Channels formed by the transient receptor potential (TRP) family of proteins have a variety of physiological functions. Here we report that two members of the TRP cation channel (TRPC) subfamily, TRPC3 and 6, protected cerebellar granule neurons (CGNs) against serum deprivation-induced cell death in cultures and promoted CGN survival in rat brain. In CGN cultures, blocking TRPC channels or downregulating TRPC3 or 6 suppressed brain-derived neurotrophic factor (BDNF)-mediated protection, BDNF-triggered intracellular Ca2+ elevation and BDNF-induced CREB activation. By contrast, overexpressing TRPC3 or 6 increased CREB-dependent reporter gene transcription and prevented apoptosis in the neurons deprived of serum, and this protection was blocked by the dominant negative form of CREB. Furthermore, downregulating TRPC3 or 6 induced CGN apoptosis in neonatal rat cerebellum, and this effect was rescued by overexpressing either TRPC3 or 6. Thus, our findings provide in vitro and in vivo evidence that TRPC channels are important in promoting neuronal survival.

The transient receptor potential canonical (TRPC) channels are Ca2+-permeable, nonselective cation channels with different biological functions, but their roles in brain are largely unknown. Here we report that TRPC6 was localized to excitatory synapses and promoted their formation via a CaMKIV-CREB-dependent pathway. TRPC6 transgenic mice showed enhancement in spine formation, and spatial learning and memory in Morris water maze. These results reveal a previously unknown role of TRPC6 in synaptic and behavioral plasticity.

The canonical transient receptor potential channels (TRPCs) are Ca2+-permeable nonselective cation channels with various physiological functions. Here, we report that TRPC6, a member of the TRPC family, promotes hippocampal neuron dendritic growth. The peak expression of TRPC6 in rat hippocampus was between postnatal day 7 and 14, a period known to be important for maximal dendritic growth. Overexpression of TRPC6 increased phosphorylation of Ca2+/calmodulin-dependent kinase IV (CaMKIV) and cAMP-response-element binding protein (CREB) and promoted dendritic growth in hippocampal cultures. Downregulation of TRPC6 by short hairpin RNA interference against TRPC6 suppressed phosphorylation of both CaMKIV and CREB and impaired dendritic growth. Expressing a dominant-negative form of CaMKIV or CREB blocked the TRPC6-induced dendritic growth. Furthermore, inhibition of Ca2+ influx suppressed the TRPC6 effect on dendritic growth. Finally, in TRPC6 transgenic mice, the phosphorylation of CaMKIV and CREB was enhanced and the dendritic growth was also increased. In conclusion, TRPC6 promoted dendritic growth via the CaMKIV-CREB pathway. Our results thus revealed a novel role of TRPC6 during the development of the central nervous system (CNS).

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Graphical Abstract Highlights d NF186 is dispensable for neocortical PyN AIS innervation by ChCs d Postsynaptic PyN-expressed L1CAM regulates PyN AIS synaptic innervation by ChCs d L1CAM is required for the establishment and maintenance of ChC/PyN AIS innervation d AnkG-mediated L1CAM anchoring at the AIS is necessary for ChC/PyN AIS innervation SUMMARY Among the diverse interneuron subtypes in the neocortex, chandelier cells (ChCs) are the only population that selectively innervate pyramidal neurons (PyNs) at their axon initial segment (AIS), the site of action potential initiation, allowing them to exert powerful control over PyN output. Yet, mechanisms underlying their subcellular innervation of PyN AISs are unknown. To identify molecular determinants of ChC/PyN AIS innervation, we performed an in vivo RNAi screen of PyN-expressed axonal cell adhesion molecules (CAMs) and select Ephs/ephrins. Strikingly, we found the L1 family member L1CAM to be the only molecule required for ChC/PyN AIS innervation. Further, we show that L1CAM is required during both the establishment and maintenance of innervation, and that selective innervation of PyN AISs by ChCs requires AIS anchoring of L1CAM by the cytoskeletal ankyrin-G/bIV-spectrin complex. Thus, our findings identify PyN-expressed L1CAM as a critical CAM required for innervation of neocortical PyN AISs by ChCs.

Mitochondrial Ca2+ homeostasis is fundamental to regulation of mitochondrial membrane potential, ATP production, and cellular Ca 2+ homeostasis. It has been known for decades that isolated mitochondria can take up Ca 2+ from the extramitochondrial solution, but the molecular identity of the Ca 2+ channels involved in this action is largely unknown. Here, we show that a fraction of canonical transient receptor potential 3 (TRPC3) channels is localized to mitochondria, a significant fraction of mitochondrial Ca 2+ uptake that relies on extramitochondrial Ca 2+ concentration is TRPC3-dependent, and the up-and down-regulation of TRPC3 expression in the cell influences the mitochondrial membrane potential. Our findings suggest that TRPC3 channels contribute to mitochondrial Ca 2+ uptake. We anticipate our observations may provide insights into the mechanisms of mitochondrial Ca 2+ uptake and advance understanding of the physiological role of TRPC3.

The mechanisms by which TGF-b promotes lung adenocarcinoma (ADC) metastasis are largely unknown. Here, we report that in lung ADC cells, TGF-b potently induces expression of DOCK4, but not other DOCK family members, via the Smad pathway and that DOCK4 induction mediates TGF-b's prometastatic effects by enhancing tumor cell extravasation. TGF-b-induced DOCK4 stimulates lung ADC cell protrusion, motility, and invasion without affecting epithelial-to-mesenchymal transition. These processes, which are fundamental to tumor cell extravasation, are driven by DOCK4-mediated Rac1 activation, unveiling a novel link between TGF-b and Rac1. Thus, our findings uncover the atypical Rac1 activator DOCK4 as a key component of the TGF-b/Smad pathway that promotes lung ADC cell extravasation and metastasis.

Summary Chandelier cells (ChCs), typified by their unique axonal morphology, are the most distinct interneurons present in cortical circuits. Via their distinctive axonal terminals, called cartridges, these cells selectively target the axon initial segment of pyramidal cells and control action potential initiation; yet, the mechanisms that govern the characteristic ChC axonal structure have remained elusive. Here, by employing an in utero electroporation-based method that enables genetic labeling and manipulation of ChCs in vivo, we identify DOCK7, a member of the DOCK180 family, as a molecule essential for ChC cartridge/bouton development. We further present evidence that DOCK7 functions as a cytoplasmic activator of the schizophrenia-associated ErbB4 receptor tyrosine kinase, and that DOCK7 modulates ErbB4 activity to control ChC cartridge/bouton development. Thus, our findings define DOCK7 and ErbB4 as key components of a pathway that controls the morphological differentiation of ChCs, with implications for the pathogenesis of schizophrenia.