Stimulation of epidermal protein synthesis in vivo by topical triamcinolone acetonide

Measurement of protein metabolism in epidermis and dermis

We found that, in the rabbit ear, the dermal protein contains 75.5% of cutaneous phenylalanine and 97.9% of cutaneous proline; the remaining 24.5% of phenylalanine and 2.1% of proline are in the epidermal protein. This finding led us to develop two novel models that use phenylalanine and proline tracers and the rabbit ear to quantify protein kinetics in the epidermis and dermis. The four-pool model calculates the absolute rates of protein kinetics and amino acid transport, and the two-pool model calculates the apparent rates of protein kinetics that are reflected in the blood. The results showed that both epidermis and dermis maintained their protein mass in the postabsorptive state. The rate of epidermal protein synthesis was 93.4 +/- 37.6 mg x 100 g(-1) x h(-1), which was 10-fold greater than that of the dermal protein (9.3 +/- 5.8 mg x 100 g(-1) x h(-1)). These synthetic rates were in agreement with those measured simultaneously by the tracer incorporation method. Comparison of the four-pool and two-pool models indicated that intracellular cycling of amino acids accounted for 75 and 90% of protein kinetics in the dermis and epidermis, respectively. We conclude that, in the skin, efficient reutilization of amino acids from proteolysis for synthesis enables the maintenance of protein mass in the postabsorptive state.

Protein synthesis and breakdown in skin and muscle: a leg model of amino acid kinetics

In the postabsorptive state, amino acids are released from the periphery to provide precursors for protein synthesis in the splanchnic organs. To evaluate the differential role of the most important peripheral tissues, i.e., skin and muscle, in the interorgan amino acid exchange, we have developed a model to simultaneously measure the rates of protein synthesis and degradation in these tissues. Anesthetized dogs were studied using the arteriovenous catheterization of the leg in combination with muscle and skin biopsies. L-[alpha-15N]lysine and L-[ring-2H5]phenylalanine were infused as independent markers of both skin and muscle protein kinetics. Model structure described leg skin and muscle as tissues arranged in parallel and accounted for blood flow distribution. Lysine data show that, in the postabsorptive state, the fractional rate (%/h) of skin protein synthesis (0.543 +/- 0.218) was comparable to the fractional rate of degradation (0.507 +/- 0.157), whereas, in muscle, degradation (0.454 +/- 0.116) was greater (P < 0.05) than synthesis (0.318 +/- 0.109). Similar conclusions were apparent from the phenylalanine data. Skin protein synthesis and degradation accounted for approximately 10-15% of the total leg protein kinetics.

Hair fibre production by human hair follicles in whole-organ culture

We have used both pulse-chase radiolabelling and morphometric techniques to investigate the ability of whole-organ cultures of human hair follicles to synthesize hair fibre. Anagen hair follicles were obtained from human facial skin by microdissection. Follicles were pulse-labelled with 3H-leucine, and radioactivity in alkali-soluble protein (ASP) and alkali-insoluble hair fibre protein (HFP) fractions was determined by differential extraction. There was a slow decline in ASP radioactivity over 7 days of culture, with a half-life of 4 days. In contrast, leucine incorporation into HFP increased linearly from day 1 to day 5, following an initial delay of 17 h. Morphometric analysis revealed that hair follicles and hair fibres grew at the same rate (0.25 mm/day) for 4 days in culture, after which the rate of hair follicle growth declined progressively, whereas fibre growth continued at the initial rate for a further 3 days. Concurrent with the onset of the decline in follicle growth, the base of the hair fibre began to descend towards the follicle base, until hair fibre occupied almost the full length of the hair follicle at day 15. The decline in follicle growth was preceded by a decline in the rate of follicular 3H-thymidine incorporation, with a delay of approximately 1 day. Overall, these data demonstrate that human hair follicles in whole-organ culture are capable of the production of hair fibre, and suggest that cessation of hair growth in vitro results from depletion of the pool of differentiated follicular keratinocytes, secondary to a loss of matrix cell proliferative activity.