A Parkinson's disease gene regulatory network identifies the signaling protein RGS2 as a modulator of LRRK2 activity and neuronal toxicity

Abstract

Mutations in LRRK2 are one of the primary genetic causes of Parkinson's disease (PD). LRRK2 contains a kinase and a GTPase domain, and familial PD mutations affect both enzymatic activities. However, the signaling mechanisms regulating LRRK2 and the pathogenic effects of familial mutations remain unknown. Identifying the signaling proteins that regulate LRRK2 function and toxicity remains a critical goal for the development of effective therapeutic strategies. In this study, we apply systems biology tools to human PD brain and blood transcriptomes to reverse-engineer a LRRK2-centered gene regulatory network. This network identifies several putative master regulators of LRRK2 function. In particular, the signaling gene RGS2, which encodes for a GTPase-activating protein (GAP), is a key regulatory hub connecting the familial PD-associated genes DJ-1 and PINK1 with LRRK2 in the network. RGS2 expression levels are reduced in the striata of LRRK2 and sporadic PD patients. We identify RGS2 as a novel interacting partner of LRRK2 in vivo. RGS2 regulates both the GTPase and kinase activities of LRRK2. We show in mammalian neurons that RGS2 regulates LRRK2 function in the control of neuronal process length. RGS2 is also protective against neuronal toxicity of the most prevalent mutation in LRRK2, G2019S. We find that RGS2 regulates LRRK2 function and neuronal toxicity through its effects on kinase activity and independently of GTPase activity, which reveals a novel mode of action for GAP proteins. This work identifies RGS2 as a promising target for interfering with neurodegeneration due to LRRK2 mutations in PD patients.

Understanding the GTPase Activity of LRRK2: Regulation, Function, and Neurotoxicity

“…A second putative GAP-like protein, RGS2, has also been identified for LRRK2. RGS2 was originally identified in a C.elegans screen as a genetic modifier of the susceptibility of LRRK2 transgenic worms to rotenone-induced dopaminergic neuronal loss [46]. RGS2 was subsequently shown to interact with LRRK2, enhance its GTP hydrolysis activity in vitro, and also serve as a modest substrate of LRRK2 kinase activity [46].…”

“…RGS2 was originally identified in a C.elegans screen as a genetic modifier of the susceptibility of LRRK2 transgenic worms to rotenone-induced dopaminergic neuronal loss [46]. RGS2 was subsequently shown to interact with LRRK2, enhance its GTP hydrolysis activity in vitro, and also serve as a modest substrate of LRRK2 kinase activity [46]. However, opposite to the effects of ArfGAP1, RGS2 reduces LRRK2 kinase activity in vitro, and RGS2 overexpression rescues LRRK2-induced neuronal toxicity suggesting a neuroprotective capacity [46].…”

“…RGS2 was subsequently shown to interact with LRRK2, enhance its GTP hydrolysis activity in vitro, and also serve as a modest substrate of LRRK2 kinase activity [46]. However, opposite to the effects of ArfGAP1, RGS2 reduces LRRK2 kinase activity in vitro, and RGS2 overexpression rescues LRRK2-induced neuronal toxicity suggesting a neuroprotective capacity [46]. How these distinct GAPs both acting upon the GTPase domain can have opposing effects on LRRK2 kinase activity and neuronal toxicity remains to be clarified.…”

“…A prior study suggested that disruption of GTP binding (via K1347A) can rescue neuronal toxicity induced by G2019S LRRK2 [34], although it is likely that neuroprotection may result instead from the impaired dimerization and destabilization of LRRK2 known to be caused by the K1347A variant in neurons [15]. As mentioned above, ArfGAP1 expression is required for G2019S LRRK2-induced neuronal toxicity, whereas RGS2 is neuroprotective [42, 46]. It is not known whether these GAPs act upon LRRK2 GTPase or kinase activity to regulate neurotoxicity or whether they act in pathways downstream of LRRK2 potentially as GTPase effectors or kinase substrates.…”

Cellular processes associated with LRRK2 function and dysfunction

“…Furthermore, using a systems biology approach, Dusonchet et al . 43 identified regulator of G‐protein signalling 2 (RGS2) as an interactor able to regulate LRRK2 kinase and GTPase activities in vitro in a synergistic manner. Clearly, the enzyme activities of LRRK2 undergo intramolecular regulations that can also be influenced by other LRRK2 interactors.…”