Figure 5.

Schematic diagram displays the possible theories of IDO1 mechanisms by which IDO effects Sox9 signaling in the MSCs leading to inhibit chondrogenic genes. As known IDO1 induces Wnt signaling that directly inhibits Sox9 and consequently Col2a, Col9a, and aggrecan. Also, IDO has the capability to inhibit PKA, CCR2, or Hif-α which work as Sox9 upstream molecules. Indeed, IDO1 could directly elicits ERK1/2 signaling that directly inhibits Sox9 and subsequently inhibits chondrogenic genes.