Neurodegenerative phenotypes in an A53T α-synuclein transgenic mouse model are independent of LRRK2.

Mutations in the genes encoding LRRK2 and α-synuclein cause autosomal dominant forms of familial Parkinson's disease (PD). Fibrillar forms of α-synuclein are a major component of Lewy bodies, the intracytoplasmic proteinaceous inclusions that are a pathological hallmark of idiopathic and certain familial forms of PD. LRRK2 mutations cause late-onset familial PD with a clinical, neurochemical and, for the most part, neuropathological phenotype that is indistinguishable from idiopathic PD. Importantly, α-synuclein-positive Lewy bodies are the most common pathology identified in the brains of PD subjects harboring LRRK2 mutations. These observations may suggest that LRRK2 functions in a common pathway with α-synuclein to regulate its aggregation. To explore the potential pathophysiological interaction between LRRK2 and α-synuclein in vivo, we modulated LRRK2 expression in a well-established human A53T α-synuclein transgenic mouse model with transgene expression driven by the hindbrain-selective prion protein promoter. Deletion of LRRK2 or overexpression of human G2019S-LRRK2 has minimal impact on the lethal neurodegenerative phenotype that develops in A53T α-synuclein transgenic mice, including premature lethality, pre-symptomatic behavioral deficits and human α-synuclein or glial neuropathology. We also find that endogenous or human LRRK2 and A53T α-synuclein do not interact together to influence the number of nigrostriatal dopaminergic neurons. Taken together, our data suggest that α-synuclein-related pathology, which occurs predominantly in the hindbrain of this A53T α-synuclein mouse model, occurs largely independently from LRRK2 expression. These observations fail to provide support for a pathophysiological interaction of LRRK2 and α-synuclein in vivo, at least within neurons of the mouse hindbrain.

Dopaminergic neuronal loss, reduced neurite complexity and autophagic abnormalities in transgenic mice expressing G2019S mutant LRRK2.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause late-onset, autosomal dominant familial Parkinson's disease (PD) and also contribute to idiopathic PD. LRRK2 mutations represent the most common cause of PD with clinical and neurochemical features that are largely indistinguishable from idiopathic disease. Currently, transgenic mice expressing wild-type or disease-causing mutants of LRRK2 have failed to produce overt neurodegeneration, although abnormalities in nigrostriatal dopaminergic neurotransmission have been observed. Here, we describe the development and characterization of transgenic mice expressing human LRRK2 bearing the familial PD mutations, R1441C and G2019S. Our study demonstrates that expression of G2019S mutant LRRK2 induces the degeneration of nigrostriatal pathway dopaminergic neurons in an age-dependent manner. In addition, we observe autophagic and mitochondrial abnormalities in the brains of aged G2019S LRRK2 mice and markedly reduced neurite complexity of cultured dopaminergic neurons. These new LRRK2 transgenic mice will provide important tools for understanding the mechanism(s) through which familial mutations precipitate neuronal degeneration and PD.

Conditional transgenic mice expressing C-terminally truncated human alpha-synuclein (alphaSyn119) exhibit reduced striatal dopamine without loss of nigrostriatal pathway dopaminergic neurons.

BACKGROUND: Missense mutations and multiplications of the alpha-synuclein gene cause autosomal dominant familial Parkinson's disease (PD). alpha-Synuclein protein is also a major component of Lewy bodies, the hallmark pathological inclusions of PD. Therefore, alpha-synuclein plays an important role in the pathogenesis of familial and sporadic PD. To model alpha-synuclein-linked disease in vivo, transgenic mouse models have been developed that express wild-type or mutant human alpha-synuclein from a variety of neuronal-selective heterologous promoter elements. These models exhibit a variety of behavioral and neuropathological features resembling some aspects of PD. However, an important deficiency of these models is the observed lack of robust or progressive nigrostriatal dopaminergic neuronal degeneration that is characteristic of PD. RESULTS: We have developed conditional alpha-synuclein transgenic mice that can express A53T, E46K or C-terminally truncated (1-119) human alpha-synuclein pathological variants from the endogenous murine ROSA26 promoter in a Cre recombinase-dependent manner. Using these mice, we have evaluated the expression of these alpha-synuclein variants on the integrity and viability of nigral dopaminergic neurons with age. Expression of A53T alpha-synuclein or truncated alphaSyn119 selectively in nigrostriatal pathway dopaminergic neurons for up to 12 months fails to precipitate dopaminergic neuronal loss in these mice. However, alphaSyn119 expression in nigral dopaminergic neurons for up to 12 months causes a marked reduction in the levels of striatal dopamine and its metabolites together with other subtle neurochemical alterations. CONCLUSION: We have developed and evaluated novel conditional alpha-synuclein transgenic mice with transgene expression directed selectively to nigrostriatal dopaminergic neurons as a potential new mouse model of PD. Our data support the pathophysiological relevance of C-terminally truncated alpha-synuclein species in vivo. The expression of alphaSyn119 in the mouse nigrostriatal dopaminergic pathway may provide a useful model of striatal dopamine depletion and could potentially provide a presymptomatic model of PD perhaps representative of the earliest derangements in dopaminergic neuronal function observed prior to neuronal loss. These conditional alpha-synuclein transgenic mice provide novel tools for evaluating and dissecting the age-related effects of alpha-synuclein pathological variants on the function of the nigrostriatal dopaminergic pathway or other specific neuronal populations.

The identification of a caffeine-induced Ca2+ influx pathway in rat primary sensory neurons.

Caffeine-induced Ca2+ transients (CICTs) in rabbit nodose ganglion neurons (NGNs) are produced by two distinct mechanisms: release from intracellular stores via ryanodine receptors and Ca2+ influx across the plasma membrane, due to activation of an unknown receptor. In isolated rat NGNs, we used single-cell microfluorimetry to measure changes in intracellular Ca2+ and to test whether TRPV1 receptors underlie the Ca2+ influx pathway. Caffeine (10 mM) evoked CICTs in all NGNs tested (n = 47) averaging 365 +/- 32 nM. CICTs were partially dependent upon a Ca2+ influx pathway that ranged between 33% and 98% of the total Ca2+ transient. Application of two selective TRPV1 antagonists significantly attenuated CICTs. The peak average amplitudes of CICTs in Ca2+-free Locke solution and Ca2+-free Locke solution with IRTX or with BCTC were not significantly different from one another (n = 5 and 7, respectively). These observations suggest that caffeine can induce Ca2+ influx by activating TRPV1 channels.