Mechanotransduction of stem cells for tendon repair

Table 1 Difference among tendon stem/progenitor cells, bone marrow-derived mesenchymal stem cells, and adipose-derived stem cells for tendon repair

	TSPCs	BM-MSCs	ASCs
Morphology	Fibroblast-like shape[22]	Spindle-shaped[35]	Spindle-shaped[45]
Phenotypes	Positive: CD13, C29, CD44, CD54, CD73, CD90, CD105, CD146 and CD166 Negative: CD2, CD3, CD11b, CD14, CD15, CD16, CD18, CD19, CD31, CD34, CD45, CD56, CD71, CD106, CD117, CD123, and CD235a[4,22,23]	Positive: CD13, CD29, CD44, CD73, CD90, and CD105 Negative: CD14, CD19, CD34, CD45[35,37]	Positive: CD13, C29, CD44, CD49d, CD54, CD73, CD90, CD105, and CD166 Negative: CD14, CD19, CD31, CD34, CD45 and CD71[23,35,46]
Proliferation	TSPCs = BM-MSCs[4]; TSPCs ≤ ASCs[23]	BM-MSCs = TSPCs[4]; BM-MSCs < ASCs[38]	ASCs > BM-MSCs[38]; ASCs ≥ TSPCs[23]
Tenogenic differentiation	Spontaneous differentiation[20], or promoted by growth factors[120] and mechanical loading[75]	Induced by growth factors[36] and mechanical loading[39]	Induced by growth factor supplements[48,49] and extracorporeal shockwave[50]
Evidence for tendon repair in vitro	Tenogenic differentiation[20,75,120] and high proliferation potential[4,28]	Tenogenic differentiation and high proliferation potential[4]; enhanced secretion of bioactive factors[40] and the deposition of ECM[41]	Tenogenic differentiation and high proliferation rate[51]
Evidence for tendon repair in vivo	High proliferation and activation of tenogenesis[29]; improved collagen alignment and biomechanical properties[30,31]	Improved histological and biomechanical properties; increased expression of collagen[42,43]	Modulation of microenvironment[55]; enhancing the secretion of collagen and mechanical strength of tendon[52,53]
Evidence for tendon repair in clinics	None	Four registered trials, but the results are not available	Reduction of pain, tendon defect areas post intervention[56]
Advantages	Spontaneous tenogenic differentiation[20]; higher proliferation and therapeutic effectiveness[31]	Easier acquirement[33]; enhanced secretion of bioactive factors[40]; increased the deposition of collagenous proteins[41]	Easier acquirement[34]; inhibition of osteogenic differentiation[55]; confirmed clinical outcome[56]
Limitations	Limited number obtained from isolation[63]	High potential of osteogenic differentiation[44]; lower therapeutic effectiveness than TSPCs[31]	Risk of fibrotic tissue formation, scarring[57], and forming adipocytes[58]

TSPCs: Tendon stem/progenitor cells; BMSCs: Bone marrow-derived mesenchymal stem cells; ASCs: Adipose-derived stem cells; ECM: Extracellular matrix.