FHL2 Genetic Polymorphisms and Pro-Diabetogenic Lipid Profile in the Multiethnic HELIUS Cohort.

Type 2 diabetes mellitus (T2D) is a prevalent disease often accompanied by the occurrence of dyslipidemia. Four and a half LIM domains 2 (FHL2) is a scaffolding protein, whose involvement in metabolic disease has recently been demonstrated. The association of human FHL2 with T2D and dyslipidemia in a multiethnic setting is unknown. Therefore, we used the large multiethnic Amsterdam-based Healthy Life in an Urban Setting (HELIUS) cohort to investigate FHL2 genetic loci and their potential role in T2D and dyslipidemia. Baseline data of 10,056 participants from the HELIUS study were available for analysis. The HELIUS study contained individuals of European Dutch, South Asian Surinamese, African Surinamese, Ghanaian, Turkish, and Moroccan descent living in Amsterdam and were randomly sampled from the municipality register. Nineteen FHL2 polymorphisms were genotyped, and associations with lipid panels and T2D status were investigated. We observed that seven FHL2 polymorphisms associated nominally with a pro-diabetogenic lipid profile including triglyceride (TG), high-density and low-density lipoprotein-cholesterol (HDL-C and LDL-C), and total cholesterol (TC) concentrations, but not with blood glucose concentrations or T2D status in the complete HELIUS cohort upon correcting for age, gender, BMI, and ancestry. Upon stratifying for ethnicity, we observed that only two of the nominally significant associations passed multiple testing adjustments, namely, the association of rs4640402 with increased TG and rs880427 with decreased HDL-C concentrations in the Ghanaian population. Our results highlight the effect of ethnicity on pro-diabetogenic selected lipid biomarkers within the HELIUS cohort, as well as the need for more large multiethnic cohort studies.

Early adipogenesis is repressed through the newly identified FHL2-NFAT5 signaling complex.

The LIM-domain-only protein FHL2 is a modulator of signal transduction and has been shown to direct the differentiation of mesenchymal stem cells towards osteoblast and myocyte phenotypes. We hypothesized that FHL2 may simultaneously interfere with the induction of the adipocyte lineage. Therefore, we investigated the role of FHL2 in adipocyte differentiation. For these studies pre-adipocytes isolated from mouse adipose tissue and the 3T3-L1 (pre)adipocyte cell line were applied. We performed FHL2 gain of function and knockdown experiments followed by extensive RNAseq analyses and phenotypic characterization of the cells by oil-red O (ORO) lipid staining. Through affinity-purification mass spectrometry (AP-MS) novel FHL2 interacting proteins were identified. Here we report that FHL2 is expressed in pre-adipocytes and for accurate adipocyte differentiation, this protein needs to be downregulated during the early stages of adipogenesis. More specifically, constitutive overexpression of FHL2 drastically inhibits adipocyte differentiation in 3T3-L1 cells, which was demonstrated by suppressed activation of the adipogenic gene expression program as shown by RNAseq analyses, and diminished lipid accumulation. Analysis of the protein-protein interactions mediating this repressive activity of FHL2 on adipogenesis revealed the interaction of FHL2 with the Nuclear factor of activated T-cells 5 (NFAT5). NFAT5 is an established inhibitor of adipocyte differentiation and its knockdown rescued the inhibitory effect of FHL2 overexpression on 3T3-L1 differentiation, indicating that these proteins act cooperatively. We present a new regulatory function of FHL2 in early adipocyte differentiation and revealed that FHL2-mediated inhibition of pre-adipocyte differentiation is dependent on its interaction with NFAT5. FHL2 expression increases with aging, which may affect mesenchymal stem cell differentiation, more specifically inhibit adipocyte differentiation.

Glucose-mediated insulin secretion is improved in FHL2-deficient mice and elevated FHL2 expression in humans is associated with type 2 diabetes.

AIMS/HYPOTHESIS: The general population is ageing, involving an enhanced incidence of chronic diseases such as type 2 diabetes. With ageing, DNA methylation of FHL2 increases, as well as expression of the four and a half LIM domains 2 (FHL2) protein in human pancreatic islets. We hypothesised that FHL2 is actively involved in glucose metabolism. METHODS: Publicly available microarray datasets from human pancreatic islets were analysed for FHL2 expression. In FHL2-deficient mice, we studied glucose clearance and insulin secretion. Gene expression analysis and glucose-stimulated insulin secretion (GSIS) were determined in isolated murine FHL2-deficient islets to evaluate insulin-secretory capacity. Moreover, knockdown and overexpression of FHL2 were accomplished in MIN6 cells to delineate the underlying mechanism of FHL2 function. RESULTS: Transcriptomics of human pancreatic islets revealed that individuals with elevated levels of HbA1c displayed increased FHL2 expression, which correlated negatively with insulin secretion pathways. In line with this observation, FHL2-deficient mice cleared glucose more efficiently than wild-type littermates through increased plasma insulin levels. Insulin sensitivity was comparable between these genotypes. Interestingly, pancreatic islets isolated from FHL2-deficient mice secreted more insulin in GSIS assays than wild-type mouse islets even though insulin content and islet size was similar. To support this observation, we demonstrated increased expression of the transcription factor crucial in insulin secretion, MAF BZIP transcription factor A (MafA), higher expression of GLUT2 and reduced expression of the adverse factor c-Jun in FHL2-deficient islets. The underlying mechanism of FHL2 was further delineated in MIN6 cells. FHL2-knockdown led to enhanced activation of forkhead box protein O1 (FOXO1) and its downstream genes such as Mafa and Pdx1 (encoding pancreatic and duodenal homeobox 1), as well as increased glucose uptake. On the other hand, FHL2 overexpression in MIN6 cells blocked GSIS, increased the formation of reactive oxygen species and increased c-Jun activity. CONCLUSIONS/INTERPRETATION: Our data demonstrate that FHL2 deficiency improves insulin secretion from beta cells and improves glucose tolerance in mice. Given that FHL2 expression in humans increases with age and that high expression levels of FHL2 are associated with beta cell dysfunction, we propose that enhanced FHL2 expression in elderly individuals contributes to glucose intolerance and the development of type 2 diabetes. DATA AVAILABILITY: The human islet microarray datasets used are publicly available and can be found on https://www.ncbi.nlm.nih.gov/geo/ .

How (Epi)Genetic Regulation of the LIM-Domain Protein FHL2 Impacts Multifactorial Disease.

Susceptibility to complex pathological conditions such as obesity, type 2 diabetes and cardiovascular disease is highly variable among individuals and arises from specific changes in gene expression in combination with external factors. The regulation of gene expression is determined by genetic variation (SNPs) and epigenetic marks that are influenced by environmental factors. Aging is a major risk factor for many multifactorial diseases and is increasingly associated with changes in DNA methylation, leading to differences in gene expression. Four and a half LIM domains 2 (FHL2) is a key regulator of intracellular signal transduction pathways and the FHL2 gene is consistently found as one of the top hyper-methylated genes upon aging. Remarkably, FHL2 expression increases with methylation. This was demonstrated in relevant metabolic tissues: white adipose tissue, pancreatic ß-cells, and skeletal muscle. In this review, we provide an overview of the current knowledge on regulation of FHL2 by genetic variation and epigenetic DNA modification, and the potential consequences for age-related complex multifactorial diseases.

Four-and-a-half LIM domain protein 2 (FHL2) deficiency protects mice from diet-induced obesity and high FHL2 expression marks human obesity.

OBJECTIVE: Four-and-a-Half-LIM-domain-protein 2 (FHL2) modulates multiple signal transduction pathways but has not been implicated in obesity or energy metabolism. In humans, methylation and expression of the FHL2 gene increases with age, and high FHL2 expression is associated with increased body weight in humans and mice. This led us to hypothesize that FHL2 is a determinant of diet-induced obesity. METHODS: FHL2-deficient (FHL2-/-) and wild type male mice were fed a high-fat diet. Metabolic phenotyping of these mice, as well as transcriptional analysis of key metabolic tissues was performed. Correlation of the expression of FHL2 and relevant genes was assessed in datasets from white adipose tissue of individuals with and without obesity. RESULTS: FHL2 Deficiency protects mice from high-fat diet-induced weight gain, whereas glucose handling is normal. We observed enhanced energy expenditure, which may be explained by a combination of changes in multiple tissues; mild activation of brown adipose tissue with increased fatty acid uptake, increased cardiac glucose uptake and browning of white adipose tissue. Corroborating our findings in mice, expression of FHL2 in human white adipose tissue positively correlates with obesity and negatively with expression of browning-associated genes. CONCLUSION: Our results position FHL2 as a novel regulator of obesity and energy expenditure in mice and human. Given that FHL2 expression increases during aging, we now show that low FHL2 expression associates with a healthy metabolic state.