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What is Atherosclerosis initiation by fibroblast plaque is mediated by injury to - and explain in detail?
The most acceptable hypothesis for the pathogenesis of atherosclerosis is "the response to injury hypothesis".
According to this hypothesis, atherosclerosis is a chronic inflammatory response of the arterial wall initiated by injury to endothelium.

Pathogenesis of atherosclerosis 
Following stages occurs in the pathogenesis of Atherosclerosis

1. Endothelial injury

Earliest stages of the development of atherosclerosis are mediated by the inflammatory cascade.
Inflammation mediated injury to endothelium is the cornerstone in the development of atherosclerosis.
After the injury, the endothelium is activated and there is increased expression of adhesion molecule-VCAM-1 and there is increased permeability to endothelium.
TNF is the major cytokine to induce this expression.

2. Migration of leukocytes

When VCAM-1 is expressed on endothelium, leukocytes adhere to the endothelium.
Leukocytes then cross the endothelial barrier and begin to accumulate in subendothelial intimal space.
Macrophages engulf LDL cholesterol and form foam cells -> formation of the earliest lesion, i.e. fatty streak.
Macrophages also form oxygen free radicals that cause oxidation of LDL to yield oxidized LDL (modified LDL).

3. Smooth muscle cell migration and proliferation

Inflammatory cells in subendothelial intimal space secrete cytokines, mainly PDGF, TGF-α and FGF which cause migration of smooth muscle cells from media to subendothelial intimal space as well as their proliferation.

4. Maturation of plague

Smooth muscle cells synthesize extracellular matrix (especially collagen) and convert a fatty streak into a mature fibro-fatty atheroma, and contribute to the progressive growth of atherosclerotic lesions.