Figure 7: The combined treatment with AAVs abrogates INIs and restores normal PABPN1 expression improving both the gain of toxic function (GF) and the loss of physiological function (LF) mechanisms of the disease in the A17 mouse model.

(a) In wild-type FvB skeletal muscle, the endogenous wild-type PABPN1 (green) moves to the nucleus where it can function normally. The amount of normal PABPN1 that achieves the threshold for the optimal cell survival and functionality as shown in the graph in the upper left side. There is no loss of function (LF) or gain of function (GF), labelled with N (Not). (b) In A17 mice the expression of expPABPN1 (red) induces aggregate formation where normal PABPN1 and several other proteins as well as polyA RNAs are trapped. This might respectively induce both a loss of function (LF) associated to a minor amount of normal PABPN1 available and a toxic gain of function (GF) due to the sequestration of other macromolecules associated to dysregulated biological pathways, labelled as Y (Yes). (c) After injection of AAV-optPABPN1, the newly expressed optPABPN1 (blue) counteracts the lack of available normal PABPN1 (that is, it may reduce the loss of function mechanism of the disease) but it does not affect aggregate formation nor the toxic gain of function mechanism. No improvement of the pathology is observed. (d) By delivering ddRNAi to knockdown endogenous PABPN1, and after its conversion to siRNA by DICER and RISC complexes, aggregates are abrogated and this is likely associated to a reduction on the gain-of-function mechanism. However the normal PABPN1 downregulation promotes muscle degeneration. Again, no improvement of the pathology is observed. (e) Only the co-injection of the two vectors inhibits the aggregate formation while rescuing the normal PABPN1 to the level vital for optimal cell survival and functionality in A17 muscles (suggesting that both the toxic gain of function and the loss of function effect might be significantly reduced).