a control siRNA, indeed confirming that Hsp40 inhibits polyQ protein secretion. These results imply that inhibition of secretion of the polyQ protein from cells by Hsp40 results in a non cellautonomous therapeutic effect in R6/2 mouse brains, possibly via inhibition of the cell-cell transmission of the pathogenic polyQ protein. Discussion In this study we show for the first time that viral vectormediated expression of a molecular chaperone, namely Hsp40 significantly improves the neurological phenotypes of a mouse model of the polyQ diseases. Although a recent study reported the effectiveness of another Hsp40 family member, HSJ1a in R6/2 mice, this study cannot be directly translated to a therapy since it was performed by the crossing of transgenic mice. In addition, although lentiviral vector-mediated delivery of DNAJB2a to a polyQ disease rat model has been investigated, it did not demonstrate the therapeutic effect on the neurological phenotypes, perhaps because of 
the limited spread of lentiviruses. We successfully overcame these above problems by using AAV, which infects a widespread area of the brain, and is already used in human patients. We did not detect significant therapeutic effects of AAV5Hsp70 on R6/2 mice unlike AAV5-Hsp40, possibly due to the very low infection rate of our AAV5-Hsp70, or differences in the effectiveness of Hsp40 and Hsp70 against mutant htt. Indeed, previous studies examining the effect of Hsp70 in R6/ 2 mice have shown no or very modest therapeutic effects. Furthermore, a cell culture study demonstrated that Hsp40 family members are effective against the toxicity of mutant htt, while Hsp70 family members are ineffective. Taken together, these studies indicate that Hsp40 family members may be more effective than Hsp70 family members against the toxic effects of mutant htt. We surprisingly found that AAV5-Hsp40 inhibits inclusion body formation also in virus non-infected cells, suggesting a non cell-autonomous therapeutic effect. Aggregation prone proteins that cause neurodegenerative diseases including pathogenic polyQ proteins, as well as a-synuclein which causes Parkinson’s disease, and tau which causes the tauopathies have recently been suggested to be transmitted between cells, and this may be the mechanism leading to the progressive spread of neuropathology in these diseases. We detected a significant amount of the pathogenic polyQ protein in the culture medium of Neuro2A cells, suggesting its cell-cell transmission, which is compatible with previous studies. We further found that Hsp40 suppresses secretion of the pathogenic polyQ protein from cells, suggesting that it may inhibit the cell-cell transmission of the pathogenic polyQ protein. The non-cell autonomous therapeutic effect of Hsp40 may also involve other mechanisms, such as AAV5-Hsp40 infected neurons may MedChemExpress ONX-0914 create a better environment for contacting non-infected neurons or Hsp40 itself may be secreted to exert therapeutic effects on neighboring non-infected neurons, as is suggested for Hsp70. We were unable to detect the therapeutic effect of AAV5-QBP1 on the neurological phenotypes of R6/2 mice, although we successfully detected its inhibition of inclusion body formation. However, we and others have previously shown that expression of QBP1 exerts therapeutic effects on the neurological phenotypes of Drosophila and mouse models of the polyQ diseases. Since the infection efficiency of all of the viruses used in this study was quite low, the ex
