both in the isolated proximal tubular cells and in the kidneys of diabetic animal models and diabetic patients. The aim of this review is to provide an insight into the mechanisms that accelerate renal gluconeogenesis in the diabetic conditions and the therapeutic approaches that could affect this process in the kidney. Increase in gluconeogenic substrates, reduced insulin concentration or insulin resistance, downregulation of insulin receptors and insulin signaling, oxidative stress, and inappropriate activation of the renin-angiotensin system are likely to participate in enhancing renal gluconeogenesis in the diabetic milieu. Several studies have suggested that controlling glucose metabolism at the renal level favors effective overall glycemic control in both type 1 and type 2 diabetes. Therefore, renal gluconeogenesis may be a promising target for effective glycemic control as a therapeutic strategy in diabetes.