Lower Circulating Folate Induced by a Fidgetin Intronic Variant is Associated with Reduced Congenital Heart Disease Susceptibility
Background—Folate deficiency is an independent risk factor for congenital heart disease (CHD); however, the maternal plasma folate level is paradoxically not a good diagnostic marker. Genome-wide surveys have identified variants of non-folate metabolic genes associated with the plasma folate level, suggesting that these genetic polymorphisms are potential risk factors for CHD.
Methods—To examine the effects of folate concentration-related variations on CHD risk in the Han Chinese population, we performed three independent case-control studies including a total of 1,489 CHD patients and 1,745 controls. The expression of the Fidgetin (FIGN) was detected in human cardiovascular and decidua tissue specimens using qRT-PCR and western blotting. The molecular mechanisms were investigated by luciferase reporter assays, surface plasmon resonance, and chromatin immunoprecipitation. FIGN-interacting proteins were confirmed by tandem affinity purification and co-immunoprecipitation. Proteasome activity and metabolite concentrations in the folate pathway were quantified using a commercial proteasome activity assay and immunoassays, respectively.
Results—The +94762G>C (rs2119289) variant in intron 4 of the FIGN gene was associated with significant reduction in CHD susceptibility (P = 5.1 × 10-14 for the allele, P = 8.5 × 10-13 for the genotype). Analysis of combined samples indicated that CHD risks in individuals carrying heterozygous (GC) or homozygous (CC) genotypes were reduced by 44% (odds ratio [OR] = 0.56, 95% confidence interval [CI] = 0.47-0.67) and 66% (OR = 0.34, 95% CI = 0.23-0.50), respectively, compared to those with the major GG genotype. Minor C allele carriers who had decreased plasma folate levels exhibited significantly increased FIGN expression because the transcription suppressor CREB1 did not bind the alternative promoter of FIGN isoform X3. Mechanistically, increased FIGN expression led to the accumulation of both reduced folate carrier 1 (RFC1) and dihydrofolate reductase (DHFR) via inhibition of their proteasomal degradation, which promoted folate absorption and metabolism.
Conclusions—We report a previously undocumented finding that decreased circulating folate levels induced by increased folate transmembrane transport and utilization, as determined by the Fidgetin intronic variant, serves as a protective mechanism against CHD. Our results may explain why circulating folate levels do not have a good diagnostic value.
- Received August 24, 2016.
- Revision received February 13, 2017.
- Accepted March 7, 2017.