Abstract
Calcium-dependent secretion activator 2 (CAPS2) regulates the trafficking and exocytosis of neuropeptide-containing dense-core vesicles (DCVs). CAPS2 is prominently expressed in the medial habenula (MHb), which is related to depressive behavior; however, how MHb neurons cause depressive symptoms and the role of CAPS2 remains unclear. We hypothesized that dysfunction of MHb CAPS neurons might cause defects in neuropeptide secretion and the activity of monoaminergic centers, resulting in depressive-like behaviors. In this study, we examined (1) CAPS2 expression in the habenula of depression animal models and major depressive disorder patients and (2) the effects of down-regulation of MHb CAPS2 on the animal behaviors, synaptic transmission in the interpeduncular nucleus (IPN), and neuronal activity of monoamine centers. Habenular CAPS2 expression was decreased in the rat chronic restraint stress model, mouse learned helplessness model, and showed tendency to decrease in depression patients who died by suicide. Knockdown of CAPS2 in the mouse habenula evoked despair-like behavior and a reduction of the release of DCVs in the IPN. Neuronal activity of IPN and monoaminergic centers was also reduced. These results implicate MHb CAPS2 as playing a pivotal role in depressive behavior through the regulation of neuropeptide secretion of the MHb-IPN pathway and the activity of monoaminergic centers.
Highlights
Calcium-dependent secretion activator 2 (CAPS2) regulates the trafficking and exocytosis of neuropeptide-containing dense-core vesicles (DCVs)
We found that CAPS2 mRNA expression was significantly reduced in the habenula of chronic restraint stress (CRS) rats compared with those of non-stressed (NS) rats (n = 4 for each group, Mann–Whitney U-test; NS vs. CRS expressed as fold change: 1.00 ± 0.14 vs. 0.61 ± 0.09, P = 0.029; Fig. 1a) and CAPS2 protein levels in the interpeduncular nucleus (IPN), a direct downstream of the medial habenula (MHb), showed a tendency to decrease, being 53.8% of control, as shown via Western blotting (Supplementary Figure S1)
CAPS2 mRNA level was decreased in mice exposed to inescapable electric foot shocks inducing learned helplessness (LH) as compared with control mice (n = 6 for each group, Student’s t-test; control with empty target sequence (CON) vs. LH expressed as fold change: 1.00 ± 0.46 vs. 0.52 ± 0.38, T(14) = 2.285, P = 0.038; Fig. 1b)
Summary
Calcium-dependent secretion activator 2 (CAPS2) regulates the trafficking and exocytosis of neuropeptide-containing dense-core vesicles (DCVs). We hypothesized that dysfunction of MHb CAPS neurons might cause defects in neuropeptide secretion and the activity of monoaminergic centers, resulting in depressive-like behaviors. We examined (1) CAPS2 expression in the habenula of depression animal models and major depressive disorder patients and (2) the effects of down-regulation of MHb CAPS2 on the animal behaviors, synaptic transmission in the interpeduncular nucleus (IPN), and neuronal activity of monoamine centers. Neuronal activity of IPN and monoaminergic centers was reduced These results implicate MHb CAPS2 as playing a pivotal role in depressive behavior through the regulation of neuropeptide secretion of the MHb-IPN pathway and the activity of monoaminergic centers. The MHb contains numerous neuropeptides such as tachykinins, VGF, neuropeptide Y, and secretogranin 1–320, and CAPS2 is expressed in both MHbD and M HbV5,6,21 In this setting, CAPS2 may play a pivotal role in secretion of MHb neuropeptides
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