Combined effects of PPARγ2 P12A and PPARα L162V polymorphisms on glucose and insulin homeostasis: the Québec Family Study

Association between Genotype and the Glycemic Response to an Oral Glucose Tolerance Test: A Systematic Review

The inter-individual variability of metabolic response to foods may be partly due to genetic variation. This systematic review aims to assess the associations between genetic variants and glucose response to an oral glucose tolerance test (OGTT). Three databases (PubMed, Web of Science, Embase) were searched for keywords in the field of genetics, OGTT, and metabolic response (PROSPERO: CRD42021231203). Inclusion criteria were available data on single nucleotide polymorphisms (SNPs) and glucose area under the curve (gAUC) in a healthy study cohort. In total, 33,219 records were identified, of which 139 reports met the inclusion criteria. This narrative synthesis focused on 49 reports describing gene loci for which several reports were available. An association between SNPs and the gAUC was described for 13 gene loci with 53 different SNPs. Three gene loci were mostly investigated: transcription factor 7 like 2 (TCF7L2), peroxisome proliferator-activated receptor gamma (PPARγ), and potassium inwardly rectifying channel subfamily J member 11 (KCNJ11). In most reports, the associations were not significant or single findings were not replicated. No robust evidence for an association between SNPs and gAUC after an OGTT in healthy persons was found across the identified studies. Future studies should investigate the effect of polygenic risk scores on postprandial glucose levels.

Kaempferide improves glycolipid metabolism disorder by activating PPARγ in high-fat-diet-fed mice

AIMS

Kaempferide (Ka, 3,5,7-trihydroxy-4'-methoxyflavone), an active ingredient of Tagetes erecta L., has been demonstrated to possess many pharmacological effects, including antioxidant, anti-inflammation, anticancer and antihypertension in previous study. However, there is no evidence of Ka on metabolic disorder in former studies. This study investigated the effects of Ka on glycolipid metabolism and explored the underlying mechanisms of action in vivo and vitro.

MATERIALS AND METHODS

The mouse model of glycolipid metabolism disorder was induced by high-fat diet (HFD). The effects of Ka were evaluated on bodyweight, lipid metabolism and glucose metabolism. Hypolipidemic effect was examined by blood sample analysis. The hypoglycemic effect was detected by several indicators, like blood glucose, serum insulin, HOMA index and intraperitoneal glucose tolerance tests (IPGTT). The signaling pathways of lipid metabolism (PPARγ/LXRα/ABCA1) and glucose metabolism (PPARγ/PI3K/AKT) were evaluated using Real-Time PCR and Western blot. The primary culture of hepatocyte was prepared to confirm the target of Ka by co-culturing with PPARγ agonist or inhibitor.

KEY FINDINGS

The HFD mice developed obesity, hyperlipidemia, hyperglycemia and insulin resistance. Administration of Ka at a dose of 10 mg/kg.BW for 16 weeks effectively attenuated these changes. Further studies revealed the hypolipidemic and hypoglycemic effects of Ka depended on the activation of PPARγ/LXRα/ABCA1 and PPARγ/PI3K/AKT pathways, respectively. The primary hepatocyte test, co-cultured with PPARγ agonists or inhibitors, further confirmed the above signaling pathway and key protein.

SIGNIFICANCE

These results suggested that Ka played an important role in improving glycolipid metabolism disorder. These favorable effects were causally associated with anti-obesity. The underlying mechanisms might have to do with the activation of the PPARγ and its downstream signaling pathway. Our study helped to understand the pharmacological actions of Ka, and played a role for Ka in the effective treatment of obesity, diabetes, nonalcoholic hepatitis and other metabolic diseases.

Monogenic Diabetes: What It Teaches Us on the Common Forms of Type 1 and Type 2 Diabetes

To date, more than 30 genes have been linked to monogenic diabetes. Candidate gene and genome-wide association studies have identified > 50 susceptibility loci for common type 1 diabetes (T1D) and approximately 100 susceptibility loci for type 2 diabetes (T2D). About 1-5% of all cases of diabetes result from single-gene mutations and are called monogenic diabetes. Here, we review the pathophysiological basis of the role of monogenic diabetes genes that have also been found to be associated with common T1D and/or T2D. Variants of approximately one-third of monogenic diabetes genes are associated with T2D, but not T1D. Two of the T2D-associated monogenic diabetes genes-potassium inward-rectifying channel, subfamily J, member 11 (KCNJ11), which controls glucose-stimulated insulin secretion in the β-cell; and peroxisome proliferator-activated receptor γ (PPARG), which impacts multiple tissue targets in relation to inflammation and insulin sensitivity-have been developed as major antidiabetic drug targets. Another monogenic diabetes gene, the preproinsulin gene (INS), is unique in that INS mutations can cause hyperinsulinemia, hyperproinsulinemia, neonatal diabetes mellitus, one type of maturity-onset diabetes of the young (MODY10), and autoantibody-negative T1D. Dominant heterozygous INS mutations are the second most common cause of permanent neonatal diabetes. Moreover, INS gene variants are strongly associated with common T1D (type 1a), but inconsistently with T2D. Variants of the monogenic diabetes gene Gli-similar 3 (GLIS3) are associated with both T1D and T2D. GLIS3 is a key transcription factor in insulin production and β-cell differentiation during embryonic development, which perturbation forms the basis of monogenic diabetes as well as its association with T1D. GLIS3 is also required for compensatory β-cell proliferation in adults; impairment of this function predisposes to T2D. Thus, monogenic forms of diabetes are invaluable "human models" that have contributed to our understanding of the pathophysiological basis of common T1D and T2D.

Interaction Effects of the Leu162Val PPAR α and Pro12Ala PPAR γ 2 Gene Variants with Renal Function in Metabolic Syndrome Population

Leu162Val PPARα and Pro12Ala PPARγ2 were investigated for their individual and their interactive impact on MS and renal functionality (RF). 522 subjects were investigated for biochemical and anthropometric measurements. The diagnosis of MS was based on the IDF definition (2009). The HOMA 2 was used to determine HOMA-β, HOMA-S and HOMA-IR from FPG and FPI concentrations. RF was assessed by estimating the GFR. PCR-RFLP was performed for DNA genotyping. Allele frequencies were 0.845 for Pro and 0.155 for Ala, and were 0.915 for Leu and 0.085 for Val. We showed that carriers of the PPARα Val 162 allele had lower urea, UA and higher GFR compared to those homozygous for the Leu162 allele. Subjects carried by PPARγ2Ala allele had similar results. They also had reduced FPG, FPI and HOMA-IR, and elevated HOMA-β and HOMA-S compared to those homozygous for the Pro allele. Subjects were divided into 4 groups according to the combinations of genetic alleles of the 2 polymorphisms. Subjects carrying the Leu/Val with an Ala allele had lower FPG, PPI, HOMA-IR, urea, UA levels, higher HOMA-β, HOMA-S and GFR than different genotype combinations. Leu162Val PPARα and Pro12Ala PPARγ2 can interact with each other to modulate glucose and insulin homeostasis and expand their association with overall better RF.

PPARγ2 polymorphism and human health

The nuclear hormone receptor peroxisome proliferator activated receptor gamma (PPARγ) is an important transcription factor regulating adipocyte differentiation, lipid and glucose homeostasis, and insulin sensitivity. Numerous genetic mutations of PPARγ have been identified and these mutations positively or negatively regulate insulin sensitivity. Among these, a relatively common polymorphism of PPARγ, Pro12Ala of PPARγ2, the isoform expressed only in adipose tissue has been shown to be associated with lower body mass index, enhanced insulin sensitivity, and resistance to the risk of type 2 diabetes in human subjects carrying this mutation. Subsequent studies in different ethnic populations, however, have revealed conflicting results, suggesting a complex interaction between the PPARγ2 Pro12Ala polymorphism and environmental factors such as the ratio of dietary unsaturated fatty acids to saturated fatty acids and/or between the PPARγ2 Pro12Ala polymorphism and genetic factors such as polymorphic mutations in other genes. In addition, this polymorphic mutation in PPARγ2 is associated with other aspects of human diseases, including cancers, polycystic ovary syndrome, Alzheimer disease and aging. This review will highlight findings from recent studies.

Peroxisome proliferator-activated receptor-alpha (PPARA) genetic polymorphisms and breast cancer risk: a Long Island ancillary study

Peroxisome proliferator-activated receptor-alpha (PPARA) has been shown to increase fatty acid oxidation and decrease cytokine levels and has been implicated in insulin production. Genetic variants of PPARA have been associated with cardiovascular disease, obesity and type II diabetes mellitus. Although no research to date has investigated the possible link between PPARA and breast cancer, the function of this gene suggests that it could play a role in breast cancer development. Six PPARA polymorphisms were evaluated in association with incident breast cancer in a population-based case-control study (n = 1073 cases and n = 1112 controls) using unconditional logistic and multilevel regression and haplotype-based analyses. The odds of breast cancer were doubled among women with PPARA polymorphism rs4253760 (odds ratio = 1.97 for rare versus common homozygote alleles; 95% confidence interval: 1.14, 3.43). This association remained constant with the inclusion of all interrogated polymorphisms studied in hierarchical models. No additive interactions with body mass index or weight gain were present, but there was some evidence of interaction between PPARA variants and aspirin use, defined as use at least once per week for 6 months or longer. Fourteen haplotypes were imputed with frequencies >1% among postmenopausal women, but no statistically significant differences in haplotype frequencies between cases and controls were evident. Our results are the first to evaluate the relationship between PPARA and breast cancer incidence and suggest that replication in an independent cohort is warranted.

Searching for alleles associated with complicated outcomes after burn injury

Sepsis is a serious and growing health problem among patients admitted to intensive care units. When accompanied by organ failure, sepsis carries a 30-50% case-fatality rate. Although our understanding of burn pathophysiology has grown in recent years, we are still unable to identify accurately patients who are at increased risk for infectious complications and death. Genetic predisposition is likely to explain a portion of this variation. Understanding which genes and allelic variants contribute to disease risk would increase our ability to predict who is at increased risk and intervene accordingly, as well as identify molecular targets for novel and individualized therapies. Several obstacles exist to identification of which specific alleles and loci contribute to patient risk, including achievement of sufficient statistical power, population admixture and epistatic interaction among multiple genes and environmental factors. Although increasing sample size will resolve most, if not all, of these issues, slow patient accrual often makes this solution impractical for a single institution within a reasonable timeframe. This situation is complicated by the fact that traditional analysis methods perform poorly in the face of data sparseness. Identification of risk factors for severe sepsis and death after burn injury will likely require collaborative patient enrollment as well as development of advanced analytical methodologies. While overcoming these obstacles may prove difficult, the effort is warranted, as the ultimate benefit to patients is considerable.

Analysis of separate and combined effects of common variation in KCNJ11 and PPARG on risk of type 2 diabetes

The separate and combined effects of the PPARG Pro(12)Ala polymorphism and the KCNJ11 Glu(23)Lys polymorphisms on risk of type 2 diabetes were investigated in relatively large-scale, case-control studies. Separate effects of the variants were examined among 1187/1461 type 2 diabetic patients and 4791/4986 middle-aged, glucose-tolerant subjects. The combined analysis involved 1164 type 2 diabetic patients and 4733 middle-aged, glucose-tolerant subjects. In the separate analyses, the K allele of the KCNJ11 Glu(23)Lys associated with type 2 diabetes (odds ratio, 1.19; P = 0.0002), whereas the PPARG Pro(12)Ala showed no significant association with type 2 diabetes. The combined analysis indicated that the two polymorphisms acted in an additive manner to increase the risk of type 2 diabetes, and we found no evidence for a synergistic interaction between them. Analysis of a model with equal additive effects of the two variants showed that the odds ratio for type 2 diabetes increased with 1.14/risk allele (P = 0.003). Together, the two polymorphisms conferred a population-attributable risk for type 2 diabetes of 28%. In conclusion, our results showed no evidence of a synergistic interaction between the KCNJ11 Glu(23)Lys and PPARG Pro(12)Ala polymorphisms, but indicated that they may act in an additive manner to increase the risk of type 2 diabetes.