Intestinal NaCl, HCO₃^- and fluid absorption are strongly dependent on apical Na⁺/H⁺ exchange. The intestine expresses three presumably apical NHE isoforms, NHE2, NHE3 and NHE8. We addressed the role of NHE8 (SLC9A8) and its interplay with NHE2 (SLC9A2) in luminal proton extrusion during acute and chronic enterocyte acidosis, and studied the differential effects of NHE8 and NHE2 on enterocyte proliferation. In contrast to NHE3, which was upregulated in differentiated vs. undifferentiated colonoids, the expression of NHE2 and NHE8 remained constant during differentiation of colonoids and Caco2Bbe cells. Heterogeneously expressed Flag-tagged rat (r)Nhe8 and human (h)NHE8 translocated to the apical membrane of Caco2Bbe cells. rNhe8 and hNHE8, when expressed in NHE-deficient PS120 fibroblasts showed higher sensitivity to HOE642 compared to NHE2. Lentiviral shRNA knockdown of endogenous NHE2 in Caco2Bbe cells (C2Bbe/shNHE2) resulted in a decreased steady-state pH_i, an increased NHE8 mRNA expression, and augmented NHE8-mediated apical NHE activity. Lentiviral shRNA knockdown of endogenous NHE8 in Caco2Bbe cells (C2Bbe/shNHE8) resulted in a decreased steady-state pH_i as well, accompanied by decreased NHE2 mRNA expression and activity, which together contributed to reduced apical NHE activity in the NHE8-knockdown cells. Chronic acidosis increased NHE8 but not NHE2 mRNA expression. Alterations in NHE2 and NHE8 expression/activity affected proliferation, with C2Bbe/shNHE2 cells having lower and C2Bbe/shNHE8 having higher proliferative capacity, accompanied by amplified ERK1/2 signaling pathway and increased EGFR expression in the latter cell line. Thus, both Na⁺/H⁺ exchangers have distinct functions during cellular homeostasis by triggering different signaling pathways to regulate cellular proliferation and pH_i-control.

中文翻译：

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钠/氢交换器 8 的功能表征及其在结肠上皮细胞增殖中的作用

肠道 NaCl、HCO ₃ ^-和液体吸收强烈依赖于顶端 Na ⁺ /H ⁺交换。肠道表达三种推测的顶端 NHE 同种型，NHE2、NHE3 和 NHE8。我们解决了 NHE8 (SLC9A8) 的作用及其与 NHE2 (SLC9A2) 在急性和慢性肠细胞酸中毒期间管腔质子挤出中的相互作用，并研究了 NHE8 和 NHE2 对肠细胞增殖的不同影响。与 NHE3 相比，NHE3 在分化的和未分化的结肠中上调，NHE2 和 NHE8 的表达在结肠和 Caco2Bbe 细胞分化过程中保持恒定。异质表达的标记有 Flag 标签的大鼠 (r)Nhe8 和人类 (h)NHE8 易位到 Caco2Bbe 细胞的顶端膜。rNhe8 和 hNHE8 在 NHE 缺陷型 PS120 成纤维细胞中表达时，与 NHE2 相比，对 HOE642 的敏感性更高。_i，增加的NHE8 mRNA表达和增强的NHE8介导的顶端NHE活性。Caco2Bbe 细胞 (C2Bbe/shNHE8) 中内源性 NHE8 的慢病毒 shRNA 敲低也导致稳态 pH _i降低，伴随着 NHE2 mRNA 表达和活性降低，这共同导致 NHE8 敲低细胞中顶端 NHE 活性降低。慢性酸中毒增加 NHE8 但不增加 NHE2 mRNA 表达。NHE2 和 NHE8 表达/活性的改变影响增殖，C2Bbe/shNHE2 细胞具有较低的增殖能力，C2Bbe/shNHE8 具有较高的增殖能力，伴随着 ERK1/2 信号通路的放大和后者细胞系中 EGFR 表达的增加。因此，Na ⁺ /H ⁺通过触发不同的信号通路来调节细胞增殖和 pH _i控制，交换器在细胞稳态过程中具有不同的功能。