Acidic pH is essential for maintaining mast cell secretory granule homeostasis

Abstract

It has been recognized for a long time that the secretory granules of mast cells are acidic, but the functional importance of maintaining an acidic pH in the mast cell granules is not fully understood. Here we addressed this issue by examining the effects of raising the pH of the mast cell secretory granules. Mast cells were incubated with bafilomycin A1, an inhibitor of the vacuolar-type ATPase proton pump. Supporting a role of vacuolar-type ATPase in mast cell granule acidification, bafilomycin A1 treatment caused a robust increase in granule pH. This was accompanied by marked effects on mast cell granules, including swelling and acquisition of vacuole-like morphology. Moreover, bafilomycin A1 caused extensive, yet selective effects on the granule content. These included aberrant processing of pro-carboxypeptidase A3 and a reduction in the level of intracellular histamine, the latter being accompanied by an increase in extracellular histamine. In contrast, the storage of β-hexosaminidase, a prototype lysosomal hydrolase known to be stored in mast cell granules, was not affected by abrogation of granule acidification. Moreover, bafilomycin A1 caused a reduction of tryptase enzymatic activity and appearance of tryptase degradation products. Tryptase inhibition prevented the formation of such degradation products, suggesting that the pH elevation causes tryptase to undergo autoproteolysis. Taken together, our findings reveal that mast cell secretory granule homeostasis is critically dependent on an acidic milieu.

Inhibition of silkworm vacuolar‐type ATPase activity by its inhibitor Bafilomycin A1 induces caspase‐dependent apoptosis in an embryonic cell line of silkworm

“…In cells, Baf‐A1 usually targets to the lysosomes for regulating cellular acidification (Yamamoto et al, ). The acidification of lysosomes revealed by the incubation with acridine orange was completely inhibited when cells were treated with 0.1–1 μM bafilomycin A1, then intracellular pH robust increased (Marrone et al, ; Pejler, Hu Frisk, Sjostrom, Paivandy, & Ohrvik, ; Yoshimori, Yamamoto, Moriyama, Futai, & Tashiro, ). Generally, cell acidification is essential for cell proliferation, autophagy, and apoptosis.…”

Immune Modulation as a Therapeutic Option During the SARS-CoV-2 Outbreak: The Case for Antimalarial Aminoquinolines

“…These observations were confirmed ex vivo in human primary MCs ( 38 ). MC cytoplasm is notoriously packed with secretory granules, which display an acidic pH of 5.2 to 6.1, optimal for MC proteases ( 77 ). Experiments performed with bafilomycin A1, an inhibitor of vacuolar-type H + -ATPase (V-ATPase) sharing with CQ/HCQ the lysosomal tropism and the ability to increase pH in acidic compartments, showed that disruption of the acidic pH of MC secretory granules induced tryptase degradation ( 77 ).…”

“…MC cytoplasm is notoriously packed with secretory granules, which display an acidic pH of 5.2 to 6.1, optimal for MC proteases ( 77 ). Experiments performed with bafilomycin A1, an inhibitor of vacuolar-type H + -ATPase (V-ATPase) sharing with CQ/HCQ the lysosomal tropism and the ability to increase pH in acidic compartments, showed that disruption of the acidic pH of MC secretory granules induced tryptase degradation ( 77 ). CQ/HCQ would be expected to reproduce such findings, whose main interest resides in the abrogation of the proinflammatory signals and effectors that are conveyed by intact MC proteases, such as tryptase, the best known in humans, which is involved in chronic allergic inflammation and tissue remodeling ( 77 – 79 ).…”

Der kausale Zusammenhang von Prostata-Hyperplasie, chronischer Prostatitis und Prostatakrebs

“…Auch bei der Degranulation von Mastzellen spielt der pH-Wert eine entscheidende Rolle. Nur im sauren Milieu entwickelt der inflammatorische Cocktail seine volle Kraft [31].…”