Rabconnectin-3α/DMXL2 Is Locally Enriched at the Synaptic Ribbon of Rod Photoreceptor Synapses.

Ribbon synapses reliably transmit synaptic signals over a broad signalling range. Rod photoreceptor ribbon synapses are capable of transmitting signals generated by the absorption of single photons. The high precision of ribbon synapses emphasizes the need for particularly efficient signalling mechanisms. Synaptic ribbons are presynaptic specializations of ribbon synapses and are anchored to the active zone. Synaptic ribbons bind many synaptic vesicles that are delivered to the active zone for continuous and faithful signalling. In the present study we demonstrate with independent antibodies at the light- and electron microscopic level that rabconnectin-3α (RC3α)-alternative name Dmx-like 2 (DMXL2)-is localized to the synaptic ribbons of rod photoreceptor synapses in the mouse retina. In the brain, RC3α-containing complexes are known to interact with important components of synaptic vesicles, including Rab3-activating/inactivating enzymes, priming proteins and the vesicular H+-ATPase that acidifies the synaptic vesicle lumen to promote full neurotransmitter loading. The association of RC3α/DMXL2 with rod synaptic ribbons of the mouse retina could enable these structures to deliver only fully signalling-competent synaptic vesicles to the active zone thus contributing to reliable synaptic communication.

CAPN1 (Calpain1)-Dependent Cleavage of STIM1 (Stromal Interaction Molecule 1) Results in an Enhanced SOCE (Store-Operated Calcium Entry) in Human Neonatal Platelets.

BACKGROUND: Altered intracellular Ca2+ homeostasis in neonatal platelets has been previously reported. This study aims to examine the changes in the Ca2+ entry through the store-operated calcium entry (SOCE) mechanism in neonatal platelets. METHODS: Human platelets from either control women, mothers, and neonates were isolated and, following, were fixed after being treated as required. Platelet samples were analyzed by Western blotting, qRT-PCR, and MALDITOF/TOF. Ca2+ homeostasis was also determined. Culture cells were used as surrogated of platelets to overexpress the proteins of interest to reproduce the alterations observed in platelets. RESULTS: Altered TG (thapsigargin)-evoked SOCE, alternative molecular weight form of STIM1 (stromal interaction molecule 1; s-STIM1 [short STIM1 isoform (478 aa)], around 60 kDa) and overexpression of SARAF (SOCE-associated regulatory factor) were found in neonatal platelets as compared to maternal and control women platelets. s-STIM1 may result due to CAPN1 (calpain1)-dependent processing, as confirmed in platelets and MEG01 cells by using calpeptin and overexpressing CAPN1, respectively. In HEK293 (STIM1 and STIM2 [stromal interaction molecule 2] double knockout) cells transfected either with c-STIM1 (canonical STIM1 [685 aa]), s-STIM1 (478), STIM1B (540), and CAPN1 overexpression plasmids, we found s-STIM1 and c-STIM1, except in cells overexpressing s-STIM1 (478) that lacked CAPN1 target residues. These results and the in silico analysis, lead us to conclude that STIM1 is cleaved at Q496 by CAPN1. Ca2+ imaging analysis and coimmunoprecipitation assay using MEG01 and HEK293 cells overexpressing SARAF together with s-STIM1 (478) reported a reduced slow Ca2+-dependent inactivation, so reproducing the Ca2+-homeostasis pattern observed in neonatal platelets. CONCLUSIONS: CAPN1 may cleave STIM1 in neonatal platelets, hence, impairing SARAF coupling after SOCE activation. s-STIM1 may avoid slow Ca2+-dependent inactivation and, subsequently, results in an enhanced TG-evoked SOCE as observed in neonatal platelets.

Effects of Telmisartan, an AT1 receptor antagonist, on mitochondria-specific genes expression in a mouse MPTP model of Parkinsonism.

Background: Mitochondrial dysfunction plays a crucial role in Parkinson's disease (PD) pathogenesis. The present study was undertaken to investigate the effects of Telmisartan (TEL), an angiotensin II type 1 receptor (AT1R) blocker, on the mitochondria-specific genes expression in a mouse model of Parkinsonism. Materials and methods: Mice were divided into 5 groups with 6 in each; Group I received 0.5% CMC (control) + saline, Group II received 0.5% CMC + 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (positive control), Group III & IV received MPTP + TEL 3 and 10 mg/kg, p.o. respectively, Group V received TEL 10 mg/kg, p.o. (drug control). MPTP was given 80 mg/kg intraperitoneal in two divided doses (40 mg/kg × 2 at 16 h time interval). Vehicle or TEL was administered 1 h before the MPTP injection. Motor function was assessed 48 h after the first dose of MPTP and animals were euthanized to collect brain. Results: Mice intoxicated with MPTP showed locomotor deficits and significant upregulation of α-synuclein (α-syn), downregulation of metastasis-associated protein 1 (MTA1), and Ubiquitin C-terminal hydrolase L1 (UCHL1) in the substantia nigra pars compacta (SNpc) and Striatum (STr) regions of brains. In addition, MPTP intoxication down-regulated mitochondria-specific genes such as DJ-1, PTEN-induced putative kinase 1 (PINK1), Parkin, enriched with leucine repeats kinase 2 (LRRK2) gene expfression. Pre-treatment with TEL restored locomotor functions and upregulated PINK1, Parkin, LRRK2, DJ-1, MTA1 and UCHL1. Conclusion: The present study evidences that TEL has the ability to improve mitochondrial functions in PD.

A short isoform of STIM1 confers frequency-dependent synaptic enhancement.

Store-operated Ca2+-entry (SOCE) regulates basal and receptor-triggered Ca2+ signaling with STIM proteins sensing the endoplasmic reticulum (ER) Ca2+ content and triggering Ca2+ entry by gating Orai channels. Although crucial for immune cells, STIM1's role in neuronal Ca2+ homeostasis is controversial. Here, we characterize a splice variant, STIM1B, which shows exclusive neuronal expression and protein content surpassing conventional STIM1 in cerebellum and of significant abundance in other brain regions. STIM1B expression results in a truncated protein with slower kinetics of ER-plasma membrane (PM) cluster formation and ICRAC, as well as reduced inactivation. In primary wild-type neurons, STIM1B is targeted by its spliced-in domain B to presynaptic sites where it converts classic synaptic depression into Ca2+- and Orai-dependent short-term synaptic enhancement (STE) at high-frequency stimulation (HFS). In conjunction with altered STIM1 splicing in human Alzheimer disease, our findings highlight STIM1 splicing as an important regulator of neuronal calcium homeostasis and of synaptic plasticity.