Inhibition of dynein ATPase activity reduces high molecular weight forms of misfolded proteins involved in motoneuron diseases

Spinal and bulbar muscular atrophy (SBMA) and Amyotrophic lateral sclerosis (ALS) are two adult onset motoneuron diseases caused by degeneration of specific classes of motoneuron. Different mutant proteins have been found involved in familiar forms of these diseases (e.g.: androgen receptor (AR), SOD1 and TDP43). All these proteins tend to misfold acquiring aberrant conformations, which aggregate. Aggregates may be protective by subtracting misfolded proteins, but they may also impair proteasome and autophagy, two major players of the protein quality control system (PQC). We recently showed that HSPB8 mediated autophagy reduces misfolded proteins aggregation, even when proteasome is inhibited. Dynein, by binding BAG3 and HSPB8, transports misfolded proteins to microtubule organization center (MTOC), where proteins are assembled in aggresome to be degraded by autophagy. Dynein also mediates autophagosome formation, by binding Ambra1-Beclin1-Vps34 complex that enable autophagosome nucleation. In SBMA cell model we found that dynein is sequestered into aggregates of mutant AR near MTOC. To analyze the role of dynein in SBMA and ALS we used EHNA, an inhibitor of dynein ATPase activity witch impairs dynein-mediated transport. In cell model of SBMA and ALS EHNA induced a drastic reduction of aggregates of the misfolded proteins: ARpolyQ, mutSOD1, and mutTDP43. EHNA, also, increased the solubility of misfolded ARpolyQ. BAG1, witch routes misfolding proteins to proteasome degradation or chaperone-mediated-autophagy, was found increased after EHNA treatment. Our data are in line with previous observation that showing an increase of survival of the double mutant mice for mutSOD1 and an inactive form of dynein. This suggests that dynein may mediate the process of aggregate formation during the PQC response.