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.
Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals, Switzerland. domenico.bosco@medecine.unige.ch
Domenico
D
Bosco
Paolo
P
Meda
Philippe
P
Morel
David
D
Matthey-Doret
Dorothée
D
Caille
Christian
C
Toso
Leo H
LH
Bühler
Thierry
T
Berney
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