Differential Expression of Wnt Genes in Transmitochondrial Cybrids with African-origin versus European-origin mtDNA

Abstract

 

Purpose

 

In the United States approximately 11% of all African-Americans, older than 20 years, have diabetes. Diabetes is a disease of metabolism and mitochondria (mt) play a key role. Human mtDNA can be categorized into haplogroups which are polymorphisms inherited along maternal lineages and define geographic origins of human populations. The most common European haplogroup is H and maternal African-origin haplogroup is L. The canonical Wnt pathway plays a key role in development of retinal vasculature and diabetic retinopathy. This study uses transmitochondrial cybrids to determine if L versus H haplogroups influence expression patterns of diabetes-associated genes.

 

Methods

 

Cybrid cell lines were established by fusing mitochondria-deficient human ARPE-19 cells with platelets from individuals of either European-origin (H, n=6) or African-origin L, n=8). Cybrids were cultured, RNA was extracted from each cybrid and cDNA synthesized. Q-PCR was performed using primers for genes associated with the Wnt pathway (DDK3, SFRP1, KREMEN1, GSK3A, and RARA1) and glucose metabolism and insulin signaling (RPS6KA4). For statistical analysis, a standard student’s t-test was used to measure the significant differences between gene expression levels using the delta-delta-Ct’s (ddCt) for each gene in L cybrids relative to H cybrids.

 

Results

 

The L cybrids had different expression levels for four Wnt-related genes compared to H cybrids: Expression for two Wnt inhibitors (DDK3, 0.06-fold, p = 0.03; SFRP1, 0.2-fold, p = 0.0035) were decreased while KREMEN1 expression was elevated (1.28-fold, p =0.007). There was an increased level for RPS6KA4, (1.6-fold, p = 0.035). The GSK3A and RARA1 gene expressions in the L cybrids were similar to the H cybrids (0.8-fold, p = 0.06 and 0.95-fold, p = 0.6, respectively).

 

Conclusions

 

Although all cybrids have identical nuclear genes, the expression levels of diabetes-related genes were significantly different in L versus H cybrids. Based upon our findings, we propose that a person’s mtDNA haplogroup background acts as a “modifier” for gene expression in major pathways related to diseases and this contributes to disparities found in diabetes and other ethnic/racial susceptible diseases. In addition, the Wnt pathway may be a potential target for therapy of diabetic retinopathy and other diseases with neovascular pathologies.