Preferential accumulation and export of high molecular weight FGF-2 by rat cardiac non-myocytes.
OBJECTIVE
fibroblast growth factor-2 (FGF-2), implicated in paracrine induction of cardiac hypertrophy, is translated as high molecular weight (Hi-FGF-2) and low molecular weight (Lo-FGF-2) isoforms. Paracrine activities are assigned to Lo-FGF-2, whereas Hi-FGF-2 is presumed to have nuclear functions. In this work, we re-examined the latter presumption by asking whether: cardiac non-myocytes (CNMs) accumulate and export Hi-FGF-2 in response to pro-hypertrophic [angiotensin II (Ang II)] stimuli; an unconventional secretory pathway requiring activated caspase-1 affects Hi-FGF2 export; and secreted Hi-FGF-2 is pro-hypertrophic.


RESULTS
using neonatal rat heart-derived cultures and immunoblotting, we show that CNMs accumulated over 90% Hi-FGF-2, at levels at least five-fold higher than cardiomyocytes (CMs). Pro-hypertrophic agents (Ang II, endothelin-1, and isoproterenol) up-regulated CNM-associated Hi-FGF-2. The Ang II effect was mediated by Ang II receptor-1 but not Ang II receptor-2 as it was blocked by losartan but not PD123319. CNM-derived Hi-FGF-2 was detected in two extracellular pools: in conditioned medium from Ang II-stimulated CNMs and in association with the cell surface/matrix, eluted with a gentle 2 M NaCl wash of the cell monolayer. Conditioned medium from Ang II-treated CNMs increased neonatal CM size, an effect prevented by anti-FGF-2-neutralizing antibodies. The caspase-1 inhibitor YVAD prevented the Ang II-induced release of Hi-FGF-2 to both extracellular pools.


CONCLUSIONS
CNMs are major producers of Hi-FGF-2, up-regulated by hypertrophic stimuli and exported to the extracellular environment by a mechanism requiring caspase-1 activity, suggesting a link to the innate immune response. Hi-FGF-2 is likely to promote paracrine induction of myocyte hypertrophy in vivo.
Santiago
Jon-Jon
JJ
Institute of Cardiovascular Sciences, St Boniface Research Centre, 351 Taché Avenue, Winnipeg, Manitoba, Canada R2H 2A6.
Ma
Xin
X
McNaughton
Leslie J
LJ
Nickel
Barbara E
BE
Bestvater
Brian P
BP
Yu
Liping
L
Fandrich
Robert R
RR
Netticadan
Thomas
T
Kardami
Elissavet
E
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D006332:Cardiomegaly / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D020170:Caspase 1 / Q000378:metabolism; D049108:Cell Enlargement / Q000187:drug effects; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D016222:Fibroblast Growth Factor 2 / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007113:Immunity, Innate; D008970:Molecular Weight; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D058628:Myofibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D044139:Receptor, Angiotensin, Type 2 / Q000378:metabolism
D017077:Culture Media, Conditioned; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D016222:Fibroblast Growth Factor 2; D000804:Angiotensin II; D020170:Caspase 1