During angiogenesis recruitment of pericytes and peri-endothelial cells is due to –
**Core Concept**
Angiogenesis is the complex process of new blood vessel formation from pre-existing vessels, involving various cell types, growth factors, and signaling pathways. The recruitment of pericytes and peri-endothelial cells is a critical step in stabilizing the newly formed blood vessels.
**Why the Correct Answer is Right**
Angiopoietins, specifically Ang-1 and Ang-2, play a crucial role in the recruitment of pericytes and peri-endothelial cells during angiogenesis. Ang-1 binds to its receptor Tie-2 on the surface of endothelial cells, promoting the association of pericytes and peri-endothelial cells with the endothelial cells, thereby stabilizing the vessels. TGF-β (transforming growth factor-beta) also contributes to this process by promoting the differentiation of pericytes and regulating the expression of adhesion molecules. PDGF (platelet-derived growth factor) further supports the recruitment of pericytes by promoting their proliferation and migration.
**Why Each Wrong Option is Incorrect**
**Option A:** VEGF (vascular endothelial growth factor) is essential for angiogenesis, but it primarily promotes endothelial cell proliferation and migration, rather than pericyte recruitment. PDGF is also involved, but VEGF is not the primary factor in this context.
**Option B:** TGF-β is indeed involved in angiogenesis, but the combination of TGF-β, VEGF, and PDGF does not accurately represent the key factors involved in pericyte recruitment. Ang-1 and Ang-2 are more specific to this process.
**Option C:** IL-2 and IL-6 are cytokines involved in various immune responses, but they are not directly related to pericyte recruitment during angiogenesis.
**Clinical Pearl / High-Yield Fact**
The interaction between Ang-1 and Tie-2 is a critical regulator of vascular stability, and dysregulation of this pathway has been implicated in various vascular diseases, including cancer and atherosclerosis.
**Correct Answer Line**
✓ Correct Answer: D. Angiopoietins, TGF & PDGF