Hyperinsulinemia is Associated with Increased Soluble Insulin Receptors Release from Hepatocytes

Influence of Insulin Receptor Single Nucleotide Polymorphisms on Glycaemic Control and Formation of Anti-Insulin Antibodies in Diabetes Mellitus

Single nucleotide polymorphisms (SNPs) in insulin and insulin receptor genes may influence the interaction between the two molecules, as may anti-insulin antibodies (IAs), commonly found in patients with type 1 diabetes mellitus (T1D) or type 2 diabetes mellitus (T2D) treated with exogenous insulin. We examined the impact of two SNPs in the human insulin gene (INS), rs3842752 and rs689, and two in the insulin receptor gene (INSR) rs2245649 and rs2229429, on disease susceptibility, glycaemic control, and IAs formation in 100 T1D patients and 101 T2D patients treated with insulin. 79 individuals without diabetes were typed as healthy controls. The minor alleles of rs3842752 and rs689 in INS protected against T1D (OR: 0.50, p = 0.01 and OR: 0.44; p = 0.002, respectively). The minor alleles of both rs2245649 and rs2229429 in INSR were risk factors for poor glycaemic control (HbA1c ≥ 80 mmol/mol) in T1D (OR: 5.35, p = 0.009 and OR: 3.10, p = 0.01, respectively). Surprisingly, the minor alleles of rs2245649 and rs2229429 in INSR associated strongly with the absence of IAs in T1D (OR = 0.28, p = 0.008 and OR = 0.30, p = 0.002, respectively). In conclusion, the minor alleles of the investigated INS SNPs protect against T1D, and the minor alleles of the investigated INSR SNPs are associated with poor glycaemic control and the absence of IAs in T1D.

The mediating role of vascular inflammation in traffic-related air pollution associated changes in insulin resistance in healthy adults

AIM

The precise pathophysiologic pathway linking traffic-related air pollution (TRAP) to diabetes mellitus is not well elucidated. We aimed to investigate whether activation of vascular inflammation can be a mechanistic linkage between ambient TRAP and insulin resistance.

METHODS

Study outcomes were determined by assessing a series of circulating biomarkers indicative of insulin resistance and vascular inflammation among 73 healthy adults who underwent repeated clinical visits in Beijing, China, 2014-2016. Concomitantly, concentrations of ambient TRAP indices, including particulate matter in diameter <2.5 μm (PM_2.5), particles in size fractions of 5-560 nm, black carbon, carbon monoxide, nitrogen dioxide, and oxides of nitrogen, were continuously monitored.

RESULTS

Participants experienced extremely high levels of TRAP exposures, with mean (standard deviation) PM_2.5 concentrations of 91.8 (48.3) μg/m³, throughout the study. We found that interquartile range increases in exposure to moving average concentrations of various TRAP indices at prior up to 7 days were associated with significant elevations of 8.9-49.6% in insulin levels. Higher pollutant levels were also related to worsening metrics of insulin resistance (soluble insulin receptor ectodomain, adipokines, and homeostasis model assessment of insulin resistance) and heightened vascular inflammatory responses, particularly disruptions of the receptor activator of nuclear factor κB ligand/osteoprotegerin system balance and elevations of monocyte/macrophage and T cell activation markers. Mediation analyses showed that activation of vascular inflammation could explain up to 66% of the alterations in metrics of insulin resistance attributable to air pollution.

CONCLUSION

Our results suggest that ambient traffic pollution exposure was capable of promoting insulin resistance possibly via generating vascular inflammation.

Combustion-derived particulate organic matter associated with hemodynamic abnormality and metabolic dysfunction in healthy adults

Epidemiological evidence on cardiometabolic health of particulate organic matter (POM) and its sources is sparse. In a panel of 73 healthy adults in Beijing, China, daily concentrations of ambient fine particulate matter-bound polycyclic aromatic hydrocarbons (PAHs) and n-alkanes were measured throughout the study period, and Positive Matrix Factorization approach was used to identity PAHs sources. Linear mixed-effect models and mediation analyses were applied to examine the associations and potential interlink pathways between POM and biomarkers indicative of hemodynamics, insulin resistance, vascular calcification and immune inflammation. We found that significant alterations in cardiometabolic measures were associated with POM exposures. In specific, interquartile range increases in PAHs concentrations at prior up to 9 days were observed in association with significant elevations of 2.6-2.9% in diastolic blood pressure, 6.6-8.1% in soluble ST2, 10.5-14.5% in insulin, 40.9-45.7% in osteoprotegerin, and 36.3-48.7% in interleukin-17A. Greater associations were generally observed for PAHs originating from traffic emissions and coal burning. Mediation analyses revealed that POM exposures may prompt the genesis of hemodynamic abnormalities, possibly via worsening insulin resistance and calcification potential. These findings suggested that cardiometabolic health benefits would be achieved by reducing PM from combustion emissions.

Hyperglycemia, Insulin, and Insulin Resistance in Sepsis

Critically ill patients frequently have hyperglycemia. This event may reflect severe stress with an imbalance between anabolic hormones and catabolic hormones. Alternatively, it may reflect alterations in either insulin levels or insulin function. Insulin is a pleiotropic hormone with multiple important metabolic effects. In patients with sepsis, insulin levels are increased but insulin sensitivity is decreased. However, there is variability in insulin sensitivity, and this creates variability in glucose levels and insulin requirements and increases the frequency of hypo- and hyperglycemia. The factors that influence insulin sensitivity are complex and include inhibition of tyrosine kinase activity of the beta subunit, increased proteolytic activity resulting in loss of receptors from the plasma membrane, and possibly the transfer of insulin receptors into the nucleus where they bind to gene promoters. Better understanding of the role of insulin in critically ill patients requires prospective studies measuring insulin levels in various patient groups and the development of a simple measure of insulin sensitivity.

Glucose, insulin, insulin receptor subunits α and β in normal and spontaneously diabetic and obese ob/ob and db/db infertile mouse testis and hypophysis

BACKGROUND

Type 2 diabetes touches young subjects of reproductive age in epidemic proportion. This study assesses glucose, total InsulinT, Insulin2 and insulin receptor subunits α and β in testis during mouse development then, in the spontaneously type 2 diabetes models associated with infertility db/db and ob/ob mice. IR-β and α were also assessed in spermatozoa (SPZ), anterior pituitary (AP) and serum.

METHODS

Serum and tissue glucose were measured with enzymatic colorimetric assays and InsulinT and Insulin2 by ELISAs in serum, interstitial tissue- (ITf) and seminiferous tubule (STf) fractions in14- > 60-day-old normal and db/db, ob/ob and wild type (WT) mice. IR subunits were assessed by immunoblotting in tissues and by immunoprecipitation followed by immunoblotting in serum.

RESULTS

Development: Glucose increased in serum, ITf and STf. InsulinT and Insulin2 dropped in serum; both were higher in STf than in ITf. In > 60-day-old mouse ITf, insulinT rose whereas Insulin2 decreased; InsulinT and Insulin2 rose concurrently in STf. Glucose and insulin were high in > 60-day-old ITf; in STf high insulin2 accompanied low glucose. One hundred ten kDa IR-β peaked in 28-day-old ITf and 14-day-old STf. One hundred thirty five kDa IR-α was high in ITf but decreased in STf. Glucose escalated in db/db and ob/ob sera. Glucose doubled in ITf while being halved in STf in db/db mice. Glucose significantly dropped in db/db and ob/ob mice spermatozoa. InsulinT and Insulin2 rose significantly in the serum, ITf and STf in db/db and ob/ob mice. One hundred ten kDa IR-β and 135 kDa IR-α decreased in db/db and ob/ob ITf. Only 110 kDa IR-β dropped in db/db and ob/ob STf and AP. One hundred ten kDa IR-β fell in db/db and ob/ob SPZ. One hundred ten kDa sIR-α rose in the db/db and ob/ob mouse sera.

CONCLUSION

Insulin regulates glucose in tubules not in the interstitium. The mouse interstitium contains InsulinT and Insulin2 whereas tubules contain Insulin2. Decreased 110 kDa IR-β and 135 kDa IR-α in the db/db and ob/ob interstitial tissue suggest a loss of active receptor sites that could alter the testicular cell insulin binding and response to the hormone. Decreased IR-β levels were insufficient to stimulate downstream effectors in AP and tubules. IR-α shedding increased in db/db and ob/ob mice.

Inhibition of Serine Protease Activity Protects Against High Fat Diet-Induced Inflammation and Insulin Resistance

Recent evidence suggests that enhanced protease-mediated inflammation may promote insulin resistance and result in diabetes. This study tested the hypothesis that serine protease plays a pivotal role in type 2 diabetes, and inhibition of serine protease activity prevents hyperglycemia in diabetic animals by modulating insulin signaling pathway. We conducted a single-center, cross-sectional study with 30 healthy controls and 57 patients with type 2 diabetes to compare plasma protease activities and inflammation marker between groups. Correlations of plasma total and serine protease activities with variables were calculated. In an in-vivo study, LDLR^−/− mice were divided into normal chow diet, high-fat diet (HFD), and HFD with selective serine protease inhibition groups to examine the differences of obesity, blood glucose level, insulin resistance and serine protease activity among groups. Compared with controls, diabetic patients had significantly increased plasma total protease, serine protease activities, and also elevated inflammatory cytokines. Plasma serine protease activity was positively correlated with body mass index, hemoglobin A1c, homeostasis model assessment-insulin resistance index (HOMA-IR), tumor necrosis factor-α, and negatively with adiponectin concentration. In the animal study, administration of HFD progressively increased body weight, fasting glucose level, HOMA-IR, and upregulated serine protease activity. Furthermore, in-vivo serine protease inhibition significantly suppressed systemic inflammation, reduced fasting glucose level, and improved insulin resistance, and these effects probably mediated by modulating insulin receptor and cytokine expression in visceral adipose tissue. Our findings support the serine protease may play an important role in type 2 diabetes and suggest a rationale for a therapeutic strategy targeting serine protease for clinical prevention of type 2 diabetes.

Altered Extracellular Vesicle Concentration, Cargo, and Function in Diabetes

Type 2 diabetes is a chronic age-associated degenerative metabolic disease that reflects relative insulin deficiency and resistance. Extracellular vesicles (EVs) (exosomes, microvesicles, and apoptotic bodies) are small (30-400 nm) lipid-bound vesicles capable of shuttling functional proteins, nucleic acids, and lipids as part of intercellular communication systems. Recent studies in mouse models and in cell culture suggest that EVs may modulate insulin signaling. Here, we designed cross-sectional and longitudinal cohorts of euglycemic participants and participants with prediabetes or diabetes. Individuals with diabetes had significantly higher levels of EVs in their circulation than euglycemic control participants. Using a cell-specific EV assay, we identified that levels of erythrocyte-derived EVs are higher with diabetes. We found that insulin resistance increases EV secretion. Furthermore, the levels of insulin signaling proteins were altered in EVs from individuals with high levels of insulin resistance and β-cell dysfunction. Moreover, EVs from individuals with diabetes were preferentially internalized by circulating leukocytes. Cytokine levels in the media and in EVs were higher from monocytes incubated with diabetic EVs. Microarray of these leukocytes revealed altered gene expression pathways related to cell survival, oxidative stress, and immune function. Collectively, these results suggest that insulin resistance increases the secretion of EVs, which are preferentially internalized by leukocytes, and alters leukocyte function.

The beta secretase BACE1 regulates the expression of insulin receptor in the liver

Insulin receptor (IR) plays a key role in the control of glucose homeostasis; however, the regulation of its cellular expression remains poorly understood. Here we show that the amount of biologically active IR is regulated by the cleavage of its ectodomain, by the β-site amyloid precursor protein cleaving enzyme 1 (BACE1), in a glucose concentration-dependent manner. In vivo studies demonstrate that BACE1 regulates the amount of IR and insulin signaling in the liver. During diabetes, BACE1-dependent cleavage of IR is increased and the amount of IR in the liver is reduced, whereas infusion of a BACE1 inhibitor partially restores liver IR. We suggest the potential use of BACE1 inhibitors to enhance insulin signaling during diabetes. Additionally, we show that plasma levels of cleaved IR reflect IR isoform A expression levels in liver tumors, which prompts us to propose that the measurement of circulating cleaved IR may assist hepatic cancer detection and management.

Proteolytic receptor cleavage in the pathogenesis of blood rheology and co-morbidities in metabolic syndrome. Early forms of autodigestion

Abnormal blood rheological properties seldom occur in isolation and instead are accompanied by other complications, often designated as co-morbidities. In the metabolic syndrome with complications like hypertension, diabetes and lack of normal microvascular blood flow, the underlying molecular mechanisms that simultaneously lead to elevated blood pressure and diabetes as well as abnormal microvascular rheology and other cell dysfunctions have remained largely unknown. In this review, we propose a new hypothesis for the origin of abnormal cell functions as well as multiple co-morbidities. Utilizing experimental models for the metabolic disease with diverse co-morbidities we summarize evidence for the presence of an uncontrolled extracellular proteolytic activity that causes ectodomain receptor cleavage and loss of their associated cell function. We summarize evidence for unchecked degrading proteinase activity, e.g. due to matrix metalloproteases, in patients with hypertension, Type II diabetes and obesity, in addition to evidence for receptor cleavage in the form of receptor fragments and decreased extracellular membrane expression levels. The evidence suggest that a shift in blood rheological properties and other co-morbidities may in fact be derived from a common mechanism that is due to uncontrolled proteolytic activity, i.e. an early form of autodigestion. Identification of the particular proteases involved and the mechanisms of their activation may open the door to treatment that simultaneously targets multiple co-morbidities in the metabolic syndrome.

Association of MMP-8 with obesity, smoking and insulin resistance

BACKGROUND

Obesity has been recognized as a state of subclinical inflammation resulting in a loss of insulin receptors and decreased insulin sensitivity. We here studied in vivo the role of circulating matrix metalloproteinase-8 (MMP-8) among young healthy twin adults. Also, in vitro analysis of the cleavage of human insulin receptor (INSR) by MMP-8 was investigated as well its inhibition by doxycycline and other MMP-8 inhibitor, Ilomastat/GM6001, which are broad-spectrum MMP inhibitors.

MATERIALS AND METHODS

We analysed serum MMP-8 levels by a time-resolved immunofluorometric assay in obese (n = 34), overweight (n = 76) and normal weight (n = 130) twin individuals. The effect of MMP-8 on INSR and the effects of synthetic MMP-8 inhibitors, doxycycline and Ilomastat/GM6001, were studied by SDS-PAGE.

RESULTS

We found that in obese individuals relative to normal weight individuals, the serum MMP-8 levels and MMP-8/TIMP-1 ratio were significantly increased (P = 0·0031 and P = 0·031, respectively). Among normal weight and obese individuals, also smoking significantly increases serum MMP-8 and MMP-8/TIMP-1 ratio. In vitro, we found that INSR was degraded by MMP-8 and this was inhibited by doxycycline and Ilomastat/GM6001.

CONCLUSIONS

Obesity associated with elevated circulating MMP-8 found among young adults may contribute to progression of insulin resistance by cleaving INSR. This INSR cleavage by MMP-8 can be inhibited by synthetic MMP-8 inhibitors such as doxycycline. In addition to obesity, also smoking independently explained increased MMP-8 levels. Our results suggest that MMP-8 is an essential mediator in systemic subclinical inflammatory response in obesity, and a potential drug target.

Anti-Diabetic Effect of Aster sphathulifolius in C57BL/KsJ-db/db Mice

In this study, we investigated the anti-diabetic effect of Aster sphathulifolius (AS) extract in C57BL/KsJ-db/db mice. The db/db mice were orally administered with AS 50% ethanol extract at concentrations of 50, 100, and 200 mg/kg/day (db/db-AS50, db/db-AS100, and db/db-AS200, respectively) for 10 weeks. Food and water intake, fasting blood glucose concentrations, blood glycosylated hemoglobin levels, and plasma insulin levels were significantly lower in the db/db-AS200 group than in the vehicle-treated db/db group; whereas glucose tolerance was significantly improved in the db/db-AS200 group. Moreover, AS dose dependently increased both insulin receptor substrate 1 and glucose transporter type 4 expression in skeletal muscle, significantly increased glucokinase expression, and decreased glucose 6-phosphatase and phosphoenolpyruvate carboxykinase expressions in the liver. The expressions of transcription factors, such as sterol-regulatory element-binding protein, peroxisome proliferator-activated receptor γ, and adipocyte protein 2, were upregulated in adipose tissue. Furthermore, immunohistochemical analysis showed that AS upregulated insulin production by increasing pancreatic β-cell mass. In summary, AS extract normalized hyperglycemia by multiple mechanisms: inhibition of glyconeogenesis, acceleration of glucose metabolism and lipid metabolism, and increase of glucose uptake. Using in vivo assays, this study has shown the potential of AS as a medicinal food and suggests the efficacy of AS for the use of prevention of diabetes.

Human GH receptor-IGF-1 receptor interaction: implications for GH signaling

GH signaling yields multiple anabolic and metabolic effects. GH binds the transmembrane GH receptor (GHR) to activate the intracellular GHR-associated tyrosine kinase, Janus kinase 2 (JAK2), and downstream signals, including signal transducer and activator of transcription 5 (STAT5) activation and IGF-1 gene expression. Some GH effects are partly mediated by GH-induced IGF-1 via IGF-1 receptor (IGF-1R), a tyrosine kinase receptor. We previously demonstrated in non-human cells that GH causes formation of a GHR-JAK2-IGF-1R complex and that presence of IGF-1R (even without IGF-1 binding) augments proximal GH signaling. In this study, we use human LNCaP prostate cancer cells as a model system to further study the IGF-1R's role in GH signaling. GH promoted JAK2 and GHR tyrosine phosphorylation and STAT5 activation in LNCaP cells. By coimmunoprecipitation and a new split luciferase complementation assay, we find that GH augments GHR/IGF-1R complex formation, which is inhibited by a Fab of an antagonistic anti-GHR monoclonal antibody. Short hairpin RNA-mediated IGF-1R silencing in LNCaP cells reduced GH-induced GHR, JAK2, and STAT5 phosphorylation. Similarly, a soluble IGF-1R extracellular domain fragment (sol IGF-1R) interacts with GHR in response to GH and blunts GH signaling. Sol IGF-1R also markedly inhibits GH-induced IGF-1 gene expression in both LNCaP cells and mouse primary osteoblast cells. On the basis of these and other findings, we propose a model in which IGF-1R augments GH signaling by allowing a putative IGF-1R-associated molecule that regulates GH signaling to access the activated GHR/JAK2 complex and envision sol IGF-1R as a dominant-negative inhibitor of this IGF-1R-mediated augmentation. Physiological implications of this new model are discussed.