PKB/AKT attenuates Lewy Body-like pathology in primary neurons via Cathepsins B and D

Motor symptoms of Parkinsons disease (PD) are caused by the loss of dopamine neurons in the substantia nigra pars compacta. Current PD therapies offer only symptomatic relief, and the research on novel ways to stop or slow down the degeneration of dopamine neurons in PD attracts considerable efforts. A characteristic feature of PD is the abnormal accumulation and spread of misfolded -synuclein (-syn) protein leading to the formation of Lewy neurites and bodies in different neuronal populations, including dopamine neurons. The process of Lewy body formation compromises neuronal functions and contributes to the progression of the disease and neurodegeneration in PD patients. Treatments preventing -syn misfolding, aggregation and/or spread may therefore provide much-needed disease-modifying therapies for PD. We and others have demonstrated that -syn aggregation and Lewy body formation can be modelled in primary neuronal cultures treated with -syn pre-formed fibrils (PFFs). Using this approach, we have identified several factors preventing the accumulation of phosphorylated -syn in dopamine neurons in vitro and in vivo. In particular, we and others have demonstrated a prominent role of PKB/AKT pathway activation in promoting the survival of dopamine neurons. Here, we utilize lentiviral vectors (LVs) to express constitutively active myristoylated serine-threonine protein kinase AKT1 (mAKT1) in primary dopamine neurons. We show that lentivirally-delivered mAKT1 promoted survival of dopamine neurons after thapsigargin-induced endoplasmic reticulum (ER) stress and prevented fibril-induced accumulation of phosphorylated -syn. Furthermore, using pharmacological tools, we demonstrate that this activity of mAKT1 is dependent on the functional Cathepsins B and D. These proof-of-principle results demonstrate the critical importance of lysosomal enzymes for processing misfolded -syn and establish a basis for the use of LVs to develop neuroprotective gene therapy strategies for dopamine neurons in PD.