Ageing results in skin which may be more fragile and dry, clinical features which could be due to changes in molecular water homeostasis. Possible regulatory mechanisms are thought to be related to the transport of organic osmolytes, which not only maintain cellular water content but can also can act as antioxidants and assist in protein stabilisation to counteract damage. Therefore, we aimed to characterise osmolyte transporter expression in human skin and to investigate how these may alter with intrinsic and extrinsic ageing. Skin samples were collected from photoprotected buttock and photoexposed forearm of young (18-30 years; n=5) and aged (>65 year; n=6) healthy volunteers. In a second cohort, healthy volunteers (18-30 years; n=5) were subjected to acute solar-simulated radiation (SSR; 8SED) with biopsies taken at baseline (unirradiated) and +1, +3 and +72 hours post-irradiation. Expression of taurine transporter (TAUT), betaine transporter (BGT-1) and myoinositol transporter (HMIT) were assessed via immunofluorescence. Taurine transporter was expressed the epidermis of photoprotected skin; its expression did not change with intrinsic ageing. However, in chronically photoexposed skin, TAUT expression was significantly decreased (P=0.04). Expression of BGT-1 and HMIT were not significantly altered with intrinsic or extrinsic skin ageing. Following SSR, TAUT protein expression at +1 and +3 hours post-SSR was unchanged. However, by +72 hours post-SSR there was ~50% reduction in epidermal expression of TAUT (P=0.01). Here, we characterise the unique expression patterns of organic osmolyte transporters TAUT, BGT-1 and HMIT in human skin. Our results demonstrate for the first time that chronic UV exposure results in decreased TAUT protein expression in skin and indicates that taurine transport may be fundamental in the pathophysiology of skin photoageing and could be considered as a novel therapeutic target.

Taurine transporter, TAUT, is significantly down-regulated in photoexposed human skin