Search

The transcription factor NFATC2 induces [beta] cell proliferation in mouse and human islets. However, the genomic targets that mediate these effects have not been identified. We expressed active forms of Nfatc2 and Nfatcl in human islets. By integrating changes in gene expression with genomic binding sites for NFATC2, we identified approximately 2200 transcriptional targets of NFATC2. Genes induced by NFATC2 were enriched for transcripts that regulate the cell cycle and for DNA motifs associated with the transcription factor FOXP. Islets from an endocrine-specific Foxpl, Foxp2, and Foxp4 triple-knockout mouse were less responsive to NFATC2-induced [beta] cell proliferation, suggesting the FOXP family works to regulate [beta] cell proliferation in concert with NFATC2. NFATC2 induced [beta] cell proliferation in both mouse and human islets, whereas NFATC1 did so only in human islets. Exploiting this species difference, we identified approximately 250 direct transcriptional targets of NFAT in human islets. This gene set enriches for cell cycle- associated transcripts and includes Nr4a1. Deletion of Nr4a1 reduced the capacity of NFATC2 to induce [beta] cell proliferation, suggesting that much of the effect of NFATC2 occurs through its induction of Nr4a1. Integration of noncoding RNA expression, chromatin accessibility, and NFATC2 binding sites enabled us to identify NFATC2-dependent enhancer loci that mediate [beta] cell proliferation., Introduction Genetic association and linkage studies are designed to investigate the relationship between genetic variation at a gene locus and phenotypes, including those with disease relevance. GWAS in humans have [...]

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease in the U.S. and has a significant impact on human suffering. Leptin-deficient BTBR (BTBRob/ob) mice develop hallmark features of obesity-induced DN, whereas leptin-deficient C57BL/6J (B6ob/ob) mice do not. To identify genetic loci that underlie this strain difference, we constructed an F2 intercross between BTBRob/ob and B6ob/ob mice. We isolated kidneys from 460 F2 mice and histologically scored them for percent mesangial matrix and glomerular volume (∼50 glomeruli per mouse), yielding ∼45,000 distinct measures in total. The same histological measurements were made in kidneys from B6 and BTBR mice, either lean or obese (Lepob/ob), at 4 and 10 weeks of age, allowing us to assess the contribution of strain, age, and obesity to glomerular pathology. All F2 mice were genotyped for ∼5,000 single nucleotide polymorphisms (SNPs), ∼2,000 of which were polymorphic between B6 and BTBR, enabling us to identify a quantitative trait locus (QTL) on chromosome 7, with a peak at ∼30 Mbp, for percent mesangial matrix, glomerular volume, and mesangial volume. The podocyte-specific gene nephrin (Nphs1) is physically located at the QTL and contains high-impact SNPs in BTBR, including several missense variants within the extracellular immunoglobulin-like domains. Article Highlights: Diabetes is the leading cause of end-stage renal disease. We previously discovered that the BTBR mouse strain carrying the ob mutation at the leptin gene is an excellent model of human diabetic nephropathy and has been widely adopted by basic scientists and the pharmaceutical industry. Genetic factors play a role in susceptibility to diabetic nephropathy. We carried out a linkage study in a sample of mice generated from an intercross between the BTBR and C57BL/6J strains carrying the ob mutation. We identified a single locus and provided evidence that the leading candidate gene at this locus is nephrin. [ABSTRACT FROM AUTHOR]

Insufficient insulin secretion to meet metabolic demand results in diabetes. The intracellular flux of Ca 2+ into β-cells triggers insulin release. Since genetics strongly influences variation in islet secretory responses, we surveyed islet Ca 2+ dynamics in eight genetically diverse mouse strains. We found high strain variation in response to four conditions: (1) 8 mM glucose; (2) 8 mM glucose plus amino acids; (3) 8 mM glucose, amino acids, plus 10 nM glucose-dependent insulinotropic polypeptide (GIP); and (4) 2 mM glucose. These stimuli interrogate β-cell function, α- to β-cell signaling, and incretin responses. We then correlated components of the Ca 2+ waveforms to islet protein abundances in the same strains used for the Ca 2+ measurements. To focus on proteins relevant to human islet function, we identified human orthologues of correlated mouse proteins that are proximal to glycemic-associated single-nucleotide polymorphisms in human genome-wide association studies. Several orthologues have previously been shown to regulate insulin secretion (e.g. ABCC8, PCSK1, and GCK), supporting our mouse-to-human integration as a discovery platform. By integrating these data, we nominate novel regulators of islet Ca 2+ oscillations and insulin secretion with potential relevance for human islet function. We also provide a resource for identifying appropriate mouse strains in which to study these regulators., Competing Interests: CE, LC, BY, KS, SS, DS, KM, MM, MK, AA No competing interests declared, (© 2023, Emfinger, Clark et al.)