Cacna1c in the Prefrontal Cortex Regulates Depression-Related Behaviors via REDD1.

The CACNA1C gene that encodes the L-type Ca2+ channel (LTCC) Cav1.2 subunit has emerged as a candidate risk gene for multiple neuropsychiatric disorders including bipolar disorder, major depressive disorder, and schizophrenia, all marked with depression-related symptoms. Although cacna1c heterozygous (HET) mice have been previously reported to exhibit an antidepressant-like phenotype, the molecular and circuit-level dysfunction remains unknown. Here we report that viral vector-mediated deletion of cacna1c in the adult prefrontal cortex (PFC) of mice recapitulates the antidepressant-like effect observed in cacna1c HET mice using the sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST). Molecular studies identified lower levels of REDD1, a protein previously linked to depression, in the PFC of HET mice, and viral-mediated REDD1 overexpression in the PFC of these HET mice reversed the antidepressant-like effect in SPT and TST. Examination of downstream REDD1 targets found lower levels of active/phosphorylated Akt (S473) with no change in mTORC1 phosphorylation. Examination of the transcription factor FoxO3a, previously linked to depression-related behavior and shown to be regulated in other systems by Akt, revealed higher nuclear levels in the PFC of cacna1c HET mice that was further increased following REDD1-mediated reversal of the antidepressant-like phenotype. Collectively, these findings suggest that REDD1 in cacna1c HET mice may influence depression-related behavior via regulation of the FoxO3a pathway. Cacna1c HET mice thus serve as a useful mouse model to further study cacna1c-associated molecular signaling and depression-related behaviors relevant to human CACNA1C genetic variants.

Psychological Stress Activates the Inflammasome via Release of Adenosine Triphosphate and Stimulation of the Purinergic Type 2X7 Receptor.

BACKGROUND: The mechanisms underlying stress-induced inflammation that contribute to major depressive disorder are unknown. We examine the role of the adenosine triphosphate (ATP)/purinergic type 2X7 receptor (P2X7R) pathway and the NLRP3 (nucleotide-binding, leucine-rich repeat, pyrin domain containing 3) inflammasome in interleukin (IL)-1ß and depressive behavioral responses to stress. METHODS: The influence of acute restraint stress on extracellular ATP, glutamate, IL-1ß, and tumor necrosis factor alpha in hippocampus was determined by microdialysis, and the influence of acute restraint stress on the NLRP3 inflammasome was determined by western blot analysis. The influence of P2X7R antagonist administration on IL-1ß and tumor necrosis factor alpha and on anxiety and depressive behaviors was determined in the chronic unpredictable stress rodent model. The role of the NLRP3 inflammasome was determined by analysis of Nlrp3 null mice. RESULTS: Acute restraint stress rapidly increased extracellular ATP, an endogenous agonist of P2X7R; the inflammatory cytokine IL-1ß; and the active form of the NLRP3 inflammasome in the hippocampus. Administration of a P2X7R antagonist completely blocked the release of IL-1ß and tumor necrosis factor alpha, another stress-induced cytokine, and activated NLRP3. Moreover, P2X7R antagonist administration reversed the anhedonic and anxiety behaviors caused by chronic unpredictable stress exposure, and deletion of the Nlrp3 gene rendered mice resistant to development of depressive behaviors caused by chronic unpredictable stress. CONCLUSIONS: These findings demonstrate that psychological "stress" is sensed by the innate immune system in the brain via the ATP/P2X7R-NLRP3 inflammasome cascade, and they identify novel therapeutic targets for the treatment of stress-related mood disorders and comorbid illnesses.

Rapid antidepressant actions of scopolamine: Role of medial prefrontal cortex and M1-subtype muscarinic acetylcholine receptors.

Clinical studies demonstrate that scopolamine, a non-selective muscarinic acetylcholine receptor (mAchR) antagonist, produces rapid therapeutic effects in depressed patients, and preclinical studies report that the actions of scopolamine require glutamate receptor activation and the mechanistic target of rapamycin complex 1 (mTORC1). The present study extends these findings to determine the role of the medial prefrontal cortex (mPFC) and specific muscarinic acetylcholine receptor (M-AchR) subtypes in the actions of scopolamine. The administration of scopolamine increases the activity marker Fos in the mPFC, including the infralimbic (IL) and prelimbic (PrL) subregions. Microinfusions of scopolamine into either the IL or the PrL produced significant antidepressant responses in the forced swim test, and neuronal silencing of IL or PrL blocked the antidepressant effects of systemic scopolamine. The results also demonstrate that the systemic administration of a selective M1-AChR antagonist, VU0255035, produced an antidepressant response and stimulated mTORC1 signaling in the PFC, similar to the actions of scopolamine. Finally, we used a chronic unpredictable stress model as a more rigorous test of rapid antidepressant actions and found that a single dose of scopolamine or VU0255035 blocked the anhedonic response caused by CUS, an effect that requires the chronic administration of typical antidepressants. Taken together, these findings indicate that mPFC is a critical mediator of the behavioral actions of scopolamine and identify the M1-AChR as a therapeutic target for the development of novel and selective rapid-acting antidepressants.

Dysregulated intracellular signaling in the striatum in a pathophysiologically grounded model of Tourette syndrome.

Tic disorders produce substantial morbidity, but their pathophysiology remains poorly understood. Convergent evidence suggests that dysregulation of the cortico-basal ganglia circuitry is central to the pathogenesis of tics. Tourette syndrome (TS), the most severe end of the continuum of tic disorders, is substantially genetic, but causative mutations have been elusive. We recently described a mouse model, the histidine decarboxylase (Hdc) knockout mouse, that recapitulates a rare, highly penetrant mutation found in a single family; these mice exhibit TS-like phenomenology. These animals have a global deficit in brain histamine and a consequent dysregulation of DA in the basal ganglia. Histamine modulation of DA effects is increasingly appreciated, but the mechanisms underlying this modulation remain unclear; the consequences of modest DA elevation in the context of profound HA deficiency are difficult to predict, but understanding them in the Hdc knockout mouse may provide generalizable insights into the pathophysiology of TS. Here we characterized signaling pathways in striatal cells in this model system, at baseline and after amphetamine challenge. In vivo microdialysis confirms elevated DA in Hdc-KO mice. We find dephosphorylation of Akt and its target GSK3ß and activation of the MAPK signaling cascade and its target rpS6; these are characteristic of the effects of DA on D2- and D1-expressing striatal neurons, respectively. Strikingly, there is no alteration in mTOR signaling, which can be regulated by DA in both cell types. These cellular effects help elucidate striatal signaling abnormalities in a uniquely validated mouse model of TS and move towards the identification of new potential therapeutic targets for tic disorders.

Activity-dependent p25 generation regulates synaptic plasticity and Aß-induced cognitive impairment.

Cyclin-dependent kinase 5 regulates numerous neuronal functions with its activator, p35. Under neurotoxic conditions, p35 undergoes proteolytic cleavage to liberate p25, which has been implicated in various neurodegenerative diseases. Here, we show that p25 is generated following neuronal activity under physiological conditions in a GluN2B- and CaMKIIα-dependent manner. Moreover, we developed a knockin mouse model in which endogenous p35 is replaced with a calpain-resistant mutant p35 (Δp35KI) to prevent p25 generation. The Δp35KI mice exhibit impaired long-term depression and defective memory extinction, likely mediated through persistent GluA1 phosphorylation at Ser845. Finally, crossing the Δp35KI mice with the 5XFAD mouse model of Alzheimer's disease (AD) resulted in an amelioration of ß-amyloid (Aß)-induced synaptic depression and cognitive impairment. Together, these results reveal a physiological role of p25 production in synaptic plasticity and memory and provide new insights into the function of p25 in Aß-associated neurotoxicity and AD-like pathology.

A dietary regimen of caloric restriction or pharmacological activation of SIRT1 to delay the onset of neurodegeneration.

Caloric restriction (CR) is a dietary regimen known to promote lifespan by slowing down the occurrence of age-dependent diseases. The greatest risk factor for neurodegeneration in the brain is age, from which follows that CR might also attenuate the progressive loss of neurons that is often associated with impaired cognitive capacities. In this study, we used a transgenic mouse model that allows for a temporally and spatially controlled onset of neurodegeneration to test the potentially beneficial effects of CR. We found that in this model, CR significantly delayed the onset of neurodegeneration and synaptic loss and dysfunction, and thereby preserved cognitive capacities. Mechanistically, CR induced the expression of the known lifespan-regulating protein SIRT1, prompting us to test whether a pharmacological activation of SIRT1 might recapitulate CR. We found that oral administration of a SIRT1-activating compound essentially replicated the beneficial effects of CR. Thus, SIRT1-activating compounds might provide a pharmacological alternative to the regimen of CR against neurodegeneration and its associated ailments.