吞噬体的酸化对于巨噬细胞的杀菌活性至关重要。调节吞噬体内pH的靶向机制是各种病原体采用的突出策略,这些病原体已成为对公共卫生的主要威胁。新生吞噬体通过涉及与内溶酶体融合的分级成熟过程获得pH调节机制。质子泵和泄漏机制之间的精确协调对于维持吞噬体内的最佳pH至关重要。然而,相对于酸化吞噬体内腔的机制,对这种细胞器中的质子泄漏途径知之甚少。钠质子转运蛋白NHE9是位于核内体上的已知质子泄漏途径。当吞噬体通过与内体融合在成熟过程中获得蛋白质时,NHE9似乎是调节吞噬体上质子通量的有希望的候选者。这里,使用遗传和生物物理方法,我们表明NHE9是与成熟吞噬体相关的重要质子泄漏途径。NHE9在免疫细胞中高表达,特别是巨噬细胞;然而,NHE9表达在细菌感染时强烈下调。我们表明,代偿性异位NHE9表达会阻碍吞噬体沿微管的定向运动,并促进从微管轨道的早期脱离。因此,这些吞噬体的运行长度较短,无法成功到达溶酶体。根据这一观察,我们证明NHE9表达水平与细菌存活呈负相关.一起,我们的研究结果表明,NHE9调节腔pH值影响吞噬体成熟,因此,在巨噬细胞中的杀微生物活性。
Acidification of phagosomes is essential for the bactericidal activity of macrophages. Targeting machinery that regulates pH within the phagosomes is a prominent strategy employed by various pathogens that have emerged as major threats to public health. Nascent phagosomes acquire the machinery for pH regulation through a graded maturation process involving fusion with endolysosomes. Meticulous coordination between proton pumping and leakage mechanisms is crucial for maintaining optimal pH within the phagosome. However, relative to mechanisms involved in acidifying the phagosome lumen, little is known about proton leakage pathways in this organelle. Sodium proton transporter
NHE9 is a known proton leakage pathway located on the endosomes. As phagosomes acquire proteins through fusions with endosomes during maturation,
NHE9 seemed a promising candidate for regulating proton fluxes on the phagosome. Here, using genetic and biophysical approaches, we show NHE9 is an important proton leakage pathway associated with the maturing phagosome.
NHE9 is highly expressed in immune cells, specifically macrophages; however,
NHE9 expression is strongly downregulated upon bacterial infection. We show that compensatory ectopic NHE9 expression hinders the directed motion of phagosomes along microtubules and promotes early detachment from the microtubule tracks. As a result, these phagosomes have shorter run lengths and are not successful in reaching the lysosome. In accordance with this observation, we demonstrate that
NHE9 expression levels negatively correlate with bacterial survival. Together, our findings show that
NHE9 regulates lumenal pH to affect phagosome maturation, and consequently, microbicidal activity in macrophages.