cJUN N-terminal kinase (JNK) activation mediates islet amyloid-induced beta cell apoptosis in cultured human islet amyloid polypeptide transgenic mouse islets.
OBJECTIVE
Aggregation of human islet amyloid polypeptide (hIAPP) as islet amyloid is associated with increased beta cell apoptosis and reduced beta cell mass in type 2 diabetes. Islet amyloid formation induces oxidative stress, which contributes to beta cell apoptosis. The cJUN N-terminal kinase (JNK) pathway is a critical mediator of beta cell apoptosis in response to stress stimuli including oxidative stress and exogenous application of hIAPP. We determined whether amyloid formation by endogenous hIAPP mediates beta cell apoptosis through JNK activation and downstream signalling pathways.


METHODS
hIAPP transgenic and non-transgenic mouse islets were cultured for up to 144 h in 16.7 mmol/l glucose to induce islet amyloid in the presence or absence of the amyloid inhibitor Congo Red or a cell-permeable JNK inhibitor. Amyloid, beta cell apoptosis, JNK signalling and activation of downstream targets in the intrinsic and extrinsic apoptotic pathways were measured.


RESULTS
JNK activation occurred with islet amyloid formation in hIAPP transgenic islets after 48 and 144 h in culture. Neither high glucose nor the hIAPP transgene alone was sufficient to activate JNK independent of islet amyloid. Inhibition of islet amyloid formation with Congo Red reduced beta cell apoptosis and partially decreased JNK activation. JNK inhibitor treatment reduced beta cell apoptosis without affecting islet amyloid. Islet amyloid increased mRNA levels of markers of the extrinsic (Fas, Fadd) and intrinsic (Bim [also known as Bcl2l11]) apoptotic pathways, caspase 3 and the anti-apoptotic molecule Bclxl (also known as Bcl2l1) in a JNK-dependent manner.


CONCLUSIONS
Islet amyloid formation induces JNK activation, which upregulates predominantly pro-apoptotic signals in both extrinsic and intrinsic pathways, resulting in beta cell apoptosis.
Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine, VA Puget Sound Health Care System and University of Washington, 1660 South Columbian Way, Seattle, WA 98108, USA.
S L
SL
Subramanian
R L
RL
Hull
S
S
Zraika
K
K
Aston-Mourney
J
J
Udayasankar
S E
SE
Kahn
D000682:Amyloid / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D057898:Hemizygote; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D058228:Islet Amyloid Polypeptide / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D018384:Oxidative Stress / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D046509:Tissue Culture Techniques
D000682:Amyloid; D051017:Apoptosis Regulatory Proteins; D058228:Islet Amyloid Polypeptide; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D048031:JNK Mitogen-Activated Protein Kinases