Stretch-induced alveolar type II cell apoptosis: role of endogenous bradykinin and PI3K-Akt signaling.
Apoptosis of alveolar type II (ATII) cells in response to high-amplitude mechanical stretch represents an important mechanism of ventilation-induced lung injury. Previously, it was demonstrated in an in vitro model that stretch-induced ATII cell apoptosis was prevented by angiotensin-converting enzyme (ACE) inhibitors. This study investigates the mechanism by which ACE inhibitors prevent stretch-induced apoptosis and elucidates the role of bradykinin as an endogenous anti-apoptotic factor. Rat ATII cells cultured on flexible membranes were subjected to cyclic stretch (40 cycles/min; 30% increase in surface area) and compared with static controls. Angiotensinogen, the bradykinin precursor T-kininogen, and bradykinin receptor expression were measured by RT-PCR; Angiotensin II and phosphoinositol 3 OH-kinase (PI3K) activity (as phospho-Akt) were measured by enzyme-linked immunosorbent assay; and Bcl-2 and Bcl-X(L) were measured by Western blot. Stretch did not influence angiotensinogen expression or induce angiotensin II generation. The angiotensin II receptor antagonist saralasin did not prevent stretch-induced apoptosis, whereas ACE inhibitors did. Stretch reduced ATII cell bradykinin release (T-kininogen expression and bradykinin supernatant concentration), and subsequently led to reduced PI3K activity and decreased concentrations of the anti-apoptotic proteins Bcl-2/Bcl-X(L). Bradykinin substitution or addition of keratinocyte or hepatocyte growth factor prevented stretch-induced decrease in PI3K activity and Bcl-2/Bcl-X(L) and reduced stretch-induced apoptosis. Mechanical stretch impairs a constitutively expressed, autocrine anti-apoptotic ATII cell survival signal involving bradykinin-mediated stimulation of the PI3K-Akt-Bcl-2/Bcl-X(L) pathway. Restoration of this pathway prevents stretch-induced apoptosis. This may be beneficial when mechanical ventilation cannot completely avoid alveolar overdistension to maintain oxygenation.
Hammerschmidt
Stefan
S
Department of Respiratory Medicine, University of Leipzig, Leipzig, Germany. stefan.hammerschmidt@t-online.de
Kuhn
Hartmut
H
Gessner
Christian
C
Seyfarth
Hans-Jurgen
HJ
Wirtz
Hubert
H
D000804:Angiotensin II / Q000096:biosynthesis; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001696:Biomechanical Phenomena; D001920:Bradykinin / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D017228:Hepatocyte Growth Factor / Q000494:pharmacology; D007610:Kallikreins / Q000378:metabolism; D008297:Male; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D047228:Angiotensin II Type 1 Receptor Blockers; D000804:Angiotensin II; D017228:Hepatocyte Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D007703:Peptidyl-Dipeptidase A; D007610:Kallikreins; D001920:Bradykinin