The mechanisms underlying fibroblast apoptosis regulated by growth factors during wound healing.
While investigating the mechanisms underlying cell death during wound healing processes, we uncovered the pro-apoptotic effects of basic fibroblast growth factor (bFGF) on granulation tissue fibroblasts following pretreatment with transforming growth factor (TGF)-beta1 in vitro. bFGF induced caspase-3 activation and apoptosis in TGF-beta1-pretreated granulation tissue-derived fibroblasts (GF-1) following bFGF treatment for 48 and 96 h. In contrast, fibroblasts that had been treated in the same manner and that originated from the uninjured dermis did not display apoptosis, indicating that the mechanisms underlying apoptosis events in fibroblasts that originate from normal dermal and wound tissues differ. In this process, we also found that bFGF inhibited Akt phosphorylation at serine 473 and induced a rapid loss of phosphorylation of focal adhesion kinase (FAK) at tyrosine 397 in pretreated GF-1 cells, an event that coincided with the dissociation of phosphorylated FAK from the focal adhesions. Therefore, inhibition of survival signals relayed via the disrupted focal adhesion structures and inactivated Akt following bFGF treatment may lead to apoptosis in GF-1 cells pretreated with TGF-beta1. Pretreatment of GF-1 with TGF-beta1 followed by the addition of bFGF resulted in significantly greater inhibition of phosphorylation of Akt and FAK compared to treatment with TGF-beta1 or bFGF alone. The combinatorial treatment also led to proteolysis of FAK and inhibition of FAK and Akt protein expression in GF-1 cells. These findings demonstrated a significant role for the two cytokines in apoptosis of granulation tissue fibroblasts during wound healing. In vivo studies also confirmed a marked decline in phosphorylation and protein expression of Akt and FAK in bFGF-injected skin wounds. These results led to the hypothesis that temporal activation of TGF-beta1 and bFGF at the injury site promotes apoptosis in granulation tissue fibroblasts, an event that is critical for the termination of proliferative granulation tissue formation.
Department of Pathology, School of Medicine, Toho University, 5-21-16 Omori-Nishi, Ohta-City, Tokyo, 143-8540, Japan. akasakay@med.toho-u.ac.jp
Yoshikiyo
Y
Akasaka
Ichiro
I
Ono
Takafumi
T
Kamiya
Yukio
Y
Ishikawa
Toshio
T
Kinoshita
Shigeki
S
Ishiguro
Tomoko
T
Yokoo
Risa
R
Imaizumi
Naomi
N
Inomata
Kazuko
K
Fujita
Yuri
Y
Akishima-Fukasawa
Miwa
M
Uzuki
Kinji
K
Ito
Toshiharu
T
Ishii
D000199:Actins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D051417:Focal Adhesion Kinase 1 / Q000378:metabolism; D006097:Granulation Tissue / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D051496:Receptor, Fibroblast Growth Factor, Type 1 / Q000378:metabolism; D012867:Skin / Q000293:injuries / Q000378:metabolism / Q000473:pathology; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology; D014945:Wound Healing / Q000187:drug effects* / Q000502:physiology
D000199:Actins; D053148:Caspase 3; D016222:Fibroblast Growth Factor 2; D051417:Focal Adhesion Kinase 1; D051057:Proto-Oncogene Proteins c-akt; D051496:Receptor, Fibroblast Growth Factor, Type 1; D053773:Transforming Growth Factor beta1; C498862:Acta2 protein, rat; C496350:Fgfr1 protein, rat; C496052:Ptk2 protein, rat