Regulation of Hypoxia-Induced Cell Death in Human Tenocytes

Abstract

Degenerate shoulder tendons display evidence of hypoxia. However tendons are relatively avascular and not considered to have high oxygen requirements and the vulnerability of tendon cells to hypoxia is unclear. Cultured human tenocytes were exposed to hypoxia and the cellular response detected using QPCR, Western blotting, viability, and ELISA assays. We find that tenocytes respond to hypoxia in vitro by activating classical HIF-1α-driven pathways. Total hypoxia caused significant tenocyte apoptosis. Transcription factors typically involved in hypoxic response, HIF-1α and FOXO3A, were upregulated. Hypoxia caused sustained upregulation of several proapoptotic proteins known to mediate hypoxia-induced apoptosis, such as Bnip3 and Nix, but others were unchanged although they were reportedly hypoxia-sensitive in other cell types. Antiapoptotic proteins Bcl2 and Bcl-xL were unchanged by hypoxia. Normal human tenocytes expressed all isoforms of the hypoxia-induced vascular growth factor VEGF except VEGF-D. Hypoxia markedly upregulated VEGF-A mRNA, followed by increased VEGF protein secretion. However treatment with VEGF did not improve tenocyte survival. As a protective strategy for tenocytes at risk of hypoxic death we added prosurvival growth factors insulin or platelet rich plasma (PRP). Both agents strongly protected tenocytes from hypoxia-induced death over 48 h, suggesting possible efficacy in the acute postrupture tendon or integrating graft.

Significant association of full-thickness rotator cuff tears and estrogen-related receptor-β (ESRRB)

“…8,9 Furthermore, various genetically controlled biological mechanisms have been recognized to contribute to rotator cuff disease and similar tendinopathies, including apoptosis and factors that influence the regulation of the extracellular matrix. [12][13][14][15][16]30 Motta et al 20 recently tested 23 single nucleotide polymorphisms (SNPs) from 6 candidate genes involved in the repair and degenerative processes of musculoskeletal tissue (DEFB1, DENND2C, ESRRB, FGF3, FGF10, and FGFR1) for a potential association with rotator cuff disease. The authors identified 1 significant SNP after correcting for multiple testing (Bonferroni correction threshold is P < .05/23 ¼ .002).…”

Cellular and molecular maturation in fetal and adult ovine calcaneal tendons

“…Indeed, a higher VA could be essential to support a highly plastic tissue having a very high synthetic activity especially in fetal tendons. Nevertheless, a role for VEGF in sustaining protection and survival of tendon cells in line with the effects recently reported in human tenocytes (Liang et al 2012) and chondrocytes (Maes et al 2012) should not be excluded. Healthy human tenocytes express several VEGF isoforms (Liang et al 2012), and VEGFA mRNA is strongly upregulated following hypoxia under both low-and high-serum conditions.…”

“…Nevertheless, a role for VEGF in sustaining protection and survival of tendon cells in line with the effects recently reported in human tenocytes (Liang et al 2012) and chondrocytes (Maes et al 2012) should not be excluded. Healthy human tenocytes express several VEGF isoforms (Liang et al 2012), and VEGFA mRNA is strongly upregulated following hypoxia under both low-and high-serum conditions. Additionally, VEGF protein released in culture medium increased fourfold by anoxia, exercising a rescue role from cell death (Liang et al 2012).…”

“…Healthy human tenocytes express several VEGF isoforms (Liang et al 2012), and VEGFA mRNA is strongly upregulated following hypoxia under both low-and high-serum conditions. Additionally, VEGF protein released in culture medium increased fourfold by anoxia, exercising a rescue role from cell death (Liang et al 2012).…”

Transient Exposure to Hypoxic and Anoxic Oxygen Concentrations Promotes Either Osteogenic or Ligamentogenic Characteristics of PDL Cells

“…Although this gene is a marker of chondrogenic differentiation, it is known that its expression is also upregulated in tenocytic cells with increased expression of scleraxis . 7 , 16 For chondorogenic differentiation, reoxygenated cells were seeded at concentration of 1×10 6 cells into a 15-mL tube, and cell pellets were cultured in chondrogenic-induction medium (Cat No. PT-3003) supplemented with transforming growth factor β3 (10 ng/mL) (Lonza) for 4 weeks.…”