Individuals with Parkinson's disease (PD) experience a progressive decline in motor function as a result of selective loss of dopaminergic (DA) neurons in the substantia nigra. The mechanism(s) underlying the loss of DA neurons is not known. Here, we show that a neurotoxin that causes a disease that mimics PD upon administration to mice, because it induces the selective loss of DA neurons in the substantia nigra, alters Ca 2+ homeostasis and induces ER stress. In a human neuroblastoma cell line, we found that endogenous store-operated Ca 2+ entry (SOCE), which is critical for maintaining ER Ca 2+ levels, is dependent on transient receptor potential channel 1 (TRPC1) activity. Neurotoxin treatment decreased TRPC1 expression, TRPC1 interaction with the SOCE modulator stromal interaction molecule 1 (STIM1), and Ca 2+ entry into the cells. Overexpression of functional TRPC1 protected against neurotoxin-induced loss of SOCE, the associated decrease in ER Ca 2+ levels, and the resultant unfolded protein response (UPR). In contrast, silencing of TRPC1 or STIM1 increased the UPR. Furthermore, Ca 2+ entry via TRPC1 activated the AKT pathway, which has a known role in neuroprotection. Consistent with these in vitro data, Trpc1 -/-mice had an increased UPR and a reduced number of DA neurons. Brain lysates of patients with PD also showed an increased UPR and decreased TRPC1 levels. Importantly, overexpression of TRPC1 in mice restored AKT/mTOR signaling and increased DA neuron survival following neurotoxin administration. Overall, these results suggest that TRPC1 is involved in regulating Ca 2+ homeostasis and inhibiting the UPR and thus contributes to neuronal survival.

In neurons, Ca is essential for a variety of physiological processes that regulate gene transcription to neuronal growth and their survival. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridinium ions (MPP) are potent neurotoxins that selectively destroys the dopaminergic (DA) neurons and mimics Parkinson's disease (PD) like symptoms, but the mechanism as how MPP/MPTP effects DA neuron survival is not well-understood. In the present study, we found that MPP treatment increased the level of reactive oxygen species (ROS) that activates and upregulates the expression and function of melastatin-like transient receptor potential (TRPM) subfamily member, melastatin-like transient receptor potential channel 2 (TRPM2). Correspondingly, TRPM2 expression was also increased in substantia nigra of MPTP-induced PD mouse model and PD patients. ROS-mediated activation of TRPM2 resulted in an increased intracellular Ca, which in turn promoted cell death in SH-SY5Y cells. Intracellular Ca overload caused by MPP-induced ROS also affected calpain activity, followed by increased caspase 3 activities and activation of downstream apoptotic pathway. On the other hand, quenching of HO by antioxidants, resveratrol (RSV), or N-acetylcysteine (NAC) effectively blocked TRPM2-mediated Ca influx, decreased intracellular Ca overload, and increased cell survival. Importantly, pharmacological inhibition of TRPM2 or knockdown of TRPM2 using siRNA, but not control siRNA, showed an increased protection by preventing MPP-induced Ca increase and inhibited apoptosis. Taken together, we show here a novel role for TRPM2 expression and function in MPP-induced dopaminergic neuronal cell death.

Loss of dopaminergic (DA) neurons leads to Parkinson's disease; however, the mechanism(s) for the vulnerability of DA neurons is(are) not fully understood. We demonstrate that TRPC1 regulates the L-type Ca channel that contributes to the rhythmic activity of adult DA neurons in the substantia nigra region. Store depletion that activates TRPC1, via STIM1, inhibits the frequency and amplitude of the rhythmic activity in DA neurons of wild-type, but not in TRPC1, mice. Similarly, TRPC1 substantia nigra neurons showed increased L-type Ca currents, decreased stimulation-dependent STIM1-Ca1.3 interaction, and decreased DA neurons. L-type Ca currents and the open channel probability of Ca1.3 channels were also reduced upon TRPC1 activation, whereas increased Ca1.3 currents were observed upon STIM1 or TRPC1 silencing. Increased interaction between Ca1.3-TRPC1-STIM1 was observed upon store depletion and the loss of either TRPC1 or STIM1 led to DA cell death, which was prevented by inhibiting L-type Ca channels. Neurotoxins that mimic Parkinson's disease increased Ca1.3 function, decreased TRPC1 expression, inhibited Tg-mediated STIM1-Ca1.3 interaction, and induced caspase activation. Importantly, restoration of TRPC1 expression not only inhibited Ca1.3 function but increased cell survival. Together, we provide evidence that TRPC1 suppresses Ca1.3 activity by providing an STIM1-based scaffold, which is essential for DA neuron survival. Ca entry serves critical cellular functions in virtually every cell type, and appropriate regulation of Ca in neurons is essential for proper function. In Parkinson's disease, DA neurons are specifically degenerated, but the mechanism is not known. Unlike other neurons, DA neurons depend on Ca1.3 channels for their rhythmic activity. Our studies show that, in normal conditions, the pacemaking activity in DA neurons is inhibited by the TRPC1-STIM1 complex. Neurotoxins that mimic Parkinson's disease target TRPC1 expression, which leads to an abnormal increase in Ca1.3 activity, thereby causing degeneration of DA neurons. These findings link TRPC1 to Ca1.3 regulation and provide important indications about how disrupting Ca balance could have a direct implication in the treatment of Parkinson's patients.

Arginine vasopressin (AVP) is a hormone exerting vasoconstrictive and antidiuretic action in the periphery and serves as a neuromodulator in the brain. Although the hippocampus receives vasopressinergic innervation and AVP has been shown to facilitate the excitability of CA1 pyramidal neurons, the involved ionic and signaling mechanisms have not been determined. Here we found that AVP excited CA1

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