Functional genomic studies of aldo-keto reductases

Aldose reductase (AR) is considered a potential mediator of diabetic complications and is a drug target for inhibitors of diabetic retinopathy and neuropathy in clinical trials. However, the physiological role of this enzyme still has not been established. Since effective inhibition of diabetic complications will require early intervention, it is important to delineate whether AR fulfills a physiological role that cannot be compensated by an alternate aldo-keto reductase. Functional genomics provides a variety of powerful new tools to probe the physiological roles of individual genes, especially those comprising gene families. Several eucaryotic genomes have been sequenced and annotated, including yeast, nematode and fly. To probe the function of AR, we have chosen to utilize the budding yeast Saccharomyces cerevisiae as a potential model system. Unlike Caenorhabditis elegans and D. melanogaster, yeast provides a more desirable system for our studies because its genome is manipulated more readily and is able to sustain multiple gene deletions in the presence of either drug or auxotrophic selectable markers. Using BLAST searches against the human AR gene sequence, we identified six genes in the complete S. cerevisiae genome with strong homology to AR. In all cases, amino acids thought to play important catalytic roles in human AR are conserved in the yeast AR-like genes. All six yeast AR-like open reading frames (ORFs) have been cloned into plasmid expression vectors. Substrate and AR inhibitor specificities have been surveyed on four of the enzyme forms to identify, which are the most functionally similar to human AR. Our data reveal that two of the enzymes (YDR368Wp and YHR104Wp) are notable for their similarity to human AR in terms of activity with aldoses and substituted aromatic aldehydes. Ongoing studies are aimed at characterizing the phenotypes of yeast strains containing single and multiple knockouts of the AR-like genes.