Signaling pathways regulating a phenotypic modulation of smooth muscle cells

在之前的研究中，我们发现IGF-I在培养的砂眼SMCs中触发磷酸肌肽3-激酶（PI3-K）和蛋白激酶B(PKB(Akt))，该信号通路在维持SMCs分化表型中起着至关重要的作用。在这里，我们使用上述的原代培养系统研究了PDGF-BB、bFGF和EGF诱导砂囊SMCs去分化的信号通路。与igf - i触发的通路相反，PDGF-BB、bFGF和EGF协同激活ERK和p38MAPK通路。此外，即使在IGF-I刺激SMCs时，MEK1和MKK6的活性形式（分别是ERK和p38MAPK的上游激酶）的强制表达也会诱导去分化。在三种生长因子中，PDGF-BB除了ERK和p38MAPK通路外，仅触发PI3-K/PKB （Akt）通路。当ERK和p38MAPK通路同时被其特异性抑制剂阻断或PI3-K或PKB （Akt）的活性形式被阻断时，PDGF-BB反过来启动维持分化的SMC表型。我们将这些发现应用于血管SMC，并证明了相同的信号通路可能参与调节血管SMC表型的可能性。这些结果表明，PI3-K/PKB （Akt）通路与ERK和p38MAPK通路之间平衡的变化将决定内脏和血管SMCs的表型。此外，我们使用mRNA减法揭示SMCs表型调节的分子机制。通过这种方法，我们发现编码同型细胞粘附分子cadherin 6B的10 kb mRNA在分化的血管和内脏SMCs中强烈表达，但在它们衍生的去分化SMCs中不表达。在体内，除了脑、脊髓、视网膜和肾脏外，钙粘蛋白6B在鸡胚胎发育后期的血管和内脏SMCs中也有表达。这些结果表明，钙粘蛋白6B是一种新的SMC表型标记分子，参与了SMCs的晚期分化。少

In previous study, we found that IGF-I triggered the phosphoinositide 3-kinase (PI3-K) and protein kinase B (PKB(Akt)) in cultured gizzard SMCs and this signaling pathway played a vital role in maintaining a differentiated phenotype of SMCs. Here, we investigated the signaling pathways involved in dedifferentiation of gizzard SMCs induced by PDGF-BB, bFGF, and EGF using the primary culture system described above. In contrast to the IGF-I-triggered pathway, PDGF-BB, bFGF, and EGF coordinately activated ERK and p38MAPK pathways. Further, the forced expression of active forms of MEK1 and MKK6, which are the upstream kinases of ERK and p38MAPK, respectively, induced dedifferentiation even when SMCs were stimulated with IGF-I. Among three growth factors, PDGF-BB only triggered the PI3-K/PKB (Akt) pathway in addition to the ERK and p38MAPK pathways. When the ERK and p38MAPK pathways were simultaneously blocked by their specific inhibitors or an active form of either PI3-K or PKB (Akt) was tr … More ansfected, PDGF-BB in turn initiated to maintain the differentiated SMC phenotype. We applied these findings to vascular SMCs, and demonstrated the possibility that the same signaling pathways might be involved in regulating the vascular SMC phenotype. These results suggest that changes in the balance between the PI3-K/PKB (Akt) pathway and the ERK and p38MAPK pathways would determine phenotypes of visceral and vascular SMCs.Further, we used mRNA subtraction method to reveal the molecular mechanisms underlying the phenotypic modulation of SMCs. With this approach, we found that a 10 kb mRNA encoding a homotypic cell adhesion molecule, cadherin 6B, was strongly expressed in differentiated vascular and visceral SMCs, but not in the dedifferentiated SMCs derived from them. In vivo, cadherin 6B was expressed in vascular and visceral SMCs, in addition to brain, spinal cord, retina, and kidney, at a late stage of chicken embryonic development. These results suggest that cadherin 6B is a novel molecular marker for SMC phenotype and is involved in the late differentiation of SMCs. Less