A single nucleotide polymorphism within the acetyl-coenzyme A carboxylase beta gene is associated with proteinuria in patients with type 2 diabetes

Abstract

It has been suggested that genetic susceptibility plays an important role in the pathogenesis of diabetic nephropathy. A large-scale genotyping analysis of gene-based single nucleotide polymorphisms (SNPs) in Japanese patients with type 2 diabetes identified the gene encoding acetyl-coenzyme A carboxylase beta (ACACB) as a candidate for a susceptibility to diabetic nephropathy; the landmark SNP was found in the intron 18 of ACACB (rs2268388: intron 18 +4139 C > T, p = 1.4x10(-6), odds ratio = 1.61, 95% confidence interval [CI]: 1.33-1.96). The association of this SNP with diabetic nephropathy was examined in 9 independent studies (4 from Japan including the original study, one Singaporean, one Korean, and two European) with type 2 diabetes. One case-control study involving European patients with type 1 diabetes was included. The frequency of the T allele for SNP rs2268388 was consistently higher among patients with type 2 diabetes and proteinuria. A meta-analysis revealed that rs2268388 was significantly associated with proteinuria in Japanese patients with type 2 diabetes (p = 5.35 x 10(-8), odds ratio = 1.61, 95% Cl: 1.35-1.91). Rs2268388 was also associated with type 2 diabetes-associated end-stage renal disease (ESRD) in European Americans (p = 6 x 10(-4), odds ratio = 1.61, 95% Cl: 1.22-2.13). Significant association was not detected between this SNP and nephropathy in those with type 1 diabetes. A subsequent in vitro functional analysis revealed that a 29-bp DNA fragment, including rs2268388, had significant enhancer activity in cultured human renal proximal tubular epithelial cells. Fragments corresponding to the disease susceptibility allele (T) had higher enhancer activity than those of the major allele. These results suggest that ACACB is a strong candidate for conferring susceptibility for proteinuria in patients with type 2 diabetes.

Figure 1. Schematic view of the association of SNPs in the ACACB region with diabetic nephropathy.

(A) Pairwise correlation structure at a 200-kb interval around SNP rs2268338 analyzed by Haploview (Haploview: http://www.broadinstitute.org/haploview/haploview). The plot includes pairwise r² values from the HapMap release 24 for the JPT population. (B) Genes located at this locus. The asterisk indicates the SNP rs2268388 at intron 18 of the ACACB. (C) Results of a case-control association study for diabetic nephropathy in 754 Japanese individuals with type 2 diabetes having overt proteinuria and 558 control individuals with type 2 diabetes and normoalbuminuria. The log₁₀-transformed p values for an additive model are plotted on the Y-axis. The X-axis indicates chromosomal position at this locus.

Figure 2. Expression profiles of ACACB.

(A) Expression profiles of ACACB in various human tissues evaluated by real-time PCR. (B) Results of in situ hybridization for 20-week-old normal mouse kidneys using mouse Acacb anti-sense (left) and sense (right) probes.

Figure 3. Effect of a 29-bp DNA fragment containing the associated SNP (rs2268388) on transcriptional activity in cultured hRPTECs.

(A) A 29-bp sequence including SNP rs2268338. Overhung sequences are compatible ends for concatenation. (B) Enhancer activities of the DNA fragments corresponding to each allele in human RPTECs. Results are shown as mean ± SD of the ratio of activity to that of the promoter alone obtained from 4 independent experiments. * p = 0.045 vs. major allele.