In vivo Expression of the Collagen-Related Heat Shock Protein HSP47, Following Hyperthermia or Photodynamic Therapy
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Heat shock protein 47 (HSP 47), a molecule expressed constitutively in cells that synthesise collagen, is involved in collagen type I biosynthesis, and after insult acts as a stress response molecule to sequester abnormal procollagen. Photodynamic therapy (PDT) is claimed not to result in extensive collagen damage, such as that which can occur after other laser treatments, e.g. hyperthermia (HT) or coagulation, thereby conferring on PDT a potential therapeutic advantage. In previous studies on mouse fibroblasts in vitro we demonstrated HSP47 elevation in the first hours after the application of conditions known to damage collagen, and an absence of HSP47 elevation following PDT with two well-established photosensitisers, haematoporphyrin ester (HpE) and meta-tetrahydroxyphenylchlorin (mTHPC).
The present study examines HSP47 metabolism in murine skin following (1) HT, (2) PDT with HpE and (3) PDT with riboflavin (RB). Riboflavin was examined because of reports of collagen injury induced by its photoactivation. All three stresses were applied at grossly equitoxic, ‘tolerance’ doses. Three months after these doses, linear extensometry revealed the skin to have fibrotic characteristics after HT and RB PDT, but not after HpE PDT. HSP47 expression levels were analysed at transcriptional (Northern) and translational (Western) levels at early time intervals up to 24 h after the treatment application, starting immediately after the treatment for mRNA and 6 h post-treatment for protein. Highly significant upregulation of HSP47 was detected following HT, and PDT with RB. PDT mediated by HpE did not have any impact on HSP47 levels. These results were thus consistent with those from in vitro work and support the hypothesis of early elevation of HSP47 expression only by modalities affecting collagen or its precursors.
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