Type 2 diabetes candidate genes, including PAX5, cause impaired insulin secretion in human pancreatic islets.

Type 2 diabetes (T2D) is caused by insufficient insulin secretion from pancreatic ß cells. To identify candidate genes contributing to T2D pathophysiology, we studied human pancreatic islets from approximately 300 individuals. We found 395 differentially expressed genes (DEGs) in islets from individuals with T2D, including, to our knowledge, novel (OPRD1, PAX5, TET1) and previously identified (CHL1, GLRA1, IAPP) candidates. A third of the identified expression changes in islets may predispose to diabetes, as expression of these genes associated with HbA1c in individuals not previously diagnosed with T2D. Most DEGs were expressed in human ß cells, based on single-cell RNA-Seq data. Additionally, DEGs displayed alterations in open chromatin and associated with T2D SNPs. Mouse KO strains demonstrated that the identified T2D-associated candidate genes regulate glucose homeostasis and body composition in vivo. Functional validation showed that mimicking T2D-associated changes for OPRD1, PAX5, and SLC2A2 impaired insulin secretion. Impairments in Pax5-overexpressing ß cells were due to severe mitochondrial dysfunction. Finally, we discovered PAX5 as a potential transcriptional regulator of many T2D-associated DEGs in human islets. Overall, we have identified molecular alterations in human pancreatic islets that contribute to ß cell dysfunction in T2D pathophysiology.

Dietary substitution of SFA with MUFA within high-fat diets attenuates hyperinsulinaemia and pancreatic islet dysfunction.

Preliminary evidence has suggested that high-fat diets (HFD) enriched with SFA, but not MUFA, promote hyperinsulinaemia and pancreatic hypertrophy with insulin resistance. The objective of this study was to determine whether the substitution of dietary MUFA within a HFD could attenuate the progression of pancreatic islet dysfunction seen with prolonged SFA-HFD. For 32 weeks, C57BL/6J mice were fed either: (1) low-fat diet, (2) SFA-HFD or (3) SFA-HFD for 16 weeks, then switched to MUFA-HFD for 16 weeks (SFA-to-MUFA-HFD). Fasting insulin was assessed throughout the study; islets were isolated following the intervention. Substituting SFA with MUFA-HFD prevented the progression of hyperinsulinaemia observed in SFA-HFD mice (P < 0·001). Glucose-stimulated insulin secretion from isolated islets was reduced by SFA-HFD, yet not fully affected by SFA-to-MUFA-HFD. Markers of ß-cell identity (Ins2, Nkx6.1, Ngn3, Rfx6, Pdx1 and Pax6) were reduced, and islet inflammation was increased (IL-1ß, 3·0-fold, P = 0·007; CD68, 2·9-fold, P = 0·001; Il-6, 1·1-fold, P = 0·437) in SFA-HFD - effects not seen with SFA-to-MUFA-HFD. Switching to MUFA-HFD can partly attenuate the progression of SFA-HFD-induced hyperinsulinaemia, pancreatic inflammation and impairments in ß-cell function. While further work is required from a mechanistic perspective, dietary fat may mediate its effect in an IL-1ß-AMP-activated protein kinase α1-dependent fashion. Future work should assess the potential translation of the modulation of metabolic inflammation in man.

Nutritional Modulation of AMPK-Impact upon Metabolic-Inflammation.

Nutritional status provides metabolic substrates to activate AMP-Activated Protein Kinase (AMPK), the energy sensor that regulates metabolism. Recent evidence has demonstrated that AMPK has wider functions with respect to regulating immune cell metabolism and function. One such example is the regulatory role that AMPK has on NLRP3-inlflammasome and IL-1ß biology. This in turn can result in subsequent negative downstream effects on glucose, lipid and insulin metabolism. Nutrient stress in the form of obesity can impact AMPK and whole-body metabolism, leading to complications such as type 2 diabetes and cancer risk. There is a lack of data regarding the nature and extent that nutrient status has on AMPK and metabolic-inflammation. However, emerging work elucidates to a direct role of individual nutrients on AMPK and metabolic-inflammation, as a possible means of modulating AMPK activity. The posit being to use such nutritional agents to re-configure metabolic-inflammation towards more oxidative phosphorylation and promote the resolution of inflammation. The complex paradigm will be discussed within the context of if/how dietary components, nutrients including fatty acids and non-nutrient food components, such as resveratrol, berberine, curcumin and the flavonoid genistein, modulate AMPK dependent processes relating to inflammation and metabolism.

Fatty Acids and NLRP3 Inflammasome-Mediated Inflammation in Metabolic Tissues.

Worldwide obesity rates have reached epidemic proportions and significantly contribute to the growing prevalence of metabolic diseases. Chronic low-grade inflammation, a hallmark of obesity, involves immune cell infiltration into expanding adipose tissue. In turn, obesity-associated inflammation can lead to complications in other metabolic tissues (e.g., liver, skeletal muscle, pancreas) through lipotoxicity and inflammatory signaling networks. Importantly, although numerous signaling pathways are known to integrate metabolic and inflammatory processes, the nucleotide-binding and oligomerization domain-like receptor, leucine-rich repeat and pyrin domain-containing 3 (NLRP3) inflammasome is now noted to be a key regulator of metabolic inflammation. The NLRP3 inflammasome can be influenced by various metabolites, including fatty acids. Specifically, although saturated fatty acids may promote NLRP3 inflammasome activation, monounsaturated fatty acids and polyunsaturated fatty acids have recently been shown to impede NLRP3 activity. Therefore, the NLRP3 inflammasome and associated metabolic inflammation have key roles in the relationships among fatty acids, metabolites, and metabolic disease. This review focuses on the ability of fatty acids to influence inflammation and the NLRP3 inflammasome across numerous metabolic tissues in the body. In addition, we explore some perspectives for the future, wherein recent work in the immunology field clearly demonstrates that metabolic reprogramming defines immune cell functionality. Although there is a paucity of information about how diet and fatty acids modulate this process, it is possible that this will open up a new avenue of research relating to nutrient-sensitive metabolic inflammation.

A casein hydrolysate protects mice against high fat diet induced hyperglycemia by attenuating NLRP3 inflammasome-mediated inflammation and improving insulin signaling.

SCOPE: Activation of the nod-like receptor protein 3 (NLRP3) inflammasome is required for IL-1ß release and is a key component of obesity-induced inflammation and insulin resistance. This study hypothesized that supplementation with a casein hydrolysate (CH) would attenuate NLRP3 inflammasome mediated IL-1ß secretion in adipose tissue (AT) and improve obesity-induced insulin resistance. METHODS AND RESULTS: J774.2 macrophages were LPS primed (10 ng/mL) and stimulated with adenosine triphosphate (5 mM) to assess NLRP3 inflammasome activity. Pretreatment with CH (1 mg/mL; 48 h) reduced caspase-1 activity and decreased IL-1ß secretion from J774.2 macrophages in vitro. 3T3-L1 adipocytes cultured with conditioned media from CH-pretreated J774.2 macrophages demonstrated increased phosphorylated (p)AKT expression and improved insulin sensitivity. C57BL/6JOLaHsd mice were fed chow or high fat diet (HFD) for 12 wk ± CH resuspended in water (0.5% w/v). CH supplementation improved glucose tolerance in HFD-fed mice as determined by glucose tolerance test. CH supplementation increased insulin-stimulated pAKT protein levels in AT, liver, and muscle after HFD. Cytokine secretion was measured from AT and isolated bone marrow macrophages cultured ex vivo. CH supplementation attenuated IL-1ß, tumor necrosis factor alpha (TNF-α) and IL-6 secretion from AT and IL-1ß, IL-18, and TNF-α from bone marrow macrophages following adenosine triphosphate stimulation ex vivo. CONCLUSION: This novel CH partially protects mice against obesity-induced hyperglycemia coincident with attenuated IL-1ß secretion and improved insulin signaling.

Fatty acids and chronic low grade inflammation associated with obesity and the metabolic syndrome.

The metabolic syndrome is a group of obesity associated metabolic conditions that result in increased risk of cardiovascular disease and type 2 diabetes. Global increases in obesity rates have led to an increase in metabolic syndrome resulting in a demand for increased understanding of the mechanisms involved. This review examines the relationship between adipose tissue biology, lipid metabolism and chronic low grade inflammation relating to obesity and insulin resistance.

Metabolic Inflammation-Differential Modulation by Dietary Constituents.

Obesity arises from a sustained positive energy balance which triggers a pro-inflammatory response, a key contributor to metabolic diseases such as T2D. Recent studies, focused on the emerging area of metabolic-inflammation, highlight that specific metabolites can modulate the functional nature and inflammatory phenotype of immune cells. In obesity, expanding adipose tissue attracts immune cells, creating an inflammatory environment within this fatty acid storage organ. Resident immune cells undergo both a pro-inflammatory and metabolic switch in their function. Inflammatory mediators, such as TNF-α and IL-1ß, are induced by saturated fatty acids and disrupt insulin signaling. Conversely, monounsaturated and polyunsaturated fatty acids do not interrupt metabolism and inflammation to the same extent. AMPK links inflammation, metabolism and T2D, with roles to play in all and is influenced negatively by obesity. Lipid spillover results in hepatic lipotoxicity and steatosis. Also in skeletal muscle, excessive FFA can impede insulin's action and promote inflammation. Ectopic fat can also affect pancreatic ß-cell function, thereby contributing to insulin resistance. Therapeutics, lifestyle changes, supplements and dietary manipulation are all possible avenues to combat metabolic inflammation and the subsequent insulin resistant state which will be explored in the current review.

Monounsaturated fatty acid-enriched high-fat diets impede adipose NLRP3 inflammasome-mediated IL-1ß secretion and insulin resistance despite obesity.

Saturated fatty acid (SFA) high-fat diets (HFDs) enhance interleukin (IL)-1ß-mediated adipose inflammation and insulin resistance. However, the mechanisms by which different fatty acids regulate IL-1ß and the subsequent effects on adipose tissue biology and insulin sensitivity in vivo remain elusive. We hypothesized that the replacement of SFA for monounsaturated fatty acid (MUFA) in HFDs would reduce pro-IL-1ß priming in adipose tissue and attenuate insulin resistance via MUFA-driven AMPK activation. MUFA-HFD-fed mice displayed improved insulin sensitivity coincident with reduced pro-IL-1ß priming, attenuated adipose IL-1ß secretion, and sustained adipose AMPK activation compared with SFA-HFD-fed mice. Furthermore, MUFA-HFD-fed mice displayed hyperplastic adipose tissue, with enhanced adipogenic potential of the stromal vascular fraction and improved insulin sensitivity. In vitro, we demonstrated that the MUFA oleic acid can impede ATP-induced IL-1ß secretion from lipopolysaccharide- and SFA-primed cells in an AMPK-dependent manner. Conversely, in a regression study, switching from SFA- to MUFA-HFD failed to reverse insulin resistance but improved fasting plasma insulin levels. In humans, high-SFA consumers, but not high-MUFA consumers, displayed reduced insulin sensitivity with elevated pycard-1 and caspase-1 expression in adipose tissue. These novel findings suggest that dietary MUFA can attenuate IL-1ß-mediated insulin resistance and adipose dysfunction despite obesity via the preservation of AMPK activity.

Interactions between differential fatty acids and inflammatory stressors-impact on metabolic health.

Current interest in obesity has established a clear link between diets high in fat and metabolic complications such as Type 2 Diabetes. Dietary fats and their metabolites act as stressors to induce a pro-inflammatory immune response which dysregulates many essential metabolic functions. Recent research suggests that different dietary fats may have varying inflammatory potentials. However the molecular mechanisms involved in the cross talk between dietary fat composition and the 'immuno-metabolism' remain enigmatic. It is probable that lipids, and their derivatives, differentially regulate IL-1ß activation and inflammatory signaling via the NLRP3 inflammasome complex. Also from the translational perspective, certain nutrient sensitive genotypes and potential gene nutrient interactions offer the possibility to reduce inflammation through personalized nutrition approaches.

Endogenous oils derived from human adipocytes are potent adjuvants that promote IL-1α-dependent inflammation.

Obesity is characterized by chronic inflammation associated with neutrophil and M1 macrophage infiltration into white adipose tissue. However, the mechanisms underlying this process remain largely unknown. Based on the ability of oil-based adjuvants to induce immune responses, we hypothesized that endogenous oils derived from necrotic adipocytes may function as an immunological "danger signal." Here we show that endogenous oils of human origin are potent adjuvants, enhancing antibody responses to a level comparable to Freund's incomplete adjuvant. The endogenous oils were capable of promoting interleukin (IL)-1α-dependent recruitment of neutrophils and M1-like macrophages, while simultaneously diminishing M2-like macrophages. We found that endogenous oils from subcutaneous and omental adipocytes, and from healthy and unhealthy obese individuals, promoted comparable inflammatory responses. Furthermore, we also confirmed that white adipocytes in visceral fat of metabolically unhealthy obese (MUO) individuals are significantly larger than those in metabolically healthy obese individuals. Since adipocyte size is positively correlated with adipocyte death, we propose that endogenous oils have a higher propensity to be released from hypertrophied visceral fat in MUO individuals and that this is the key factor in driving inflammation. In summary, this study shows that adipocytes contain a potent oil adjuvant which drives IL-1α-dependent proinflammatory responses in vivo.