Systemic loss of Rubicon aggravates pathological features in the SOD1G93A mouse model

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease associated with motor neuron death. Superoxide dismutase 1 (SOD1) misfolding and aggregation have been linked to familial and sporadic ALS, where either mutant or wild-type SOD1 species abnormally accumulate as observed in postmortem tissue of ALS cases. These SOD1 species are toxic and contribute to motoneuron cell death. A dysregulation of the autophagy pathway has been widely observed in ALS. Previously, we found that Rubicon, a negative regulator of autophagy and endocytosis was upregulated in postmortem spinal cord tissue from sporadic ALS patients and in two ALS mouse models during the symptomatic stage of the disease. Here we found that overexpression of Rubicon in a motoneuron cell line led to marked increase in mutant SOD1 aggregation. Hence, we investigated the effects of Rubicon loss of function in the context of the SOD1 G93A ALS mouse model on disease progression and outcome. SOD1 G93A /Rub −/− mice exhibited an earlier disease onset and shorter lifespan than did littermate SOD1 G93A /Rub +/+ mice. Although we observed motor function loss in phenotypic analyses, no changes in microgliosis, astrogliosis, the number of motor neurons or levels of misfolded SOD1 aggregates were detected in vivo . Nevertheless, in vitro experiments showed Rubicon loss-of function in a motor neuron cell line increased mutant SOD1 aggregation, just like its overexpression, however with no adverse effect on motor neuron viability. These results suggest that Rubicon loss-of-function has unforeseen detrimental effects in vivo , highlighting a requirement for a cell-type specific fine-tuned balance of autophagy regulators.