Cytoplasmic BK\u3csub\u3eCa\u3c/sub\u3e channel intron-containing mRNAs contribute to the intrinsic excitability of hippocampal neurons

High single-channel conductance K+ channels, which respond jointly to membrane depolarization and micromolar concentrations of intracellular Ca2+ ions, arise from extensive cell-specific alternative splicing of pore-forming α-subunit mRNAs. Here, we report the discovery of an endogenous BKCa channel α-subunit intron-containing mRNA in the cytoplasm of hippocampal neurons. This partially processed mRNA, which comprises ≈10% of the total BKCa channel α-subunit mRNAs, is distributed in a gradient throughout the somatodendritic space. We selectively reduced endogenous cytoplasmic levels of this intron-containing transcript by RNA interference without altering levels of the mature splice forms of the BKCa channel mRNAs. In doing so, we could demonstrate that changes in a unique BKCa channel α-subunit introncontaining splice variant mRNA can greatly impact the distribution of the BKCa channel protein to dendritic spines and intrinsic firing properties of hippocampal neurons. These data suggest a new regulatory mechanism for modulating the membrane properties and ion channel gradients of hippocampal neurons

HDAC6 Regulates Glucocorticoid Receptor Signaling in Serotonin Pathways with Critical Impact on Stress Resilience

Genetic variations in certain components of the glucocorticoid receptor (GR) chaperone complex have been associated with the development of stress-related affective disorders and individual variability in therapeutic responses to antidepressants. Mechanisms that link GR chaperoning and stress susceptibility are not well understood. Here, we show that the effects of glucocorticoid hormones on socioaffective behaviors are critically regulated via reversible acetylation of Hsp90, a key component of the GR chaperone complex. We provide pharmacological and genetic evidence indicating that the cytoplasmic lysine deacetylase HDAC6 controls Hsp90 acetylation in the brain, and thereby modulates Hsp90–GR protein–protein interactions, as well as hormone- and stress-induced GR translocation, with a critical impact on GR downstream signaling and behavior. Pet1-Cre-driven deletion of HDAC6 in serotonin neurons, the densest HDAC6-expressing cell group in the mouse brain, dramatically reduced acute anxiogenic effects of the glucocorticoid hormone corticosterone in the open-field, elevated plus maze, and social interaction tests. Serotonin-selective depletion of HDAC6 also blocked the expression of social avoidance in mice exposed to chronic social defeat and concurrently prevented the electrophysiological and morphological changes induced, in serotonin neurons, by this murine model of traumatic stress. Together, these results identify HDAC6 inhibition as a potential new strategy for proresilience and antidepressant interventions through regulation of the Hsp90–GR heterocomplex and focal prevention of GR signaling in serotonin pathways. Our data thus uncover an alternate mechanism by which pan-HDAC inhibitors may regulate stress-related behaviors independently of their action on histones

HDAC6-mediated effects in mouse models of stress and depression

Recent preclinical studies indicate that loss of HDAC6 function promotes stress resilience and induces antidepressant-like responses in rodents. Although these results point to HDAC6 inhibition as a potential mechanism for the treatment of neuropsychiatric conditions, in vivo pharmacological target validation has been hampered by lack of isoform selectivity and poor brain bioavailability of current probes. Additionally, as more targets of HDAC6 are found, the downstream mechanisms that mediate this activity remain poorly understood. This work validates the behavioral activity of two novel pyrimidine hydroxyl amide small molecules with high selectivity for HDAC6 and improved brain bioavailability in a number of mouse models of stress and depression and explores some potential downstream mechanisms. Data here shows that ACY-738 and ACY-775 led to anxiolytic effects in the open-field, marble burying and novelty induced hypophagia tests, and antidepressant-like effects in tail suspension test and following chronic social defeat stress. Hsp90, a known substrate of HDAC6, plays a key role in stress regulation through its function as a chaperone of the glucocorticoid receptor (GR) and its acetylation status regulates downstream hormone signaling via GR, but the contribution of this molecular mechanism in stress homeostasis has not been clearly elucidated. This study shows that acetylation of Hsp90 is differentially regulated in mice that are spontaneously resilient to developing a depressive-like phenotype and this led to differences in association with GR and other co-chaperones, and alters GR trafficking into the nucleus. Additionally, the direct contribution of this acetylation is investigated using viral-mediated expression of acetylation mimic mutant of Hsp90 in the serotonin system. Overexpression of this acetyl mimic leads to an antidepressant-like phenotype compared to mice expressing control virus and has similar effects to HDAC6 loss of function on GR chaperone complex and trafficking. This work also begins to explore the effects of HDAC6 loss of function on the neuroplastic effects that could be related to its antidepressant-like effect. The results presented here validate new isoform-selective probes for pharmacological inhibition of HDAC6 in the CNS, highlight the likely involvement of Hsp90 hyperacetylation in the antidepressant response to HDAC6 inhibition, and serve as proof of principle that HDAC6 could be a valid target for antidepressant development

Melanocyte-like cells in the heart and pulmonary veins contribute to atrial arrhythmia triggers

Atrial fibrillation is the most common clinical cardiac arrhythmia. It is often initiated by ectopic beats arising from the pulmonary veins and atrium, but the source and mechanism of these beats remains unclear. The melanin synthesis enzyme dopachrome tautomerase (DCT) is involved in intracellular calcium and reactive species regulation in melanocytes. Given that dysregulation of intracellular calcium and reactive species has been described in patients with atrial fibrillation, we investigated the role of DCT in this process. Here, we characterize a unique DCT-expressing cell population within murine and human hearts that populated the pulmonary veins, atria, and atrioventricular canal. Expression profiling demonstrated that this population expressed adrenergic and muscarinic receptors and displayed transcriptional profiles distinct from dermal melanocytes. Adult mice lacking DCT displayed normal cardiac development but an increased susceptibility to atrial arrhythmias. Cultured primary cardiac melanocyte-like cells were excitable, and those lacking DCT displayed prolonged repolarization with early afterdepolarizations. Furthermore, mice with mutations in the tyrosine kinase receptor Kit lacked cardiac melanocyte-like cells and did not develop atrial arrhythmias in the absence of DCT. These data suggest that dysfunction of melanocyte-like cells in the atrium and pulmonary veins may contribute to atrial arrhythmias