Fujisaki Hitomi, Ebihara Tetsuya, Irie Shinkichi, Kobayashi Takashi, Adachi Eijiro, Mochitate Katumi, Hattori Shunji
Nippi Research Institute of Biomatrix, Toride-shi, Ibaraki, Japan.
Connect Tissue Res. 2007;48(3):159-69. doi: 10.1080/03008200701364392.
Keratinocytes adhere and proliferate well on collagen-coated surfaces, but they undergo apoptosis without differentiation on collagen gels according to our past research. In the current studies, we investigated the necessary conditions for keratinocyte survival on fibrous collagen gels. We found that keratinocytes survived on collagen gels when the medium contains elevated levels (1.8 mM) of calcium. Under this high calcium condition, cells formed multicellular colonies and differentiated. Akt was not activated in cells cultured on collagen gels regardless of the calcium concentration, whereas it was activated in cells cultured on nonfibrous collagen. On the other hand, Erk1/2, key kinases of MAPK pathway, were phosphorylated in cells cultured under high calcium condition but not in cells cultured on collagen gels under low calcium condition. The necessity of Erk1/2 activation for keratinocyte survival on collagen gel was confirmed with experiment using U0126, an inhibitor for Erk1/2. These studies show that activation of Akt depends on collagen assembly, whereas activation of Erk1/2 is induced by increased extracellular calcium concentration. Thus, activation of the Erk1/2 by increasing calcium concentration in the incubation medium may compensate for the loss of Akt activation, allowing keratinocyte survival on collagen gels.
根据我们过去的研究，角质形成细胞在胶原包被的表面上能很好地黏附并增殖，但在胶原凝胶上它们会发生凋亡而不分化。在当前的研究中，我们调查了角质形成细胞在纤维状胶原凝胶上存活的必要条件。我们发现，当培养基中钙水平升高（1.8 mM）时，角质形成细胞能在胶原凝胶上存活。在这种高钙条件下，细胞形成多细胞集落并分化。无论钙浓度如何，在胶原凝胶上培养的细胞中Akt都未被激活，而在非纤维状胶原上培养的细胞中Akt被激活。另一方面，MAPK途径的关键激酶Erk1/2在高钙条件下培养的细胞中被磷酸化，但在低钙条件下胶原凝胶上培养的细胞中未被磷酸化。使用Erk1/2抑制剂U0126进行的实验证实了Erk1/2激活对角质形成细胞在胶原凝胶上存活的必要性。这些研究表明，Akt的激活取决于胶原组装，而Erk1/2的激活是由细胞外钙浓度增加诱导的。因此，通过增加孵育培养基中的钙浓度来激活Erk1/2可能补偿Akt激活的缺失，从而使角质形成细胞在胶原凝胶上存活。
