The melanotropic actions of alpha-melanocyte-stimulating hormone (alpha-MSH) and other melanocortins are mediated by activation of the melanocortin 1 receptor (MC1R). This G protein-coupled receptor is positively coupled to Gs and triggers the cyclic adenosine mono-phosphate (cAMP) pathway. Mutations of the MC1R gene are associated with skin type and pigmentation phenotypes, and with increased risk of skin cancers. Genetic studies have demonstrated an heterozygote carrier effect for these associations, suggesting the importance of variant allele dosage. This could be accounted for, at least partially, if the number of MC1R molecules, rather than the Gs protein or the effector enzyme, adenylyl cyclase, is limiting for the activation of the signalling pathway. However, the nature of the limiting factor(s) in MC1R signalling has not been investigated. We addressed this question by comparing the cAMP output of clones of human melanoma cell lines enriched in MC1R by stable transfection. We also analysed heterologous cell systems widely used for functional studies of MC1R. We show that cAMP production in clones of Chinese hamster ovary cells stably expressing the MC1R is a linear function of receptor number up to high, supraphysiological levels of approximately 50,000 alpha-MSH binding sites per cell. Enrichment of human melanoma cell lines with MC1R also results in increased cAMP levels, with a small leftward shift of the agonist dose-response curves. Therefore, at physiological expression levels second-messenger generation is dependent on receptor density. Within melanoma cells and also likely in normal melanocytes, MC1R appears the limiting factor controlling the output of the cAMP signalling pathway.

Objectives: The purpose of this study is to show the preliminary results of using chitosan-based scaffold (BST-CarGel®) with microfracture for treatment of acetabular chondral delamination associated with femoroacetabular impingement. Methods: A prospective study was performed on 13 hips. Patients were selected in the age group between 18 and 50 years. Patients with delamination of acetabular cartilage associated with femoroacetabular impingement received arthroscopic debridement and microfracture technique. Then cases with defect > 2 cm2 were considered for the application of BST-CarGel® and included in the study. Also, reattachment of the torn labrum and resection of the cam deformity were performed according to the case. For evaluation of the functional outcome, the patients had completed the hip outcome score (HOS) pre- and post-operatively. For evaluation of the regeneration of the cartilage, delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) was used and the percentage of defect filling and type of cartilage studied. Results: Patients had a mean age of 41 years, with moderate to high level of activity (mean Tegner scale 7). The mean size of the chondral defect after debridement was 3.7 cm2. The mean HOS for daily live activities has been improved from 64.4 to 87.4 and for sports subscale from 35.2 to 75.2, which is statistically highly significant. All patients had > 90% of filling of chondral defect. Conclusion: The use of BST-CarGel® with microfracture for treatment of acetabular chondral delamination associated with femoroacetabular impingement can improve the functional outcome at two years, with a complete restoration of the cartilage defect in magnetic resonance images (MRI) with specific cartilage sequences.

Microfracture, the current standard of care for the treatment of non-degenerative chondral lesions in the hip joint, is limited by the poor quality of the filling fibrocartilaginous tissue. BST-CarGel (Piramal Life Sciences, Laval, Quebec, Canada) is a chitosan-based biopolymer that, when mixed with fresh, autologous whole blood and placed over the previously microfractured area, stabilizes the blood clot and enhances marrow-triggered wound-healing repair processes. BST-CarGel has been previously applied in the knee, with statistically significant greater lesion filling and superior repair tissue quality compared with microfracture treatment alone. In this report we describe the application of BST-CarGel for the arthroscopic treatment of hip chondral lesions. Our preliminary data suggest that our BST-CarGel procedure provides high-quality repair tissue and therefore may be considered a safe, cost-efficient therapeutic choice for the treatment of hip chondral defects.

No abstract

The a-melanocyte-stimulating hormone (aMSH) receptor (MC1R) is a major determinant of mammalian skin and hair pigmentation. Binding of aMSH to MC1R in human melanocytes stimulates cell proliferation and synthesis of photoprotective eumelanin pigments. Certain MC1R alleles have been associated with increased risk of melanoma. This can be theoretically considered on two grounds. First, gainof-function mutations may stimulate proliferation, thus promoting dysplastic lesions. Second, and opposite, loss-offunction mutations may decrease eumelanin contents, and impair protection against the carcinogenic effects of UV light, thus predisposing to skin cancers. To test these possibilities, we sequenced the MC1R gene from seven human melanoma cell (HMC) lines and three giant congenital nevus cell (GCNC) cultures. Four HMC lines and two GCNC cultures contained MC1R allelic variants. These were the known loss-of-function Arg142His and Arg151Cys alleles and a new variant, Leu93Arg. Moreover, impaired response to a superpotent aMSH analog was demonstrated for the cell line carrying the Leu93Arg allele and for a HMC line homozygous for wild-type MC1R. Functional analysis in heterologous cells stably or transiently expressing this variant demonstrated that Leu93Arg is a loss-of-function mutation abolishing agonist binding. These results, together with site-directed mutagenesis of the vicinal Glu94, demonstrate that the MC1R second transmembrane fragment is critical for agonist binding and maintenance of a resting conformation, whereas the second intracellular loop is essential for coupling to the cAMP system. Therefore, lossof-function, but not activating MC1R mutations are common in HMC. Their study provides important clues to understand MC1R structure-function relationships.