Expression and secretion of alpha1-proteinase inhibitor are regulated by proinflammatory cytokines in human pancreatic islet cells.
OBJECTIVE
Alpha1-proteinase inhibitor (alpha1-PI) has been considered a key player in inflammatory processes. In humans, the main production site of alpha1-PI is the liver, but other tissues, including pancreatic islets, also synthesise this molecule. The aims of this study were to assess the islet cell types that produce alpha1-PI, to determine whether alpha1-PI is actually secreted by islet cells, and to assess how its production and/or secretion are regulated.


METHODS
Expression of alpha1-PI in human islet cells was assessed by immunofluorescence, electron microscopy and western blotting. Release of alpha1-PI was analysed by reverse haemolytic plaque assay and ELISA. The effects of cytokines on alpha1-PI synthesis and secretion were tested.


RESULTS
Immunofluorescence showed that alpha and delta cells do express alpha1-PI, whereas beta cells do not. By electron microscopy, we demonstrated a colocalisation of alpha1-PI with glucagon and somatostatin within secretory granules. Immunolabelling also revealed localisation of alpha1-PI within the Golgi apparatus, related vesicles and lysosomal structures. The expression of alpha1-PI in islet cells was also demonstrated by western blotting and ELISA of protein extracts. ELISA and reverse haemolytic plaque assay showed that alpha1-PI is secreted into the culture medium. Treatment of islet cells with IL-1beta and oncostatin M for 4 days increased the production and release of alpha1-PI.


CONCLUSIONS
Our results demonstrate that alpha1-PI is expressed by the alpha and delta cells of human islets, and that proinflammatory cytokines enhance the production and release of this inhibitor.
Bosco
Domenico
D
Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals, Switzerland. domenico.bosco@medecine.unige.ch
Meda
Paolo
P
Morel
Philippe
P
Matthey-Doret
David
D
Caille
Dorothée
D
Toso
Christian
C
Bühler
Leo H
LH
Berney
Thierry
T
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D000906:Antibodies / Q000494:pharmacology; D015153:Blotting, Western; D002469:Cell Separation; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005455:Fluorescent Antibody Technique; D006462:Hemolytic Plaque Technique; D006801:Humans; D007150:Immunohistochemistry; D007375:Interleukin-1 / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D000515:alpha 1-Antitrypsin / Q000096:biosynthesis* / Q000235:genetics
D000893:Anti-Inflammatory Agents; D000906:Antibodies; D016207:Cytokines; D007375:Interleukin-1; D000515:alpha 1-Antitrypsin; D003907:Dexamethasone; D015056:1-Methyl-3-isobutylxanthine