The free fatty acid receptor 3 (FFA3) is a nutrient sensor of gut microbiota-generated nutrients, the short-chain fatty acids. Previously, we have shown that FFA3 is expressed in β-cells and inhibits islet insulin secretion ex vivo. Here, we determined the physiological relevance of the above observation by challenging wild-type (WT) and FFA3 knockout (KO) male mice with 1) hyperglycemia and monitoring insulin response via highly sensitive hyperglycemic clamps, 2) dietary high fat (HF), and 3) chemical-induced diabetes. As expected, FFA3 KO mice exhibited significantly higher insulin secretion and glucose infusion rate in hyperglycemic clamps. Predictably, under metabolic stress induced by HF-diet feeding, FFA3 KO mice exhibited less glucose intolerance compared with the WT mice. Moreover, similar islet architecture and β-cell area in HF diet-fed FFA3 KO and WT mice was observed. Upon challenge with streptozotocin (STZ), FFA3 KO mice initially exhibited a tendency for an accelerated incidence of diabetes compared with the WT mice. However, this difference was not maintained. Similar glycemia and β-cell mass loss was observed in both genotypes 10 days post-STZ challenge. Higher resistance to STZ-induced diabetes in WT mice could be due to higher basal islet autophagy. However, this difference was not protective because in response to STZ, similar autophagy induction was observed in both WT and FFA3 KO islets. These data demonstrate that FFA3 plays a role in modulating insulin secretion and β-cell response to stressors. The β-cell FFA3 and autophagy link warrant further research.

Glucokinase (GCK) is the principal hexokinase (HK) in the liver, operating as a glucose sensor to regulate glucose metabolism and lipid homeostasis. Recently, we proposed HK domain-containing 1 (HKDC1) to be a fifth HK with expression in the liver. Here, we reveal HKDC1 to have low glucose-phosphorylating ability and demonstrate its association with the mitochondria in hepatocytes. As we have shown previously that genetic deletion of HKDC1 leads to altered hepatic triglyceride levels, we also explored the influence of overexpression of HKDC1 in hepatocytes on cellular metabolism, observing reduced glycolytic capacity and maximal mitochondrial respiration with concurrent reductions in glucose oxidation and mitochondrial membrane potential. Furthermore, we found that acute in vivo overexpression of HKDC1 in the liver induced substantial changes in mitochondrial dynamics. Altogether, these findings suggest that overexpression of HKDC1 causes mitochondrial dysfunction in hepatocytes. However, its overexpression was not enough to alter energy storage in the liver but led to mild improvement in glucose tolerance. We next investigated the conditions necessary to induce HKDC1 expression, observing HKDC1 expression to be elevated in human patients whose livers were at more advanced stages of nonalcoholic fatty liver disease (NAFLD) and similarly, found high liver expression in mice on diets causing high levels of liver inflammation and fibrosis. Overall, our data suggest that HKDC1 expression in hepatocytes results in defective mitochondrial function and altered hepatocellular metabolism and speculate that its expression in the liver may play a role in the development of NAFLD.

A role of the gut microbiota in the development of both type 1 and type 2 diabetes has been suggested. The free fatty acid receptor 3 (FFA3) is considered to be a nutrient sensor that may be mediating the gut microbiota actions via the gut microbial metabolites, short chain fatty acids. As this receptor is expressed in β cells, a suggested metabolic interface may be occurring between β cells and the gut microbiota. We have previously shown that FFA3 inhibits β cell function in islets ex vivo. Exploring the physiological relevance of this observation in vivo, male mice with genetic knockout (KO) of FFA3 and their wildtype (WT) littermates were characterized with regard to glucose homeostasis. It was found that FFA3‐KO mice exhibit significantly higher insulin secretion and glucose infusion rates in hyperglycemic clamps consistent with enhanced insulin secretion by FFA3‐KO islets ex vivo. No differences were observed in energy expenditure, glycemic status and insulin sensitivity in FFA3‐KO and WT mice. With the exception of significantly enhanced insulin secretion in FFA3‐KO as compared to the WT mice upon intraperitoneal glucose challenge, no overt metabolic phenotype was observed under normal physiologic conditions. To investigate if FFA3 contributes to the β cell response to stress, two different models were utilized. First, under metabolic stress induced by high fat diet feeding, the WT mice developed impaired glucose tolerance as compared to the FFA3‐KO mice, owing mainly to enhanced insulin secretion with FFA3‐KO mice. Despite less insulin secretion (50–70% lower as compared to FFA3‐KO mice), WT mice had similar islet architecture and islet mass as FFA3‐KO mice. Surprisingly, challenge with single high dose of streptozotocin (STZ, agent inducing β cell damage), led to accelerated incidence of diabetes development in FFA3‐KO mice compared to the WT mice. Additionally, greater insulin deficiency and decreased β cell mass was observed in FFA3‐KO mice following STZ treatment, as compared to WT mice. Taken together, FFA3 mediates insulin secretion and the β cell response to high fat diet feeding without alteration in the islet mass. FFA3 also regulates the β cell responses to STZ treatment. Thus, these data demonstrate that FFA3 plays an important role in insulin secretion and β cell response to stressors.Support or Funding InformationSupport for the project has been from the Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development, Career Development Grant No.1IK2BX001587‐01 (to B. T. Layden). M. Priyadarshini is supported by an American Heart Association postdoctoral fellowship (no. 15POST22410016).

In a recent genome-wide association study, hexokinase domain-containing protein 1, or HKDC1, was found to be associated with gestational glucose levels during 2-hour glucose tolerance tests at 28 weeks of pregnancy. Because our understanding of the mediators of gestational glucose homeostasis is incomplete, we have generated the first transgenic mouse model to begin to understand the role of HKDC1 in whole-body glucose homeostasis. Interestingly, deletion of both HKDC1 alleles results in in utero embryonic lethality. Thus, in this study, we report the in vivo role of HKDC1 in whole-body glucose homeostasis using a heterozygous-deleted HKDC1 mouse model (HKDC1(+/-)) as compared with matched wild-type mice. First, we observed no weight, fasting or random glucose, or fasting insulin abnormalities with aging in male and female HKDC1(+/-) mice. However, during glucose tolerance tests, glucose levels were impaired in both female and male HKDC1(+/-) mice at 15, 30, and 120 minutes at a later age (28 wk of age). These glucose tolerance differences also existed in the female HKDC1(+/-) mice at earlier ages but only during pregnancy. And finally, the impaired glucose tolerance in HKDC1(+/-) mice was likely due to diminished whole-body glucose use, as indicated by the decreased hepatic energy storage and reduced peripheral tissue uptake of glucose in HKDC1(+/-) mice. Collectively, these data highlight that HKDC1 is needed to maintain whole-body glucose homeostasis during pregnancy but also with aging, possibly through its role in glucose use.

Metastatic melanoma is an aggressive and deadly disease. The chemokine receptor CXCR4 is active in melanoma metastasis, although the mechanism for the promotion and maintenance of CXCR4 expression in these cells is mostly unknown. Here, we find melanoma cells express two CXCR4 isoforms, the common version and a variant that is normally restricted to cells during development or to mature blood cells. CXCR4 expression is driven through a highly conserved intronic enhancer element by the transcription factors PAX3 and FOXD3. Inhibition of these transcription factors slows melanoma cell growth, migration, and motility, as well as reduces CXCR4 expression. Overexpression of these transcription factors drives the production of increased CXCR4 levels. Loss of PAX3 and FOXD3 transcription factor activity results in a reduction in cell motility, migration, and chemotaxis, all of which are rescued by CXCR4 overexpression. Here, we discover a molecular pathway wherein PAX3 and FOXD3 promote CXCR4 gene expression in melanoma.

Pregnancy presents a unique physiological challenge that requires changes coordinated by placentally and non–placentally derived hormones to prepare the mother for the metabolic stress presented by fetal development and to ensure appropriate nutrient allocation between mother and fetus. Of particular importance is the maintenance of normal glucose metabolism during pregnancy. Here, we describe physiological changes in glucose metabolism during pregnancy and highlight new insights into these adaptations that have emerged over the past decade using novel methodologies, specifically genome-wide association studies (GWAS) and metabolomics. While GWAS have identified some novel associations with metabolic traits during pregnancy, the majority of the findings overlap with those observed in nonpregnant populations and individuals with type 2 diabetes (T2D). Metabolomics studies have provided new insight into key metabolites involved in gestational diabetes mellitus (GDM). Both of these approaches have suggested that a strong link exists between GDM and T2D. Most recently, a role of the gut microbiome in pregnancy has been observed, with changes in the microbiome during the third trimester having metabolic consequences for the mother. In this Perspectives in Diabetes article, we highlight how these new data have broadened our understanding of gestational metabolism, and emphasize the importance of future studies to elucidate differences between GDM and T2D.

1α,25-Dihydroxyvitamin D 3 [1α,25(OH) 2 D 3 ] is a steroid hormone derived from circulating 25(OH) vitamin D [25(OH)D] with chemopreventive effects in colorectal cancer. 1α,25(OH) 2 D 3 acts through transcriptional mechanisms; however, our understanding of vitamin D transcriptional responses in the colon is derived from studies in transformed cancer cell lines which may not represent responses in normal healthy tissue. Here, we describe the optimization of an ex vivo culture model using primary colonic biopsy samples for studying short-term transcriptional response induced by 1α,25(OH) 2 D 3 and 25(OH)D treatment. Colon biopsy samples from healthy subjects were maintained in primary culture and treated in parallel with 100 nM 1α,25(OH) 2 D 3 or 62.5 nM 25(OH)D and vehicle control (ethanol). Viability was assessed using histology and enzymatic assays. Genome-wide transcriptional responses to 1α,25(OH) 2 D 3 were assessed and expression of 25(OH)D targets CYP27B1 and CYP24A1 were measured by real time PCR. We show that ex vivo culture of colonic tissue remains viable for up to 8 h. The largest number of differentially expressed genes in response to 1α,25(OH) 2 D 3 was noted after 6 h ( n = 120). As proof of concept, the top upregulated gene was CYP24A1, a well-established vitamin D-responsive gene. With 25(OH)D treatment, mRNA expression of CYP27B1 was significantly increased after 1 h, while expression of CYP24A1 was greatest at 8 h. Ex vivo culture can be used to assess short-term transcriptional responses to 1α,25(OH) 2 D 3 and 25(OH)D in primary tissue from human colon. Future studies will address interindividual differences in transcriptional responses.

Maternal glucose levels during pregnancy impact the developing fetus, affecting metabolic health both early and later on in life. Both genetic and environmental factors influence maternal metabolism, but little is known about the genetic mechanisms that alter glucose metabolism during pregnancy. Here, we report that haplotypes previously associated with gestational hyperglycaemia in the third trimester disrupt regulatory element activity and reduce expression of the nearby HKDC1 gene. We further find that experimentally reducing or increasing HKDC1 expression reduces or increases hexokinase activity, respectively, in multiple cellular models; in addition, purified HKDC1 protein has hexokinase activity in vitro . Together, these results suggest a novel mechanism of gestational glucose regulation in which the effects of genetic variants in multiple regulatory elements alter glucose homeostasis by coordinately reducing expression of the novel hexokinase HKDC1 .

Genome-wide association studies (GWAS) in colorectal cancer (CRC) identified five regions near transforming growth factor β-related genes BMP4, GREM1, CDH1, SMAD7 and RPHN2. The true risk alleles remain to be identified in these regions, and their role in CRC risk in non-European populations has been understudied. Our previous work noted significant genetic heterogeneity between African Americans (AAs) and European Americans (EAs) for single nucleotide polymorphisms (SNPs) identified in GWAS. We hypothesized that associations may not have been replicated in AAs due to differential or independent genetic structures. In order to test this hypothesis, we genotyped 195 tagging SNPs across these five gene regions in 1194 CRC cases (795 AAs and 399 EAs) and 1352 controls (985 AAs and 367 EAs). Imputation was performed, and association testing of genotyped and imputed SNPs included ancestry, age and sex as covariates. In two of the five genes originally associated with CRC, we found evidence for association in AAs including rs1862748 in CDH1 (OR(Add) = 0.82, P = 0.02) and in GREM1 the SNPs rs10318 (OR(Rec) = 60.1, P = 0.01), rs11632715 (OR(Rec) = 2.36; P = 0.004) and rs12902616 (OR(Rec) = 1.28, P = 0.005), the latter which is in linkage disequilibrium with the previously identified SNP rs4779584. Testing more broadly for associations in these gene regions in AAs, we noted three statistically significant association peaks in GREM1 and RHPN2 that were not identified in EAs. We conclude that some CRC risk alleles are shared between EAs and AAs and others are population specific.

Abstract Background: Genome-wide association studies (GWAS) of colorectal cancer (CRC) have identified risk variants in candidate genes involved in TGF-ß signaling including BMP4, GREM1, CDH1, RHPN2 and SMAD7. We previously replicated the association with a 3′-UTR SNP in GREM1 (rs10318) in African Americans but did not find evidence of associations in the other genes. This finding could be explained by different genomic structure in African Americans. Therefore, we sought to fine-map these genes to identify CRC risk variants in African Americans who are at highest risk of CRC in the US. Methods: DNA from cases and controls was obtained from two US institutions. In total, we included DNA from 795 AA cases and 985 AA controls. TagSNPs with minor allele frequencies >5% and pairwise r2 >0.8 were identified in five genes using YRI Hapmap data. A total of 81 SNPs were genotyped in cases and controls using Sequenom MassARRAY. We calculated odds ratios and 95% confidence intervals using logistic regression controlling for ancestry, age, gender and multiple testing in PLINK. Results: Association analysis was completed for four genes: BMP4, GREM1, CDH1 and RHPN2. The top tagSNP associations for each gene are shown in the Table. None of the SNPs were significant after permutation testing. In GREM1, the strongest SNP associations were found at the 3′ end of the gene. In BMP4, we identified two SNPs (rs1957852 and rs7146040) that are in LD with rs4444235 previously identified in a European GWAS. In CDH1, rs12931189 is located in the same LD block as the strongest association signal (rs7199991) in a recent fine-mapping study in Europeans. Finally, we have no evidence for associations in RHPN2 in African Americans. Conclusion: These results provide preliminary evidence of associations in African American colorectal cancer patients in BMP4, GREM1 and CDH1 identified by GWAS in Europeans. Ongoing work is testing associations in SMAD7 and further fine-mapping by imputation and resequencing in these regions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1661. doi:1538-7445.AM2012-1661

Low vitamin D levels are associated with an increased incidence of colorectal cancer (CRC) and higher mortality from the disease. In the US, African Americans (AAs) have the highest CRC incidence and mortality and the lowest levels of vitamin D. Single nucleotide polymorphisms (SNPs) in the vitamin D receptor (VDR) gene have been previously associated with CRC, but few studies have included AAs. We studied 795 AA CRC cases and 985 AA controls from Chicago and North Carolina as well as 1324 Caucasian cases and 990 Caucasian controls from Chicago and Spain. We genotyped 54 tagSNPs in VDR (46586959 to 46521297 Mb) and tested for association adjusting for West African ancestry, age, gender, and multiple testing. Untyped markers were imputed using MACH1.0. We analyzed associations by gender and anatomic location in the whole study group as well as by vitamin D intake in the North Carolina AA group. In the joint analysis, none of the SNPs tested was significantly associated with CRC. For four previously tested restriction fragment length polymorphisms, only one (referred to as ApaI), tagged by the SNP rs79628898, had a nominally significant p-value in AAs; none of these polymorphisms were associated with CRC in Caucasians. In the North Carolina AAs, for whom we had vitamin D intake data, we found a significant association between an intronic SNP rs11574041 and vitamin D intake, which is evidence for a VDR gene-environment interaction in AAs. In summary, using a systematic tagSNP approach, we have not found evidence for significant associations between VDR and CRC in AAs or Caucasians.

Transcription factors initiate programs of gene expression and are catalysts in downstream molecular cascades that modulate a variety of cellular processes. Pax3 is a transcription factor that is important in the melanocyte and influences melanocytic proliferation, resistance to apoptosis, migration, lineage specificity and differentiation. In this review, we focus on Pax3 and the molecular pathways that Pax3 is a part of during melanogenesis and in the melanocyte stem cell. These roles of Pax3 are emphasized during the development of diseases and syndromes resulting from either too much or too little Pax3 function. Due to its key task in melanocyte stem cells and tumors, the Pax3 pathway may provide an ideal target for either stem cell or cancer therapies.