Project description:Ultraviolet A (UVA) radiation is the major fraction of UV radiation reaching the Earth’s surface; its harmful effects on microorganisms obey mainly to oxidative damage, with the consequent loss of bacterial viability. In this work, the global transcriptional response of Pseudomonas aeruginosa exposed to UVA was analyzed. P. aeruginosa is an opportunistic human pathogen, also present in terrestrial and aquatic environments; its high ubiquity and versatily obeys to a complex regulatory network wich allows it to adapt to stressful conditions. To conduct this study, the PAO1 strain was grown in under sublethal doses of UVA or in the dark up to early logarithmic phase, and total RNA was obtained and sequenced by the RNA-seq technique. The analysis of the results, taking as significant a factor change ≥ 2 between irradiated and control samples, indicated that a total of 298 genes were regulated by UVA, representing 5.36 % of the total P. aeruginosa genome; half of these were induced and the other half were repressed. Data obtained by the transcriptomic study were validated by using RT qPCR of selected genes. The results presented in this study suggest that one of the main UVA targets are proteins carrying [Fe-S] clusters since several genes involved in the processes of synthesis, trafficking and assembly of these structures were upregulated. The management of intracellular iron levels also seems to be a robust response to this stress factor. The strong induction of genes involved in denitrification led us to suggest that this pathway and/or reactive nitrogen species such as nitric oxide could have a role in the response to this radiation. DNA also demonstrated to be an important UVA target as observed by the induction of SOS, prohage and pyocins genes. On the other hand, the down-regulation of genes involved in the biosynthesis of PQS, a quorum sensing signal of P. aeruginosa with several functions, could be beneficial given its role as endogenous photosensitizer. The study of the effects of UVA radiation is interesting due to its ecological consequences in natural environments. In addition, taking into account the high sensitivity of P.aeruginosa to UVA radiation and the issues with using traditional antibacterial products by the intrinsec or acquired resistance of P. aeruginosa to these agents, specially in the case of biofilms, UVA studies could have important implications for human health, industrial facilities and environmental management.

Project description:Ultraviolet (UV) wavebands in sunlight are immunomodulatory. About half the amount of UVA within a minimum erythemal dose of sunlight is systemically immunosuppressive, while higher doses protect from UVB immunosuppression in mice. We have previously shown that these responses to UVA are genetically restricted as they occur in C57BL/6 but not Balb/c mice. We used gene set enrichment analysis of microarray data and real-time RT-PCR confirmation to determine the molecular mechanisms associated with UVA immunomodulation. We found up-regulation of mRNA for the alternative complement pathway. The core-enriched genes complement component 3, properdin and complement factor B were all activated by the immunosuppressive dose of UVA only in UVA-responsive C57BL/6 but not unresponsive BALB/c mice. This therefore matched the genetic restriction and dose responsiveness of UVA immunosuppression. The immune-protective higher UVA dose prevented UVB from down regulating chemokine receptor 7 and IL-12B, and decreased IL-10, supporting previous identification of IL-12 and IL-10 in high dose UVA protection from UVB immunosuppression. Our study has identified activation of the alternative complement pathway as a trigger of UVA-induced systemic immunosuppression and suggests that this pathway is likely to be an important sensor of UVA-induced damage to the skin. 24 hours after UVA, UVB and ssUV irradiation, a 1 cm2 uniform section of skin was excised from the dorsal surface of irradiated and control mice. Total RNA was then extracted from the whole skin using TRIzol reagent (Gibco Invitrogen Life Technologies, Carlsbad, CA, USA) according to the manufacturerâ??s instructions, purified, DNase treated and reverse transcribed into cDNA. For the microarray study a direct incorporation of Cyanine 3-dCTP and Cyanine 5-dCTP fluorescent dyes (Perkin Elmer Life Sciences, Inc. Boston, MA, USA) was used for cDNA synthesis. For each UV dose, a reference design was used to compare an unirradiated control against an irradiated sample. Microarray experiments used compugen 22k mouse oligonucleotide microarray slides (The Clive and Vera Ramaciotti Centre for Gene Function Analysis, Sydney Australia (http://www.ramaciotti.unsw.edu.au). Lower and higher UVA doses were used. C57BL/6 mice were irradiated with lower UVA, higher UVA, UVB, or ssUV; Balb/C mice were irradiated with lower or higher UVA. Experiments were replicated 6 times for each UV dose. A fluorescent dye swap was done for each alternate hybridisation to reduce systematic dye bias of incorporated fluorescent dyes.

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DrRibUvac

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