Dopamine D2 receptor-mediated neuroprotection in a G2019S Lrrk2 genetic model of Parkinson’s disease

Abstract

Parkinson’s disease (PD) is a neurodegenerative disorder in which genetic and environmental factors synergistically lead to loss of midbrain dopamine (DA) neurons. Mutation of leucine-rich repeated kinase2 (Lrrk2) genes is responsible for the majority of inherited familial cases of PD and can also be found in sporadic cases. The pathophysiological role of this kinase has to be fully understood yet. Hyperactivation of Lrrk2 kinase domain might represent a predisposing factor for both enhanced striatal glutamatergic release and mitochondrial vulnerability to environmental factors that are observed in PD. To investigate possible alterations of striatal susceptibility to mitochondrial dysfunction, we performed electrophysiological recordings from the nucleus striatum of a G2019S Lrrk2 mouse model of PD, as well as molecular and morphological analyses of G2019S Lrrk2-expressing SH-SY5Y neuroblastoma cells. In G2019S mice, we found reduced striatal DA levels, according to the hypothesis of alteration of dopaminergic transmission, and increased loss of field potential induced by the mitochondrial complex I inhibitor rotenone. This detrimental effect is reversed by the D2 DA receptor agonist quinpirole via the inhibition of the cAMP/PKA intracellular pathway. Analysis of mitochondrial functions in G2019S Lrrk2-expressing SH-SY5Y cells revealed strong rotenone-induced oxidative stress characterized by reduced Ca2+ buffering capability and ATP synthesis, production of reactive oxygen species, and increased mitochondrial fragmentation. Importantly, quinpirole was able to prevent all these changes. We suggest that the G2019S-Lrrk2 mutation is a predisposing factor for enhanced striatal susceptibility to mitochondrial dysfunction induced by exposure to mitochondrial environmental toxins and that the D2 receptor stimulation is neuroprotective on mitochondrial function, via the inhibition of cAMP/PKA intracellular pathway. We suggest new possible neuroprotective strategies for patients carrying this genetic alteration based on drugs specifically targeting Lrrk2 kinase domain and mitochondrial functionality.

Pathogenic LRRK2 R1441C mutation is associated with striatal alterations

“…We also examined for changes in capacitance in GS mice. In line with previous findings [50,51] , we found no changes in the intrinsic properties of SPNs in the GS mice. We found no differences in membrane capacitance between GS mutant or WT The hypoexcitability of iSPNs in models of PD has been suggested as a homeostatic response to an increased corticostriatal transmission [50,52,53] , we thus examined possible presynaptic changes in corticostriatal transmission by measuring the paired-pulse ratios (PPRs) of the corticostriatal responses in WT and RC mice (see…”

“…Using microdialysis, reduced extracellular levels of dopamine at twelve months but not six months were reported [21] . In contrast, by using amperometry Tozzi et al reported reduced striatal dopamine levels in mice at six months [51] . Moreover, a recent report showed no difference on peak dopamine dopamine release in slices of three months [50] .…”

“…The most parsimonious explanation is the difference in expression levels of mutant LRRK2 in the presence of endogenous LRRK2, as well as the different promoters used to drive the expression of mutant protein [18] . In this study, by using RC and GS KI mice that express the mutant LRRK2 protein with endogenous expression patterns and levels, we performed a systematic comparative study between these two Lrrk2 KI mouse models to resolve conflicting reports of dopamine transmission [21,51] . We found a decrease in nigrostriatal dopamine release in both RC and GS mice.…”

Pathway-specific deregulation of striatal excitatory synapses in LRRK2 mutations

“…Moreover, dSPNs and iSPNs exhibit opposing PKA pathway signaling properties after dopamine receptor activation 45,40 . Given the critical role of LRRK2 in synaptic PKA activities 12,46 , these mutations are poised to have pathway specific effects and present distinct opportunities for pathway-targeted therapies.…”

Long-Term Exposure to PFE-360 in the AAV-α-Synuclein Rat Model: Findings and Implications

“…Another possibility is that the function of LRRK2 inhibition needs an external trigger to reveal its functional involvement in neurotransmission such as impaired DAergic neurotransmission in substantia nigra and striatum. In this respect, alterations in glutamatergic transmission in striatal slices from G2019S-LRRK2 transgenic animals were only observed when rotenone, a mitochondrial toxin, was also present, indicating that LRRK2 might only play a role in the diseased state, such as impaired DAergic neurotransmission (Tozzi et al, 2018). In support, recent studies have suggested that LRRK2 kinase activity is increased in substantia nigra in the AAV-␣-synuclein overexpression model and in rotenone models as well as in postmortem tissue from idiopathic PD patients (Howlett et al, 2017;Di Maio et al, 2018).…”