*3.4.4. Receptor tyrosine kinase*

Receptor tyrosine kinase (c-kit) is expressed by bone marrow and involved in intracellular signaling. It plays an important role in cell proliferation, cell adhesion, cell survival, and neovascularization [89]. Several studies have shown that C-kit plays an important role in the angiogenic process of PDR. C-kit has a soluble form called s-kit that can be generated by proteolytic cleavage [90]. Abu et al. found an increase of c-kit expression in membranes from patients with active neovascularization (697.4 ± 1528.1 pg/mL) compared to patients with inactive PDR (205.3 ± 106.4 pg/mL) and control patients (87.5 ± 91.5 pg/mL). This demonstrates that an increase of c-kit expression is correlated to the progression of PDR [90]. However, Lee et al. found a slight decrease of c-kit values in the PDR group compared to NPDR group [91].
