Hsp70- and Hsp90-mediated proteasomal degradation underlies TPIsugarkill pathogenesis in Drosophila

Triosephosphate isomerase (TPI) deficiency is a severe glycolytic enzymopathy that causes progressive locomotor impairment and neurodegeneration, susceptibility to infection, and premature death. The recessive missense TPIsugarkill mutation in Drosophila melanogaster exhibits phenotypes analogous to human TPI deficiency such as progressive locomotor impairment, neurodegeneration, and reduced life span. We have shown that the TPIsugarkill protein is an active stable dimer; however, the mutant protein is turned over by the proteasome reducing cellular levels of this glycolytic enzyme. As proteasome function is often coupled with molecular chaperone activity, we hypothesized that TPIsugarkill is recognized by molecular chaperones that mediate the proteasomal degradation of the mutant protein. Coimmunoprecipitation data and analyses of TPIsugarkill turnover in animals with reduced or enhanced molecular chaperone activity indicate that both Hsp90 and Hsp70 are important for targeting TPIsugarkill for degradation. Furthermore, molecular chaperone and proteasome activity modified by pharmacological or genetic manipulations resulted in improved TPIsugarkill protein levels and rescue some but not all of the disease phenotypes suggesting that TPI deficiency pathology is complex. Overall, these data demonstrate a surprising role for Hsp70 and Hsp90 in the progression of neural dysfunction associated with TPI deficiency.

Research Highlights►HSP70 and HSP90 regulate TPI[sgk] turnover ►TPI[sgk] is a functional protein ►Degradation of TPI[sgk] underlies pathogenesis ►TPI[sgk] is a nonaggregated, cytosolic protein targeted for proteasomal degradation