Alanine variant of the Pro12Ala polymorphism of the PPARgamma gene might be associated with decreased risk of diabetic retinopathy in type 2 diabetes

Association between the triglyceride glucose index and diabetic retinopathy in type 2 diabetes: a meta-analysis

The triglyceride-glucose (TyG) index is an accessible and reliable surrogate indicator of insulin resistance and is strongly associated with diabetes. However, its relationship with diabetic retinopathy (DR) remains controversial. This meta-analysis aimed to assess the relationship between the TyG index and the prevalence of DR. Initial studies were searched from PubMed, Embase, Web of Science, and China National Knowledge Infrastructure (CNKI) electronic databases. The retrieval time range was from the establishment of the database to June 2023. Pooled estimates were derived using a random-effects model and reported as odds ratio (OR) with 95% confidence intervals (CIs). Two researchers independently assessed the methodological quality of the included studies. The Newcastle-Ottawa Quality Scale (NOS) was utilized to assess cohort studies or case-control studies. The Agency for Healthcare Research and Quality (AHRQ) methodology checklist was applied to assess cross-sectional studies. Ten observational studies encompassing 13716 patients with type 2 diabetes were included in the meta-analysis. The results showed that a higher TyG index increased the risk of DR compared with a low TyG index (OR: 2.34, 95% CI: 1.31-4.19, P < 0.05). When the index was analyzed as a continuous variable, consistent results were observed (OR: 1.48, 95% CI: 1.12-1.97, P < 0.005). There was no significant effect on the results of the sensitivity analyses excluding one study at a time (P all < 0.05). A higher TyG index may be associated with an increased prevalence of DR in patients with type 2 diabetes. However, high-quality cohort or case-control studies are needed to further substantiate this evidence.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42023432747.

The Role of Genetic Polymorphisms in Diabetic Retinopathy: Narrative Review

Diabetic retinopathy (DR) is renowned as a leading cause of visual loss in working-age populations with its etiopathology influenced by the disturbance of biochemical metabolic pathways and genetic factors, including gene polymorphism. Metabolic pathways considered to have an impact on the development of the disease, as well as genes and polymorphisms that can affect the gene expression, modify the quantity and quality of the encoded product (protein), and significantly alter the metabolic pathway and its control, and thus cause changes in the functioning of metabolic pathways. In this article, the screening of chromosomes and the most important genes involved in the etiology of diabetic retinopathy is presented. The common databases with manuscripts published from January 2000 to June 2023 have been taken into consideration and chosen. This article indicates the role of specific genes in the development of diabetic retinopathy, as well as polymorphic changes within the indicated genes that may have an impact on exacerbating the symptoms of the disease. The collected data will allow for a broader look at the disease and help to select candidate genes that can become markers of the disease.

Association between PPAR-γ2 gene polymorphisms and diabetic retinopathy risk: a meta-analysis

A close association between peroxisome proliferator-activated receptor-γ2 (PPAR-γ2) and the development of diabetic retinopathy (DR) has been previously suggested. Herein, a meta-analysis was conducted to explore the association between PPAR-γ2 polymorphisms and DR risk by performing a systematic search and quantitative analysis. Overall, fourteen articles involving 10,527 subjects were included. The pooled results did not reveal an association between PPAR-γ2 rs1801282 C/G and DR susceptibility in the overall population (e.g., the dominant model: CG+GG vs. CC, OR=0.85, 95% CI=0.69-1.06, P=0.15, I²=62.9%). Furthermore, heterogeneity tests, cumulative analyses, sensitivity analyses, and publication bias analyses were conducted and showed that the results were robust. Similarly, race-based subgroup analyses and other subgroup analyses did not reveal an association between the rs1801282 C/G and DR susceptibility. In addition, no significant association was observed between PPAR-γ2 rs3856806 C/T polymorphism and DR risk (e.g., the dominant model: CT+TT vs. CC, OR=1.12, 95%CI=0.91-1.37, P=0.28, I²=27.0%). Overall, based on the current sample size and the level of evidence presented in the study, the results suggest that PPAR-γ2 gene polymorphisms are not associated with DR risk.

Leveraging Nuclear Receptors as Targets for Pathological Ocular Vascular Diseases

Vasculogenesis and angiogenesis are physiological mechanisms occurring throughout the body. Any disruption to the precise balance of blood vessel growth necessary to support healthy tissue, and the inhibition of abnormal vessel sprouting has the potential to negatively impact stages of development and/or healing. Therefore, the identification of key regulators of these vascular processes is critical to identifying therapeutic means by which to target vascular-associated compromises and complications. Nuclear receptors are a family of transcription factors that have been shown to be involved in modulating different aspects of vascular biology in many tissues systems. Most recently, the role of nuclear receptors in ocular biology and vasculopathies has garnered interest. Herein, we review studies that have used in vitro assays and in vivo models to investigate nuclear receptor-driven pathways in two ocular vascular diseases associated with blindness, wet or exudative age-related macular degeneration, and proliferative diabetic retinopathy. The potential therapeutic targeting of nuclear receptors for ocular diseases is also discussed.

Association of PTPN1 polymorphisms with breast cancer risk: A case-control study in Chinese females

BACKGROUND

Breast cancer (BC) risk, development, and prognosis were closely related to obesity, diabetes mellitus, and metabolic syndrome. Protein tyrosine phosphatase, non-receptor type 1 (PTPN1) located on chromosome 20q13, could negatively regulate insulin and leptin signaling. In this study, we determined the association of PTPN1 polymorphisms with BC risk.

METHODS

We analyzed the distribution of 11 selected PTPN1 single nucleotide polymorphisms in Chinese female patients with BC (n = 953) and healthy controls (n = 963) based on a multicenter case-control study. The association of PTPN1 genotypes and haplotypes frequencies with BC risk were determined by logistic regression analysis. Analyses were further stratified by body mass index (BMI), waist-hip rate (WHR), diabetes mellitus history, and fasting plasma glucose level. The eQTL (expression Quantitative Trait Loci) analysis for PTPN1 was conducted by GTEx database.

RESULTS

There were significant differences between BC cases and control groups in menopausal status, number of births, and BMI. Four single nucleotide polymorphisms (SNPs; rs3215684, rs3787345, rs718049, and rs718050) decreased overall BC risk, and other seven SNPs showed no significant association with BC risk. In multivariate analysis, BMI and rs3215684 DT + DD genotype were identified as independent risk factors for BC, and mutated genotypes of rs3215684 were correlated with increased PTPN1 expression. There are no haplotypes showed different frequencies between cases and controls. In the stratified analysis, rs2206656 showed a significant association with decreased BC risk in the subgroup of BMI ≤ 24 kg/m ² , while rs3215684 and rs718049 showed lower BC risk in the subgroup of WHR > 0.85. Seven SNPs showed lower BC risk in the subgroup with diabetes mellitus history and/or fasting plasma glucose level ≥ 7 mM, while rs754118 decreased BC risk in the subgroup of fasting plasma glucose level < 7 mM.

CONCLUSION

Our findings suggest that PTPN1 SNPs associated with BC susceptibility in Chinese females, which also suggested a novel mechanism between obesity, diabetes mellitus, and BC risk.

Diabetic macular oedema: under-represented in the genetic analysis of diabetic retinopathy

Diabetic retinopathy, a complication of both type 1 and type 2 diabetes, is a complex disease and is one of the leading causes of blindness in adults worldwide. It can be divided into distinct subclasses, one of which is diabetic macular oedema. Diabetic macular oedema can occur at any time in diabetic retinopathy and is the most common cause of vision loss in patients with type 2 diabetes. The purpose of this review is to summarize the large number of genetic association studies that have been performed in cohorts of patients with type 2 diabetes and published in English-language journals up to February 2017. Many of these studies have produced positive associations with gene polymorphisms and diabetic retinopathy. However, this review highlights that within this large body of work, studies specifically addressing a genetic association with diabetic macular oedema, although present, are vastly under-represented. We also highlight that many of the studies have small patient numbers and that meta-analyses often inappropriately combine patient data sets. We conclude that there will continue to be conflicting results and no meaningful findings will be achieved if the historical approach of combining all diabetic retinopathy disease states within patient cohorts continues in future studies. This review also identifies several genes that would be interesting to analyse in large, well-defined cohorts of patients with diabetic macular oedema in future candidate gene association studies.

Type 2 Diabetes Genetic Variants and Risk of Diabetic Retinopathy

PURPOSE

Genetic association studies to date have not identified any robust risk loci for diabetic retinopathy (DR). We hypothesized that individuals with more diabetes genetic risk alleles have a higher risk of developing DR.

DESIGN

Case-control genetic association study.

PARTICIPANTS

We evaluated the aggregate effects of multiple type 2 diabetes-associated genetic variants on the risk of DR among 1528 participants with diabetes from the Singapore Epidemiology of Eye Diseases Study, of whom 547 (35.8%) had DR.

METHODS

Participants underwent a comprehensive ocular examination, including dilated fundus photography. Retinal photographs were graded using the modified Airlie House classification system to assess the presence and severity of DR following a standardized protocol. We identified 76 previously discovered type 2 diabetes-associated single nucleotide polymorphisms (SNPs) and constructed multilocus genetic risk scores (GRSs) for each individual by summing the number of risk alleles for each SNP weighted by the respective effect estimates on DR. Two GRSs were generated: an overall GRS that included all 76 discovered type 2 diabetes-associated SNPs, and an Asian-specific GRS that included a subset of 55 SNPs previously found to be associated with type 2 diabetes in East and/or South Asian ancestry populations. Associations between the GRSs with DR were determined using logistic regression analyses. Discriminating ability of the GRSs was determined by the area under the receiver operating characteristic curve (AUC).

MAIN OUTCOME MEASURES

Odds ratios on DR.

RESULTS

Participants in the top tertile of the overall GRS were 2.56-fold more likely to have DR compared with participants in the lowest tertile. Participants in the top tertile of the Asian-specific GRS were 2.00-fold more likely to have DR compared with participants in the bottom tertile. Both GRSs were associated with higher DR severity levels. However, addition of the GRSs to traditional risk factors improved the AUC only modestly by 3% to 4%.

CONCLUSIONS

Type 2 diabetes-associated genetic loci were significantly associated with higher risks of DR, independent of traditional risk factors. Our findings may provide new insights to further our understanding of the genetic pathogenesis of DR.

Association analysis of PPARγ (p.Pro12Ala) polymorphism with type 2 diabetic retinopathy in patients from north India

BACKGROUND

The present study aimed to examine the association of PPARγ (p.Pro12Ala) polymorphism with type 2 diabetic retinopathy (DR) in patients from north India.

MATERIAL AND METHODS

In this case-control association study a total of 1325 subjects (717 DR patients and 608 individuals with confirmed type 2 diabetes mellitus (T2DM) without retinopathy taken as controls (CDR)), were recruited. Genotyping for PPARγ (p.Pro12Ala) polymorphism was performed by Taqman SNP Genotyping Assays using Real time PCR.

RESULTS

Statistically significant differences were observed between the two analyzed groups in the duration of diabetes and random blood glucose levels (p = 0.000 and p = 0.011, respectively). However, genotype and allele frequency distribution of PPARγ (p.Pro12Ala) polymorphism did not differ significantly between DR and CDR groups (p = 0.507 and 0.625, respectively).

CONCLUSIONS

These findings suggest no significant association of p.Pro12Ala polymorphism with retinopathy in tested type 2 diabetic retinopathy patients as compared to T2DM individuals take as controls. To our knowledge, this is the first report of association analysis of p.Pro12Ala polymorphism in PPARγ in DR patients from India.

The gene polymorphisms of UCP1 but not PPAR γ and TCF7L2 are associated with diabetic retinopathy in Chinese type 2 diabetes mellitus cases

PURPOSE

This study was designed to investigate the association between the polymorphisms in three insulin resistance-related genes, uncoupling protein-1 (UCP1), peroxisome proliferator-activated receptor γ (PPARγ) and transcription factor 7-like 2 (TCF7L2) and the susceptibility to diabetic retinopathy (DR) in a Chinese type 2 diabetes mellitus (T2DM) cohort.

METHODS

A total of 792 patients with T2DM were enrolled and categorized into two groups: (1) the DR group consisted of 448 patients, which was further subclassified into a proliferative DR (PDR) group with 220 patients and a non-proliferative DR (NPDR) group with 228 patients; (2) the diabetes without retinopathy (DNR) group, comprised 344 patients who had no signs of DR. Single-nucleotide polymorphisms (SNPs), rs1800592 in the UCP1 gene, rs1801282, rs3856806 and rs1249719 in the PPARγ gene and rs11196205 in the TCF7L2 gene were genotyped in this study.

RESULTS

For SNP rs1800592 of the UCP1 gene, the frequency of allele G and genotype GG was significantly higher in the PDR group than in the DNR group (allele OR: 1.32, 95% CI: 1.03-1.68, p = 0.03; genotype OR: 1.72, 95%CI: 1.06-2.79, p = 0.03). No evident association was found between the allele frequencies and genotype distributions of any individual SNP in the PPARγ or TCF7L2 genes and DR, PDR or NPDR. Haplotype analyses of the PPARγ gene did not provide any evidence for an association with DR, PDR or NPDR in this Chinese T2DM cohort.

CONCLUSIONS

This study suggests that the SNP rs1800592 in the UCP1 gene is associated with increased risk of PDR in the Chinese T2DM population.

Human genetics of diabetic retinopathy

There is evidence demonstrating that genetic factors contribute to the risk of diabetic retinopathy (DR). Genetics variants, structural variants (copy number variation, CNV) and epigenetic changes play important roles in the development of DR. Genetic linkage and association studies have uncovered a number of genetic loci and common genetic variants susceptibility to DR. CNV and interactions of gene by environment have also been detected by association analysis. Apart from nucleus genome, mitochondrial DNA plays critical roles in regulation of development of DR. Epigenetic studies have indicated epigenetic changes in chromatin affecting gene transcription in response to environmental stimuli, which provided a large body of evidence of regulating development of diabetes mellitus. Identification of genetic variants and epigenetic changes contributed to risk or protection of DR will benefit uncovering the complex mechanism underlying DR. This review focused on the current knowledge of the genetic and epigenetic basis of DR.

Association of monocyte chemoattractant protein-1 (MCP-1) 2518A/G polymorphism with proliferative diabetic retinopathy in Korean type 2 diabetes

PURPOSE

Monocyte chemoattractant protein-1 (MCP-1) is a chemokine that can increase adhesion molecule expression on monocytes and produce superoxide anions. Hyperglycemia induces MCP-1 production in vascular endothelial cells and retinal pigmented epithelial cells, and has been implicated as a causal factor in the facilitation of vascular complications in diabetes. In the present study, we evaluated the association of a single nucleotide polymorphism (SNP) in the MCP-1 gene with proliferative diabetic retinopathy (PDR) in a Korean population with type 2 diabetes.

MATERIALS AND METHODS

We conducted a case-control study, which enrolled 590 subjects with type 2 diabetes, and SNP genotyping of c.2518A/G in the MCP-1 gene was performed using polymerase chain reaction followed by digestion with PvuII restriction enzyme.

RESULTS

The prevalence of c.2518A/G polymorphism in diabetic patients was 13.2% (A/A), 47.1% (A/G) and 39.7% (G/G). In patients with diabetic retinopathy, the prevalence of PDR was significantly higher (p=0.009) in diabetic subjects with the c.2518A/A genotype (35.9%; n=78) compared to those with either the A/G or G/G genotype (22.3%, n=512). The prevalence of any other micro and macro-complications, including nephropathy and cerebrovascular events, were not different according to the c.2518A/G genotype.

CONCLUSION

Our new genetic findings suggest that the c.2518A/A genotype in MCP-1 could be used as a susceptibility gene to predispose Koreans exhibiting type 2 diabetes for the development of PDR.

Is PPARG the key gene in diabetic retinopathy?

Diabetic retinopathy, a microvascular complication of diabetes mellitus, is major cause of non-inherited blindness among adults. Although diabetic retinopathy is a common complication of diabetes, we still know little about the underlying molecular mechanisms. In recent years, complex connections between important molecules and pathways in the onset and progression of diabetic retinopathy, such as advanced glycation end products, oxidative stress and inflammation, have been elucidated. Biochemical, genetic and functional studies strongly indicate peroxisome proliferator-activated receptor-γ (PPARγ), a pleiotropic transcription factor, as a primary target in the treatment of diabetic retinopathy. In this issue, Song et al. detail the role of PPARγ in diabetic retinopathy-related disorders, illustrating PPARγ-mediated inhibition of diabetes-induced leukostasis and leakage, and its beneficial role in modulating inflammation, angiogenesis and apoptosis in retinal and endothelial cells. Moreover, they describe alternative treatments for diabetic retinopathy, such as plant-derived PPARγ ligands, proposing their use - in combination with standard therapies - for modulation of diabetic retinopathy.

Development of novel drugs for ocular diseases: possibilities for individualized therapy

In clinical ophthalmology, new and old drug regimens are available for the treatment of major eye diseases, including potentially blinding conditions, such as glaucoma, and various macular diseases. In glaucoma, therapeutic treatment mainly deals with control of intraocular pressure at low levels but the clinical courses of patients can be very variable. Very often, specific drug combinations and dosages have to be formulated for individual glaucoma patients. In neovascular age-related macular degeneration, choroidal neovascularization can lead to progressive and irreversible visual impairment if not treated early. In recent years, clinical trials using photodynamic therapy with verteporfin and various anti-VEGF antibodies, such as ranibizumab and bevacizumab, have enhanced the treatment outcomes of neovascular age-related macular degeneration. In diabetic macular edema, intravitreal triamcinolone acetonide and anti-VEGF therapy are effective in some patients. Again, responses to treatment are not uniform in all macular patients. Traditional herbal medicine has long been known to play a role in the practice of personalized formulations in Asia. Potential preventive and therapeutic effects have been claimed in individual eye patients. Meanwhile, advanced technologies in molecular biology have led to identification of genes associated with many eye diseases and development of the concept of individual medicine, in which the genotype of a person can be used as a basis for disease prediction or prophylactic treatments. Moreover, pharmacogenomic studies have demonstrated the association of various genotypes or haplotypes with responses to drug therapies, providing hope for tailormade personalized treatments. The combination of genotypic information with clinical features for the prescription of treatment modes in eye diseases is under vigorous research.

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.