Immunohistochemical Characterization of Cells in Adult Human Patellar Tendons

Abstract

S U M M A R Y Cells in tendons are conventionally identified as elongated tenocytes and ovoid tenoblasts, but specific markers for these cells are not available. The roles and interplay of these cells in tendon growth, remodeling, and healing are not well established. Therefore, we proposed to characterize these cells with respect to cell turnover, extracellular matrix metabolism, and expression of growth factors. Here we examined 14 healthy human patellar tendon samples for the expression of various proteins in tenocytes and tenoblasts, which were identified as elongated tendon cells and ovoid tendon cells, respectively. Matrix metalloproteinase 1 (MMP1), procollagen type I (procol I), heat shock protein 47 (hsp47), bone morphogenetic protein 12 (BMP12), 13 (BMP13), and transforming growth factor ␤ 1 (TGF ␤ 1) were detected by immunohistochemistry (IHC). An image analysis of the IHC staining for proliferation cell nuclear antigen (PCNA) and apoptotic cells was performed to determine the proliferation index and the apoptosis index in elongated and ovoid tendon cells. The ovoid tendon cells expressed higher levels of procol I, hsp47, MMP1, BMP12, BMP13, and TGF ␤ 1 than the elongated tendon cells. Both the proliferation index and the apoptosis index of ovoid tendon cells were higher than those of the elongated tendon cells. The results suggested that ovoid tendon cells, conventionally recognized as tenoblasts, were more active in matrix remodeling. The expression of BMP 12, BMP13 and TGF ␤ 1 might be associated with the different cellular activities of tenoblasts and tenocytes.

The past, present and future in scaffold-based tendon treatments

“…They form a network of cellular protrusions, allowing them to react cohesively to external forces and enabling the tissue to react best to mechanical demands [61]. Tenoblasts vary in size and shape ranging from round, spherical or cuboid to spindle star like morphologies of between 20 and 70µm in length and 8 to 20µm in width and have been considered to be the major cell type responsible for tissue remodelling [62]. Upon maturation into TCs, they become elongated with up to 300µm length and less metabolically active [63], suggesting that they play different role in tendon physiology than tenoblasts.…”

In vitro and in vivo effects of PDGF-BB delivery strategies on tendon healing: a review

“…Tenocytes, spindle-shaped and elongated, are the most numerous cell population and they are responsible for the formation/turnover of extracellular matrix, assembly of early collagen fibres and facilitation of collagen network adaptation to external stimuli (Milz et al, 2009). Tenoblasts, on the other hand, can vary in size and shape and are considered to be responsible for matrix (tissue) remodelling (Chuen et al, 2004). Tendon stem/ progenitor cells have been recently discovered and their capacity to differentiate into bone, cartilage or fat has been observed (Bi et al, 2007), as well as, the expression of certain stem cells markers (Oct4 and SSEA4 among others) (Lui and Chan, 2011;Zhang and Wang, 2010b).…”

The Basic Science of Tendinopathy

“…Fibroblast-like cells are the major cell type in tendons, and have been histologically classified as elongated tenocytes or ovoid tenoblasts [25,53]. These cells are important for maintenance of healthy tendon as they can proliferate, produce collagen and maintain the appropriate extracellular matrix [19,53].…”

“…These cells are important for maintenance of healthy tendon as they can proliferate, produce collagen and maintain the appropriate extracellular matrix [19,53]. Ovoid tenoblasts -often described as an immature or activated form of tenocytes -have a higher proliferation index and apoptosis index than those of elongated tenocytes [25]. There is evidence that changes occur in the cells (tenocytes appear rounder, proliferate, become necrotic or apoptotic, and have an increased expression of local insulin-like growth factor-1 (IGF-1)) before the overt development of tendinopathy [8,28,96].…”