Differential Expression of Wnt Signaling Genes in African Versus European Inherited Mitochondrial DNA Haplogroups: Implications for Retinal Diseases.

Abstract

 

Purpose

 

Wnt signaling is a multifunctional pathway that regulates cellular division, apoptosis, stem cell maintenance and carcinogenesis. Studies have shown that this pathway is activated in the retinal pigment epithelium of animal models of age-related macular degeneration (AMD), diabetic retinopathy (DR) and retinitis pigmentosa (RP). Mitochondrial DNA (mtDNA) haplogroups are defined by accumulation of single nucleotide polymorphisms (SNPs) that represent different geographic origins of populations. Haplogroup H represents European-Caucasian populations and haplogroup L represents African origin populations. Individuals with haplogroup H mtDNA are lower risk for AMD. Haplogroup L individuals rarely develop wet AMD but have a high predisposition to develop diabetes and other inflammatory disorders. Cybrids (cytoplasmic hybrids) are created by introducing the mitochondria from individuals with either H haplogroup or L haplogroup into a host cell line that has been depleted of mitochondria (Rho0), so all cybrids carry the same nuclear genes but vary only in their mitochondrial DNA. The purpose of this study is to identify differences in expression levels for Wnt pathway genes between cybrids with haplogroups H versus L.

 

Methods

 

Mitochondria-deficient (Rho0) human ARPE-19 cells were fused with platelets from individuals with mtDNA haplogroups H (n=3) or L (n=3) to establish cybrid cell lines. Q-PCR was performed using primers for various genes associated with the Wnt pathway.

 

Results

 

Although the cybrids had identical nuclei, gene expression levels were significantly different in L cybrids relative to H cybrids for components of the Wnt pathway, including SFRP1 (0.2 fold, p=0.0035), KREMEN1 (1.28 fold, p=0.007), and RPS6KA4 (1.6 fold, p=0.035). Expression levels of other members of the Wnt pathway, including CSNK1E, WNT9A, LRP1, DKK3, MDM2, GSK3A and TGFβ were not found to be significantly different in the L cybrids versus the H cybrids.

 

Conclusions

 

Our experimental study demonstrates that SNP variations in mtDNA associated with H (European origin) and L (African origin) cybrids can influence nuclear gene expression in RPE cells and modulate the Wnt signaling pathway. These findings need to be further investigated to study their role in development of various retinal diseases.

 

Keywords: 533 gene/expression • 412 age-related macular degeneration • 701 retinal pigment epithelium