The role of caspase-8 in amyloid-induced beta cell death in human and mouse islets.
OBJECTIVE
Reduced beta cell mass due to increased beta cell apoptosis is a key defect in type 2 diabetes. Islet amyloid, formed by the aggregation of human islet amyloid polypeptide (hIAPP), contributes to beta cell death in type 2 diabetes and in islet grafts in patients with type 1 diabetes. In this study, we used human islets and hIAPP-expressing mouse islets with beta cell Casp8 deletion to (1) investigate the role of caspase-8 in amyloid-induced beta cell apoptosis and (2) test whether caspase-8 inhibition protects beta cells from amyloid toxicity.


METHODS
Human islet cells were cultured with hIAPP alone, or with caspase-8, Fas or amyloid inhibitors. Human islets and wild-type or hIAPP-expressing mouse islets with or without caspase-8 expression (generated using a Cre/loxP system) were cultured to form amyloid. Caspase-8 and -3 activation, Fas and FLICE inhibitory protein (FLIP) expression, islet beta cell and amyloid area, IL-1β levels, and the beta:alpha cell ratio were assessed.


RESULTS
hIAPP treatment induced activation of caspase-8 and -3 in islet beta cells (via Fas upregulation), resulting in apoptosis, which was markedly reduced by blocking caspase-8, Fas or amyloid. Amyloid formation in cultured human and hIAPP-expressing mouse islets induced caspase-8 activation, which was associated with Fas upregulation and elevated islet IL-1β levels. hIAPP-expressing mouse islets with Casp8 deletion had comparable amyloid, IL-1β and Fas levels with those expressing hIAPP and Casp8, but markedly lower beta cell apoptosis, higher beta:alpha cell ratio, greater beta cell area, and enhanced beta cell function.


CONCLUSIONS
Beta cell Fas upregulation by endogenously produced and exogenously applied hIAPP aggregates promotes caspase-8 activation, resulting in beta cell apoptosis. The prevention of amyloid-induced caspase-8 activation enhances beta cell survival and function in islets.
Department of Surgery, Faculty of Medicine, University of British Columbia, Jim Pattison Pavilion, Vancouver General Hospital, 910 W 10th Ave., Vancouver, BC, Canada, V5Z 4E3.
Yoo Jin
YJ
Park
Minna
M
Woo
Timothy J
TJ
Kieffer
Razqallah
R
Hakem
Nooshin
N
Safikhan
Fan
F
Yang
Ziliang
Z
Ao
Garth L
GL
Warnock
Lucy
L
Marzban
D000328:Adult; D000682:Amyloid / Q000633:toxicity*; D000818:Animals; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000201:enzymology*; D007515:Islets of Langerhans / Q000166:cytology*; D008297:Male; D051379:Mice; D008875:Middle Aged
D000682:Amyloid; D053148:Caspase 3; D053181:Caspase 8