Regulation of Early Neurite Morphogenesis by the Na+/H+ Exchanger NHE1

Abstract

The ubiquitously expressed Na ϩ /H ϩ exchanger NHE1 plays an important role in regulating polarized membrane protrusion and directional motility in non-neuronal cells. Using NGF-differentiated PC12 cells and murine neocortical neurons in vitro, we now show that NHE1 plays a role in regulating early neurite morphogenesis. NHE1 was expressed in growth cones in which it gave rise to an elevated intracellular pH in actively extending neurites. The NHE1 inhibitor cariporide reversibly reduced growth cone filopodia number and the formation and elongation of neurites, especially branches, whereas the transient overexpression of full-length NHE1, but not NHE1 mutants deficient in either ion translocation activity or actin cytoskeletal anchoring, elicited opposite effects. In addition, compared with neocortical neurons obtained from wild-type littermates, neurons isolated from NHE1-null mice exhibited reductions in early neurite outgrowth, an effect that was rescued by overexpression of full-length NHE1 but not NHE1 mutants. Finally, the growth-promoting effects of netrin-1, but not BDNF or IGF-1, were markedly reduced by cariporide in wild-type neocortical neurons and were not observed in NHE1-null neurons. Although netrin-1 failed to increase growth cone intracellular pH or Na ϩ /H ϩ exchange activity, netrin-1-induced increases in early neurite outgrowth were restored in NHE1-null neurons transfected with full-length NHE1 but not an ion translocation-deficient mutant. Collectively, the results indicate that NHE1 participates in the regulation of early neurite morphogenesis and identify a novel role for NHE1 in the promotion of early neurite outgrowth by netrin-1.

Endosomal acidification by Na+/H+exchanger NHE5 regulates TrkA cell-surface targeting and NGF-induced PI3K signaling

“…Of interest, shNHE1 cells showed a small but significant increase in the number of cells forming neurites (Figure 8, A and C), a trend opposite to that observed in shNHE5 cells. However, in shNHE1 cells that did form neurites, the mean total neurite number and length were significantly reduced (Figure 8, A–D), in agreement with our previous study showing that pharmacological inhibition or genetic ablation of NHE1 adversely affect neurite elongation and branching (Sin et al. , 2009).…”

The role of intracellular sodium (Na+) in the regulation of calcium (Ca2+)-mediated signaling and toxicity

“…Previous studies have shown that Na + entry may cause an increase in cytosolic Ca 2+ through either Na + /Ca 2+ exchangers or activation of voltage-gated Ca 2+ channels 17,53, thereby activating Ca 2+ -dependent signaling mechanisms. Moreover, Na + entry via Na + /H + exchange may cause changes in intracellular pH, and thereby regulate many cellular functions including enzyme activity, neuronal growth and death 10,18,70,71,88,89. A recent study showed that Na + influx plays an important role in the onset of anti-Fas-induced apoptosis and that blocking Na + influx may rescue programmed cell death in Jurkat cells 19.…”

Ion imaging during axolotl tail regeneration in vivo

“…In axolotl oocytes, a flow of H þ has been measured which constituted the major portion of depolarization-activated outward current (Barish and Baud, 1984). Recently, data were reported on the role of NHE1 in neurite morphogenesis, directional migration in primary cilia, and in differentiation of cardiomyocytes (Li et al, 2009;Schneider et al, 2009;Sin et al, 2009). Our experiments revealed that H þ content is regulated gradually, as B<S¼T in 6 and 24 hpa tails, and B¼S<T in 48 hpa tails.…”