Distinct regulation of hepatic nuclear factor 1alpha by NKX6.1 in pancreatic beta cells

MODY Only Monogenic? A Narrative Review of the Novel Rare and Low-Penetrant Variants

Maturity-onset diabetes of the young (MODY) represents the most frequent form of monogenic diabetes mellitus (DM), currently classified in 14 distinct subtypes according to single gene mutations involved in the differentiation and function of pancreatic β-cells. A significant proportion of MODY has unknown etiology, suggesting that the genetic landscape is still to be explored. Recently, novel potentially MODY-causal genes, involved in the differentiation and function of β-cells, have been identified, such as RFX6, NKX2.2, NKX6.1, WFS1, PCBD1, MTOR, TBC1D4, CACNA1E, MNX1, AKT2, NEUROG3, EIF2AK3, GLIS3, HADH, and PTF1A. Genetic and clinical features of MODY variants remain highly heterogeneous, with no direct genotype-phenotype correlation, especially in the low-penetrant subtypes. This is a narrative review of the literature aimed at describing the current state-of-the-art of the novel likely MODY-associated variants. For a deeper understanding of MODY complexity, we also report some related controversies concerning the etiological role of some of the well-known pathological genes and MODY inheritance pattern, as well as the rare association of MODY with autoimmune diabetes. Due to the limited data available, the assessment of MODY-related genes pathogenicity remains challenging, especially in the setting of rare and low-penetrant subtypes. In consideration of the crucial importance of an accurate diagnosis, prognosis and management of MODY, more studies are warranted to further investigate its genetic landscape and the genotype-phenotype correlation, as well as the pathogenetic contribution of the nongenetic modifiers in this cohort of patients.

Deficiency of transcription factor Nkx6.1 does not prevent insulin secretion in INS-1E cells

Pancreatic-β-cell-specifying transcription factor Nkx6.1, indispensable for embryonic development of the pancreatic epithelium and commitment to β-cell lineage, directly controls the expression of a glucose transporter (Glut2), pyruvate carboxylase (Pcx), and genes for insulin processing (endoplasmic reticulum oxidoreductase-1β, Ero1lb; zinc transporter-8, Slc30a8). The Nkx6.1 decline in aging diabetic Goto-Kakizaki rats contributes to β-cell trans-differentiation into δ-cells. Elucidating further Nkx6.1 roles, we studied Nkx6.1 ablation in rat INS-1E cells, prepared by CRISPR/Cas9 gene editing from single colonies. INS-1E^Nkx6.1-/- cells exhibited unchanged glucose-stimulated insulin secretion (GSIS), moderately decreased phosphorylating/non-phosphorylating respiration ratios at high glucose; unchanged but delayed ATP-elevation responses to glucose; delayed uptake of fluorescent glucose analog, but slightly improved cytosolic Ca²⁺-oscillations, induced by glucose; despite approximately halved Glut2, Pcx, Ero1lb, and Slc30a8 expression, and reduced nuclear receptors Nr4a1 and Nr4a3. Thus, ATP synthesis was time-compensated, despite the delayed GLUT2-mediated glucose uptake and crippled pyruvate-malate redox shuttle (owing to the PCX-deficiency) in INS-1E^Nkx6.1-/- cells. Nkx6.1 thus controls the expression of genes that are not essential for acute insulin secretion, the function of which can be compensated for. Considerations that Nkx6.1 deficiency is an ultimate determinant of β-cell pathology beyond cell trans-(de-)differentiation or β-cell identity are not supported by our results.

HNF1A：From Monogenic Diabetes to Type 2 Diabetes and Gestational Diabetes Mellitus

Diabetes, a disease characterized by hyperglycemia, has a serious impact on the lives and families of patients as well as on society. Diabetes is a group of highly heterogeneous metabolic diseases that can be classified as type 1 diabetes (T1D), type 2 diabetes (T2D), gestational diabetes mellitus (GDM), or other according to the etiology. The clinical manifestations are more or less similar among the different types of diabetes, and each type is highly heterogeneous due to different pathogenic factors. Therefore, distinguishing between various types of diabetes and defining their subtypes are major challenges hindering the precise treatment of the disease. T2D is the main type of diabetes in humans as well as the most heterogeneous. Fortunately, some studies have shown that variants of certain genes involved in monogenic diabetes also increase the risk of T2D. We hope this finding will enable breakthroughs regarding the pathogenesis of T2D and facilitate personalized treatment of the disease by exploring the function of the signal genes involved. Hepatocyte nuclear factor 1 homeobox A (HNF1α) is widely expressed in pancreatic β cells, the liver, the intestines, and other organs. HNF1α is highly polymorphic, but lacks a mutation hot spot. Mutations can be found at any site of the gene. Some single nucleotide polymorphisms (SNPs) cause maturity-onset diabetes of the young type 3 (MODY3) while some others do not cause MODY3 but increase the susceptibility to T2D or GDM. The phenotypes of MODY3 caused by different SNPs also differ. MODY3 is among the most common types of MODY, which is a form of monogenic diabetes mellitus caused by a single gene mutation. Both T2D and GDM are multifactorial diseases caused by both genetic and environmental factors. Different types of diabetes mellitus have different clinical phenotypes and treatments. This review focuses on HNF1α gene polymorphisms, HNF1A-MODY3, HNF1A-associated T2D and GDM, and the related pathogenesis and treatment methods. We hope this review will provide a valuable reference for the precise and individualized treatment of diabetes caused by abnormal HNF1α by summarizing the clinical heterogeneity of blood glucose abnormalities caused by HNF1α mutation.

NKX6.1 transcription factor: a crucial regulator of pancreatic β cell development, identity, and proliferation

Understanding the biology underlying the mechanisms and pathways regulating pancreatic β cell development is necessary to understand the pathology of diabetes mellitus (DM), which is characterized by the progressive reduction in insulin-producing β cell mass. Pluripotent stem cells (PSCs) can potentially offer an unlimited supply of functional β cells for cellular therapy and disease modeling of DM. Homeobox protein NKX6.1 is a transcription factor (TF) that plays a critical role in pancreatic β cell function and proliferation. In human pancreatic islet, NKX6.1 expression is exclusive to β cells and is undetectable in other islet cells. Several reports showed that activation of NKX6.1 in PSC-derived pancreatic progenitors (MPCs), expressing PDX1 (PDX1⁺/NKX6.1⁺), warrants their future commitment to monohormonal β cells. However, further differentiation of MPCs lacking NKX6.1 expression (PDX1⁺/NKX6.1⁻) results in an undesirable generation of non-functional polyhormonal β cells. The importance of NKX6.1 as a crucial regulator in MPC specification into functional β cells directs attentions to further investigating its mechanism and enhancing NKX6.1 expression as a means to increase β cell function and mass. Here, we shed light on the role of NKX6.1 during pancreatic β cell development and in directing the MPCs to functional monohormonal lineage. Furthermore, we address the transcriptional mechanisms and targets of NKX6.1 as well as its association with diabetes.

HNF1A variant, energy-reduced diets and insulin resistance improvement during weight loss: The POUNDS Lost trial and DIRECT

AIM

To determine whether weight-loss diets varying in macronutrients modulate the genetic effect of hepatocyte nuclear factor 1α (HNF1A) rs7957197 on weight loss and improvement of insulin resistance.

MATERIALS AND METHODS

We analysed the interaction between HNF1A rs7957197 and weight-loss diets with regard to weight loss and insulin resistance improvement among 722 overweight/obese adults from a 2-year randomized weight-loss trial, the POUNDS Lost trial. The findings were replicated in another independent 2-year weight-loss trial, the Dietary Intervention Randomized Controlled Trial (DIRECT), in 280 overweight/obese adults.

RESULTS

In the POUNDS Lost trial, we found that a high-fat diet significantly modified the genetic effect of HNF1A on weight loss and reduction in waist circumference (P for interaction = .006 and .005, respectively). Borderline significant interactions for fasting insulin and insulin resistance (P for interaction = .07 and .06, respectively) were observed. We replicated the results in DIRECT. Pooled results showed similar significant interactions with weight loss, waist circumference reduction, and improvement in fasting insulin and insulin resistance (P values for interaction = .001, .005, .02 and .03, respectively). Greater decreases in weight, waist circumference, fasting insulin level and insulin resistance were observed in participants with the T allele compared to those without the T allele in the high-fat diet group (P = .04, .03 and .01, respectively).

CONCLUSIONS

Our replicable findings provide strong evidence that individuals with the HNF1A rs7957197 T allele might obtain more benefits in weight loss and improvement of insulin resistance by choosing a hypocaloric and high-fat diet.

NKX6.1 functions as a metastatic suppressor through epigenetic regulation of the epithelial-mesenchymal transition

The transcription factor NKX6.1 (NK6 homeobox 1) is important in the development of pancreatic β-cells and neurons. Although recent publications show that NKX6.1 is hypermethylated and downregulated during tumorigenesis, the function of NKX6.1 in carcinogenesis remains elusive. Here, we address the metastasis suppressor function of human NKX6.1 using cell, animal and clinical analyses. Our data show that NKX6.1 represses tumor formation and metastatic ability both in vitro and in vivo. Mechanistically, NKX6.1 suppresses cell invasion by inhibiting the epithelial-to-mesenchymal transition (EMT). NKX6.1 directly enhances the mRNA level of E-cadherin by recruiting BAF155 coactivator and represses that of vimentin and N-cadherin by recruiting RBBP7 (retinoblastoma binding protein 7) corepressor. Clinical cancer tumors with metastasis show low NKX6.1 protein expression coinciding with low E-cadherin and high vimentin expression. Our results demonstrate that NKX6.1 functions as an EMT suppressor by interacting with different epigenetic modifiers, making it a potential novel therapeutic option.

Pancreatic and duodenal homeobox gene 1 (Pdx1) down-regulates hepatic transcription factor 1 alpha (HNF1α) expression during reprogramming of human hepatic cells into insulin-producing cells

Ectopic expression of Pdx1 triggers rapid hepatocyte dedifferentiation by down-regulating liver-enriched transcription factors and liver-specific functional genes such as hepatic nuclear factor-1α (HNF1α), albumin, and AAT. However, the links between Pdx1 over-expression and hepatic gene down-regulation are incompletely understood. HNF1α and HNF4α are important transcription factors that establish and maintain the hepatocyte phenotype. The human HNF4α gene contains two promoters (P1 and P2) that drive expression of P1-(HNF4α 1-6) or P2-(HNF4α 7-9)-derived isoforms, which are used in different tissues and at different times during development. We hypothesized that the relative expression of HNF1α and HNF4α following ectopic Pdx1 expression may promote hepatic cell dedifferentiation and transdifferentiation toward pancreatic beta-cells. We produced lentiviruses expressing Pdx1, Pdx1-VP16, and Ngn3, along with dual-color reporter genes to indicate hepatic and pancreatic beta-cell phenotype changes. Using these PTF alone or in combinations, we demonstrated that Pdx1 not only activates specific beta-cell genes but down-regulates HNF1α. Pdx1-mediated reduction of HNF1α is accompanied by altered expression of its major activator, HNF4α isoforms, down-regulating hepatic genes ALB and AAT. Pdx1 up-regulates HNF4α via the P2 promoter. These P2-driven isoforms compete with P1-driven isoforms to suppress target gene transcription. In Huh7 cells, the AF-1 activation domain is more important for transactivation, whereas in INS1 cells, the F inhibitory domain is more important. The loss and gain of functional activity strongly suggests that Pdx1 plays a central role in reprogramming hepatocytes into beta-cells by suppressing the hepatic phenotype.

Exploring the role of the HNF-1αG319S polymorphism in β cell failure and youth-onset type 2 diabetes: Lessons from MODY and Hnf-1α-deficient animal models

The prevalence of youth-onset type 2 diabetes (T2D) is rapidly increasing worldwide, disproportionately affecting Indigenous youth with Oji-Cree heritage from central Canada. Candidate gene screening has uncovered a novel and private polymorphism in the Oji-Cree population in the hepatocyte nuclear factor-1 alpha (HNF-1α) gene, where a highly conserved glycine residue at position 319 is changed to a serine (termed HNF-1αG319S or simply G319S). Oji-Cree youth who carry one or two copies of the "S-allele" present at diagnosis with less obesity, reduced indicators of insulin resistance, and lower plasma insulin levels at diagnosis, suggestive of a primary defect in the insulin-secreting β cells. Few studies on the impact of the HNF-1αG319S variant on β cell function have been performed to date; however, much can be learned from other clinical phenotypes of HNF-1α-deficiency, including HNF-1α mutations that cause maturity-onset diabetes of the young 3 (MODY3). In addition, evaluation of Hnf-1α-deficient murine models reveals that HNF-1α plays a central role in the regulation of insulin secretion by regulating the expression of key genes involved in β cell glucose-sensing, mitochondrial function, and the maintenance of the β cell phenotype in differentiated β cells. The overall goal of this minireview is to explore the impact of HNF-1α-deficiency on the β cell to better inform future research into the mechanisms of β cell dysfunction in Oji-Cree youth with T2D.

Pharmacogenomics of anti-platelet therapy focused on peripheral blood cells of coronary arterial disease patients

BACKGROUND

To investigate genes differentially expressed in peripheral blood cells (PBCs) from patients with coronary arterial disease (CAD) under double anti-platelet therapy.

METHODS

Twenty-six CAD patients that were submitted to percutaneous coronary intervention (PCI) were selected to participate in this study. These patients took 100mg/day of acetylsalicylic acid (ASA) and 75mg/day of clopidogrel. Blood samples were collected before PCI to evaluate platelet reactivity using VerifyNow ASA and P2Y12 assays (Accumetrics). The patients were stratified into 4 quartiles based on ASA reaction units (ARUs) and P2Y12 reaction units (PRUs). Quartile 1 (Q1) patients were classified as responders and quartile 4 (Q4) patients as non-responders. Global mRNA expression from Q1 to Q4 was analyzed by microarray using the GeneChip Exon 1.0 ST array (Affymetrix) and was confirmed by RT-qPCR.

RESULTS

Patients with ARU or PRU values within the first quartile (Q1, ARU<390 and PRU<151) were considered responders, while those who had ARU or PRU within the fourth quartile (Q4, ARU>467 and PRU>260) were considered nonresponders. The risk factors associated for CAD showed expected frequencies and no difference was found between Q1 and Q4. Microarray analysis identified 117 genes differentially expressed for ASA and 29 for clopidogrel between Q1 and Q4 groups (p<0.01, FC>1.2).

CONCLUSION

The variation in response to ASA may be related with an increased expression of IGF1 and IGF1R, as well as a response to clopidogrel can be affected by pharmacokinetic change related to the reverse transport pathway by increased expression of ABCC3.

Prioritization of biomarker targets in human umbilical cord blood: identification of proteins in infant blood serving as validated biomarkers in adults

BACKGROUND

Early diagnosis represents one of the best lines of defense in the fight against a wide array of human diseases. Umbilical cord blood (UCB) is one of the first easily available diagnostic biofluids and can inform about the health status of newborns. However, compared with adult blood, its diagnostic potential remains largely untapped.

OBJECTIVES

Our goal was to accelerate biomarker research on UCB by exploring its detectable protein content and providing a priority list of potential biomarkers based on known proteins involved in disease pathways.

METHODS

We explored cord blood serum proteins by profiling a UCB pool of 12 neonates with different backgrounds using a combination of isoelectric focusing and liquid chromatography coupled with matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) and by comparing results with information contained in metabolic and disease databases available for adult blood.

RESULTS

A total of 1,210 UCB proteins were identified with a protein-level false discovery rate of ~ 5% as estimated by naïve target-decoy and MAYU approaches, signifying a 6-fold increase in the number of UCB proteins described to date. Identified proteins correspond to 138 different metabolic and disease pathways and provide a platform of mechanistically linked biomarker candidates for tracking disruptions in cellular processes. Moreover, among the identified proteins, 38 were found to be approved biomarkers for adult blood.

CONCLUSIONS

The results of this study advance current knowledge of the human cord blood serum proteome. They showcase the potential of UCB as a diagnostic medium for assessing infant health by detection and identification of candidate biomarkers for known disease pathways using a global, nontargeted approach. These biomarkers may inform about mechanisms of exposure-disease relationships. Furthermore, biomarkers approved by the U.S. Food and Drug Administration for screening in adult blood were detected in UCB and represent high-priority targets for immediate validation.