Differential effects of oxygen on human dermal fibroblasts: acute versus chronic hypoxia

Abstract

The observation that many chronic wounds are ischemic has spurred a series of studies evaluating the response of cells exposed to hypoxia. To date, these studies have shown largely beneficial effects from hypoxia, such as increased cellular replication and procollagen synthesis. These findings are counter-intuitive from a clinical standpoint because cellular growth and synthetic function are known to be retarded in chronic ischemic wounds. We have established an in vitro system in which human dermal fibroblasts grown chronically at 5 +/- 3 mm Hg will proliferate at a rate three times slower than those fibroblasts grown under standard culture conditions (namely an oxygen partial pressure of 150 mm Hg). No phenotypic changes are noted in chronically hypoxic cells, and the growth-retarding effects are reversible when the cells are returned to standard oxygen conditions. Competitive reverse transcription-polymerase chain reaction showed that acute exposure to hypoxia (up to 1 week) results in a 6.3-fold increase in the relative expression of transforming growth factor-beta1 messenger RNA, whereas chronic exposure to hypoxia leads to a 3.1-fold decrease in this message. Collagen production measured at both the mRNA and protein level is also decreased in the setting of chronic hypoxia. We propose that this system may be the most appropriate setting for studying the role of oxygen on dermal fibroblasts in ischemic, nonhealing wounds.

Oxygen in wound healing: More than a nutrient

“…After 72 hours exposure to 1% oxygen, the proliferative rate of fibroblasts increases by 71% [10]. Low oxygen tensions have been shown to initiate clonal expansion of fibroblasts [18], a finding that would be surprising if only the previously made statements in this review were taken into account.…”

“…In vitro it has been shown that human dermal fibroblasts decrease their proliferative activity under chronic hypoxia (six passages at 1% O 2 ) [10]. In vivo oxygen tissue tensions of nearly 5-15 mmHg were measured at the threshold between the epicenter of the wound and granulation tissue where leukocytes (mainly macrophages) were most commonly seen.…”

Modelling the interaction of keratinocytes and fibroblasts during normal and abnormal wound healing processes

“…Prolonged hypoxia is one of the most common causes of chronic wounds [32], where healing fails to produce anatomical and functional integrity [33]. Siddiqui et al [86] noted that fibroblast cells placed in chronically low oxygen levels over 72 h exhibited a 50 per cent decrease in population doublings, a 1.48-fold reduction in collagen production and a 3.1-fold decrease in TGF-b production relative to a standard oxygen system. These observations confirm the findings that chronic hypoxia reduces collagen production and that fibroblast proliferation is greatly inhibited in this case [87].…”

Provisional Matrix Deposition in Hemostasis and Venous Insufficiency: Tissue Preconditioning for Nonhealing Venous Ulcers

“…However, exposure to prolonged culture in hypoxic conditions ( > 1 week), thus, mimicking an ischemic dermal environment, did not support these processes. 112 Similarly, other studies using dermal fibroblasts have reported up-regulated expression of pro-a1 (I) 113 and (III) collagens 114,115 after acute exposure to hypoxic conditions in vitro, followed by decreased expression in response to prolonged hypoxia. 114,115 Under hypoxic conditions dermal fibroblastproduced collagen cannot be synthesized or crosslinked effectively, since the enzymes required for collagen polymerization and crosslinking, prolyl hydroxylase, lysyl hydroxylase, and lysyl oxidase, all require molecular oxygen as a cofactor to perform their biological function in the collagen synthesis and maturation pathway.…”