Introduction to the themed issue on the biology of UVA

Well before the discovery of the genetic code it was shown that the action spectrum for the killing of Escherichia coli corresponded closely with the peak for DNA absorption (F. L. Gates, J. Gen. Physiol., 1930, 14, 31–42), and this and similar observations led to the eventual emphasis and understanding of the importance of the DNA absorbing UVB region of the solar spectrum. Interestingly, Alexander Hollaender (J. Bacteriol., 1943, 46, 531–541) had also made the interesting observation nearly 70 years ago that bacteria exposed to UVA became salt-sensitive, implying a distinct membrane damaging role of the longer wavelengths many years before the key role of UVA in damaging lipids was recognised. There was then relatively little interest in UVA effects until the late 1960s when Abe Eisenstark and particularly Bob Webb's group at Argonne National Laboratory published details of additional work showing the uniqueness of the biological response to UVA, findings that were enthusiastically built on in subsequent years by one of the co-editors. Although the field still grew slowly over the next few years, it became clearly established that UVA generated an oxidative stress in cells and tissues, and in the early 1990s IARC Monograph 55 recognised UVA as a probable human carcinogen.

Over the next two decades, interest and publications in the UVA field grew substantially and the last 10 years has witnessed many advances in our understanding of this crucial region of the solar spectrum. This issue dedicated to UVA contains several in-depth perspectives and original articles in the field highlighting key advances. There has been intense activity in understanding the range of DNA damage caused by UVA (Mouret et al., DOI: 10.1039/c1pp05185g; Epe, DOI: 10.1039/c1pp05190c) and the biological consequences including mutagenesis (perspective by Sage et al., DOI: 10.1039/c1pp05219e). Indeed several articles (Mitchell and Fernandez, DOI: 10.1039/c1pp05146f; Rünger et al., DOI: 10.1039/c1pp05232b; Pfeifer and Besaratinia, DOI: 10.1039/c1pp05144j; Chen et al., DOI: 10.1039/c1pp05197k) address the link between UVA-induced DNA damage, mutagenesis and cancer, particularly melanoma. A further article describes current knowledge on the epidemiology of melanoma in Scandinavia (Moan et al., DOI: 10.1039/c1pp05215b) and the perspective by Doré and Chignol (DOI: 10.1039/c1pp05186e) provides current thinking on the strong link between deliberate tanning in sun salons and skin cancer. Given the evident need for protection against UVA, it is pertinent that Fourtanier et al. (DOI: 10.1039/c1pp05152k) describe UVA filters that are currently being harnessed for this purpose.

Tewari et al. (DOI: 10.1039/c1pp05243h) explore the link between human erythema and matrix metalloproteinase-1 induction, suggesting that they have common chromophores, one of which is DNA. In general, both protein and lipids take on a much larger role as critical targets of UVA radiation in contrast to the central role of DNA in UVB effects. A thorough review of the multiple changes induced in amino acids and proteins by UVA is provided by Pattison et al. (DOI: 10.1039/c1pp05164d). Both protein and lipid damage can be mediated via singlet oxygen generated by UVA from endogenous sensitisers and Bäumler (DOI: 10.1039/c1pp05142c) presents a state of the art perspective on its measurement by luminescence. Iron is also crucially involved in the generation of reactive oxygen species and UVA damage and a perspective on the role of iron in UVA radiation biology is provided in the review by Aroun et al. (DOI: 10.1039/c1pp05204g). One of the consequences of iron involvement is lysosomal destruction by UVA and the article by Lamore and Wondrak (DOI: 10.1039/c1pp05131h) provides new insights into the role of proteases and impaired autophagic flux in this process. Oxygen-dependent damage to membrane lipids appears to be central to some of the biological consequences of UVA and, importantly, UVA-generated lipid messengers are likely to be involved in the activation of a plethora of genes (see perspective by Tyrrell, DOI: 10.1039/c1pp05222e) including those involved in inflammation, matrix remodelling and eventually photodegradation (via metalloproteinases). The signal transduction processes (particularly p38 MAP kinases and JNK) that underlie the modulation of gene expression by UVA are considered in greater depth in the perspective by Zhang and Bowden (DOI: 10.1039/c1pp05133d).

In rodent models, recent studies have revealed gender differences in immune responses and interestingly this has now been linked to male unresponsiveness to UVA radiation (Reeve et al., DOI: 10.1039/c1pp05224a). At the clinical level, UVA appears to be involved in various pathologies and several aspects of this are considered in the overview by Smith et al. (DOI: 10.1039/c1pp05191a). Finally observations on the incorporation of photosensitising nucleic acids in DNA is opening up new avenues for photochemotherapy (Reelfs et al., DOI: 10.1039/c1pp05188a) but may also inadvertently generate skin cancer complications in organ transplant patients, as highlighted in the article by Attard and Karran (DOI: 10.1039/c1pp05194f)

This UVA themed issue project quickly generated considerable enthusiasm and effort to provide diverse contributions and we are confident that this effort will provide an interesting and comprehensive journey through the UVA field for readers of the journal, even those for whom this particular area is less familiar.

 

Evelyn Sage and Rex Tyrrell

Co-editors

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