Mechanosensitive channels TMEM63A and TMEM63B mediate lung inflation–induced surfactant secretion
Gui-Lan Chen, … , Jin Zhang, Bo Zeng
Gui-Lan Chen, … , Jin Zhang, Bo Zeng
Published December 21, 2023
Citation Information: J Clin Invest. 2024;134(5):e174508. https://doi.org/10.1172/JCI174508.
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Mechanosensitive channels TMEM63A and TMEM63B mediate lung inflation–induced surfactant secretion

Abstract

Pulmonary surfactant is a lipoprotein complex lining the alveolar surface to decrease the surface tension and facilitate inspiration. Surfactant deficiency is often seen in premature infants and in children and adults with respiratory distress syndrome. Mechanical stretch of alveolar type 2 epithelial (AT2) cells during lung expansion is the primary physiological factor that stimulates surfactant secretion; however, it is unclear whether there is a mechanosensor dedicated to this process. Here, we show that loss of the mechanosensitive channels TMEM63A and TMEM63B (TMEM63A/B) resulted in atelectasis and respiratory failure in mice due to a deficit of surfactant secretion. TMEM63A/B were predominantly localized at the limiting membrane of the lamellar body (LB), a lysosome-related organelle that stores pulmonary surfactant and ATP in AT2 cells. Activation of TMEM63A/B channels during cell stretch facilitated the release of surfactant and ATP from LBs fused with the plasma membrane. The released ATP evoked Ca2+ signaling in AT2 cells and potentiated exocytic fusion of more LBs. Our study uncovered a vital physiological function of TMEM63 mechanosensitive channels in preparing the lungs for the first breath at birth and maintaining respiration throughout life.

Authors

Gui-Lan Chen, Jing-Yi Li, Xin Chen, Jia-Wei Liu, Qian Zhang, Jie-Yu Liu, Jing Wen, Na Wang, Ming Lei, Jun-Peng Wei, Li Yi, Jia-Jia Li, Yu-Peng Ling, He-Qiang Yi, Zhenying Hu, Jingjing Duan, Jin Zhang, Bo Zeng

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Figure 5

Deficiency of TMEM63A/B abolishes ventilation-induced Ca2+ transients and surfactant release in AT2 cells.

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Deficiency of TMEM63A/B abolishes ventilation-induced Ca2+ transients an...
(A) mCherry fluorescence in AAV-infected (CAG-DIO-jGCaMP7s-mCherry–infected) lungs showing positively transduced AT2 cells (brighter spots). Sftpc-63ab represents Sftpc-CreERT2+/– 63afl/fl 63bfl/fl. Scale bar: 100 μm. (B) The densities of positively transduced AT2 cells were comparable between the control Sftpc-CreERT2 and Sftpc-63ab mice. n = 5 lung lobes. NS, nonsignificant, by 2-tailed, unpaired Student’s t test. (C) Lung inflation–induced Ca2+ transients in AT2 cells were completely abolished in all lung lobes from Sftpc-63ab mice, as revealed by jGCaMP7s fluorescence. n = 5 lung lobes. ***P < 0.001, by 1-way ANOVA with Tukey’s test. (D) Survival curves for Tmem63a/b-cDKO mice that received daily inhalation (30 min each time, 3 times/day) of aerosolized ATP (200 mM) or saline solution after tamoxifen induction. n = 3 mice. (E) ATP-induced Ca2+ response in primary AT2 cells isolated from Ctrl-63ab (63afl/fl 63bfl/fl) and Sftpc-63ab mice (n = 30 and 35 cells, respectively). (F) Cell strain–induced surfactant release occurred in AT2 cells from Ctrl-63ab, but not Sftpc-63ab, mice. Unfused LBs were stained by LysoTracker Green; LBs fused on the plasma membrane were positive for FM4-64. Arrows indicate LBs that released surfactant (FM4-64 fluorescence disappeared after strain). Scale bar: 5 μm. (G and H) Tmem63a/b-cDKO did not affect ATP-induced LB fusion but significantly attenuated cell strain–induced surfactant release. Ctrl, Ctrl-63ab; KO, Sftpc-63ab. The median and quartiles are shown by dashed and dotted lines, respectively. The numbers of cells are shown at the bottom. *P < 0.05 and ***P < 0.001, by 1-way ANOVA with Tukey’s test. (I) Reacidification of LBs after removal of ATP in AT2 cells from Sftpc-63ab mice. Overlapped LysoTracker Green and FM4-64 fluorescence (orange, indicated by the arrow) suggests that the fusion pore was closed and luminal pH was reacidified. Scale bar: 5 μm. (J and K) Transmission electron microscopy images and cross-sectional areas (CSAs) of LBs from Ctrl-63ab and Sftpc-63ab mice. n = 41 and 94 LBs, respectively. Scale bars: 1 μm.