Calcium homeostasis is a cellular process required for proper cell function and survival, maintained by the coordinated action of several transporters, among them members of the Na + /Ca 2+ -exchanger family, such as SLC8A3. Transforming growth factor beta (TGF-β) signaling defines neuronal development and survival and may regulate the expression of channels and transporters. We investigated the regulation of SLC8A3 by TGF-β in a conditional knockout mouse with deletion of TGF-β signaling from Engrailed 1-expressing cells, i.e., in cells from the midbrain and rhombomere 1, and elucidated the underlying molecular mechanisms. The results show that SLC8A3 is significantly downregulated in developing dopaminergic and dorsal raphe serotonergic neurons in mutants and that low SLC8A3 abundance prevents the expression of the anti-apoptotic protein Bcl-xL. TGF-β signaling affects SLC8A3 via the canonical and p38 signaling pathway and may increase the binding of Smad4 to the Slc8a3 promoter. Expression of the lipid peroxidation marker malondialdehyde (MDA) was increased following knockdown of Slc8a3 expression in vitro. In neurons lacking TGF-β signaling, the number of MDA-and 4-hydroxynonenal (4-HNE)-positive cells was significantly increased, accompanied with increased cellular 4-HNE abundance. These results suggest that TGF-β contributes to the regulation of SLC8A3 expression in developing dopaminergic and dorsal raphe serotonergic neurons, thereby preventing oxidative stress.Cellular ionic homeostasis is a prerequisite for proper cellular function and survival, whereby TGF-βs are known to regulate several channels and transporters within or outside the central nervous system [6][7][8][9]. Particularly, the link between TGF-βs and Ca 2+ homeostasis has been documented in several cellular paradigms: In cortical neurons, TGF-β regulates L-type Ca 2+ channels through MEK, JNK1/2, and p38 MAPK signaling [10]; it increases store-operated Ca 2+ entry into megakaryocytes [11]; and it enhances Ca 2+ influx pathways and the expression of transient receptor potential canonical channels (TRPCs) in human cardiac fibroblasts. Interestingly, human cardiac fibroblasts express several TRPC-mediated Ca 2+ influx pathways, which activate the reverse mode Na + /Ca 2+ exchanger (NCX) [12].Among the NCX isoformsSLC8A3), the isoform 3 of the Na + /Ca 2+ exchanger (NCX3), is exclusively expressed in excitable cells [13]. It mediates the electrogenic transport of Na + and Ca 2+ , and contributes to the maintenance of Ca 2+ homeostasis. SLC8A3 acts with a stoichiometry of 3:1 and may operate in the forward (Ca 2+ efflux) or reverse (influx of Ca 2+ ) mode. However, the forward mode is the predominant mode of Na + /Ca 2+ exchanger action. Alternative splicing generates two variants, AC and B, which display a tissue-specific distribution in mice. The variant B of Slc8a3 is mostly expressed in the brain, including substantia nigra pars compacta (SNc) and hindbrain raphe nuclei, whereas the variant AC is predominant in skeletal muscle. The function...
The K+/Cl‐ co‐transporter 2 (KCC2), a protein exclusively expressed in neurons, facilitates the co‐transport of a K+ and a Cl‐ ion across the cell membrane. The developmental shift of GABAA receptor mediated responses from depolarizing to hyperpolarizing is mainly due to a developmental upregulation of KCC2. Moreover, in mature neurons, neuronal activity leads to a decrease in surface expression and phosphorylation of Ser940 residue of KCC2, thereby reducing its activity. KCC2 is additionally phosphorylated at Thr906 and Thr1007, which reduces KCC2 surface expression and thus activity. Given the important role of neuronal activity in regulating KCC2 expression, we sought to investigate the effect of pilocarpine or 4‐aminopyridine (4AP) treatment on KCC2 expression across different maturation stages of neurons using quantitative RT‐PCR, immunocytochemistry (ICC) and immunoblotting. We also investigated the three phosphorylation sites – Ser940, Thr906 and Thr1007 – of KCC2. Immature neurons (day in vitro 4) from embryonic day 18.5 mouse hippocampus were treated with pilocarpine or 4AP (100µM, 60 minutes). The results show that 4AP or pilocarpine treatment has no effect on KCC2 transcript or protein expression, compared to controls. Similarly, ICC and immunoblotting results showed that there was no change in the phosphorylation status of Ser940. ICC results also showed that the phosphorylation status of Thr906 and Thr1007 remained unaltered in immature neurons after pilocarpine treatment. In day in vitro 17 organotypic hippocampal slices cultured from postnatal day 2 mouse pups, immunoblotting showed that treatment with 4AP did not affect KCC2 protein expression. However, in day in vitro 35 organotypic hippocampal slice cultures, 4AP treatment reduced KCC2 whole protein expression. These results demonstrate that neuronal activity has a distinctive effect on KCC2 protein as the neurons mature, suggesting a differential regulation of KCC2 protein at different maturation stages.
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