Hyperpigmentation in human solar lentigo is promoted by heparanase-induced loss of heparan sulfate chains at the dermal-epidermal junction.

BACKGROUND: Skin pigmentation induced by ultraviolet B radiation is caused in part by inflammation mediated by cytokines secreted from keratinocytes and fibroblasts in the irradiated area. Heparanase is also activated in the irradiated skin, and this leads to loss of heparan sulfate at the dermal-epidermal junction (DEJ), resulting in uncontrolled diffusion of heparan sulfate-binding cytokines through the DEJ. However, it is not clear whether heparanase-induced loss of heparan sulfate at the DEJ is involved in the pigmentation process in sun-exposed skin. OBJECTIVE: We examined the role of heparan sulfate in the pigmentation process of human pigmented skin and in pigmented skin-equivalent model. METHODS: Heparan sulfate and blood vessels in human pigmented skin, solar lentigo, and non-pigmented skin were evaluated by means of immunohistochemistry. Pigmented skin equivalent models were cultured with or without heparanase inhibitor and the pigmentation levels were compared. RESULTS: In solar lentigo, heparan sulfate was hardly observed, presumably due to the increase of heparanase at the DEJ, in spite of the deposition of core protein of perlecan (also known as heparan sulfate proteoglycan). The number of blood vessels was significantly increased in solar lentigo. In the pigmented skin equivalent model, heparanase inhibitor increased the staining intensity of heparan sulfate at the DEJ and markedly reduced melanogenesis in the epidermis. CONCLUSIONS: Our results indicate that heparanase-induced loss of heparan sulfate at the DEJ is involved in the pigmentation process of human skin. Consequently, heparanase inhibitors can be expected to exert a protective effect against ultraviolet exposure-induced skin pigmentation.

Evidence that PKA activity is constitutively activated in human GH-secreting adenoma cells in a patient with Carney complex harbouring a PRKAR1A mutation.

CONTEXT: The GHRH-protein kinase A (PKA) signalling pathway is essential for cell proliferation and GH synthesis/secretion in somatotrophs. An inactivating mutation of PRKAR1A is one of the causes of somatotrophinoma in Carney complex (CNC). The basal PKA activity of somatotroph adenoma cells from CNC has not been evaluated because of a limited amount of available tissue. OBJECTIVE: This study examined how the PRKAR1A mutation affects the PKA signalling pathway in a human somatotrophinoma with a PRKAR1A mutation. DESIGN AND SETTING: Somatotrophinoma cells from a 40-year-old male patient with CNC were used. The patient had a novel somatic heterozygous germline frameshift mutation (227delT) in PRKAR1A leading to a premature stop codon. The tumour showed loss of heterozygosity (LOH) at 17q23-24. Primary cultured adenoma cells were subjected to electrophysiological experiments to evaluate PKA signalling in individual cells. RESULTS: GHRH did not increase the nonselective cation current or the voltage-gated calcium current in these adenoma cells, in contrast to nonadenomatous somatotroph cells in which these currents increase through the PKA pathway. Application of a PKA inhibitor inhibited the basal currents in these adenoma cells, results that were not observed in nonadenomatous somatotrophs. These data indicate that the basal currents are already increased and cannot be further increased by GHRH. CONCLUSIONS: The results demonstrate that PKA is activated at the basal state in these adenoma cells. The data also show that both the nonselective cation current and the voltage-gated calcium current, vital regulators of GH secretion downstream of PKA, are maximally increased in these cells. These maximally increased currents probably account for the excessive GH secretion.