The most important cytokine for the synthesis and deposition of connective tissue proteins is?
The laying down of connective tissue occurs in two steps: 

Migration and proliferation of fibroblasts into the site of injury.
Deposition of ECM proteins produced by these cells. 

These processes are orchestrated by locally produced cytokines and growth factors, including PDGF, FGF-2, and TGF-β.
TGF-β is the most important cytokine for the synthesis and deposition of connective tissue proteins.
Robin’s Textbook of pathology 10th ed Page 91
PDGF
FGF-2
TGF-β
MMP