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Regulated laminin-332 expression in human islets of Langerhans

Mathieu Armanet^*, Anne Wojtusciszyn^*,1, Philippe Morel^*, Géraldine Parnaud^*, Patricia Rousselle, Corinne Sinigaglia^*, Thierry Berney^* and Domenico Bosco^*,2

^* Department of Surgery, Cell Isolation and Transplantation Center, Geneva University Hospitals and University of Geneva, Geneva, Switzerland; and

Institut de Biologie et Chimie des Protéines, CNRS et Université Lyon-1, Lyon, France

² Correspondence: Department of Surgery, Cell Isolation and Transplantation Center, Geneva University Hospitals and University of Geneva, 1211 Geneva-4, Switzerland. E-mail: domenico.bosco{at}unige.ch

Laminin-332 (LN-332) is a basement membrane component known to exert a beneficial effect on rat pancreatic β cells in vitro. In this work, we analyzed the expression of LN-332 in human islets, its expression after inflammatory insults by cytokines, and the molecular mechanisms responsible for this effect. By Western blotting and RT-PCR, we showed that LN-332 was expressed in isolated human islets. By immunofluorescence on pancreas sections, we observed that labeling was confined to endocrine cells in islets. Confocal microscopy analysis on isolated islet cells revealed that labeling was granular but did not colocalize with hormone secretory granules. LN-332 was most abundant in cultured islets compared to freshly isolated islets and was found in culture medium, which suggests that it was secreted by islets. When islets were exposed to interleukin (IL)-1β, expression and secretion of LN-332 increased as compared to control. No effect was observed with tumor necrosis factor (TNF)- and interferon (IFN)-. LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3-K) activity, inhibited culture- and IL-1β-induced LN-332 expression in islets. These results show that LN-332, known to have some beneficial effect on β cells in vitro, is produced and secreted by endocrine islet cells and is up-regulated by stressing conditions such as culture and IL-1β-exposure.—Armanet, M., Wojtusciszyn, A., Morel, P., Parnaud, G., Rousselle, P., Sinigaglia, C., Berney, T., Bosco, D. Regulated laminin-332 expression in human islets of Langerhans.

Key Words: extracellular matrix • cytokines • PI3-K