Title:Islet Amyloid Polypeptide (IAPP): A Second Amyloid in Alzheimer's Disease
VOLUME: 11 ISSUE: 10
Author(s):Janelle N. Fawver, Yonatan Ghiwot, Catherine Koola, Wesley Carrera, Jennifer Rodriguez-Rivera, Caterina Hernandez, Kelly T. Dineley, Yu Kong, Jianrong Li, Jack Jhamandas, George Perry and Ian V.J. Murray
Affiliation:Department of Physiology and Neuroscience, PO-Box 7, St George's University, St Georges, Grenada, West Indies.
Keywords:Alzheimer's disease, amyloid beta, amylin, blood, brain, immunohistochemistry, metabolic dysfunction, oligomers,
plaques, type 2 diabetes.
Abstract:Amyloid formation is the pathological hallmark of type 2 diabetes (T2D) and Alzheimer’s disease (AD). These
diseases are marked by extracellular amyloid deposits of islet amyloid polypeptide (IAPP) in the pancreas and amyloid β
(Aβ) in the brain. Since IAPP may enter the brain and disparate amyloids can cross-seed each other to augment amyloid
formation, we hypothesized that pancreatic derived IAPP may enter the brain to augment misfolding of Aβ in AD. The
corollaries for validity of this hypothesis are that IAPP [1] enters the brain, [2] augments Aβ misfolding, [3] associates
with Aβ plaques, and most importantly [4] plasma levels correlate with AD diagnosis. We demonstrate the first 3 corollaries
that: (1) IAPP is present in the brain in human cerebrospinal fluid (CSF), (2) synthetic IAPP promoted oligomerization
of Aβ in vitro, and (3) endogenous IAPP localized to Aβ oligomers and plaques. For the 4 corollary, we did not observe
correlation of peripheral IAPP levels with AD pathology in either an African American cohort or AD transgenic mice. In
the African American cohort, with increased risk for both T2D and AD, peripheral IAPP levels were not significantly different
in samples with no disease, T2D, AD, or both T2D and AD. In the Tg2576 AD mouse model, IAPP plasma levels
were not significantly elevated at an age where the mice exhibit the glucose intolerance of pre-diabetes. Based on this
negative data, it appears unlikely that peripheral IAPP cross-seeds or “infects” Aβ pathology in AD brain. However, we
provide novel and additional data which demonstrate that IAPP protein is present in astrocytes in murine brain and secreted
from primary cultured astrocytes. This preliminary report suggests a potential and novel association between brain
derived IAPP and AD, however whether astrocytic derived IAPP cross-seeds Aβ in the brain requires further research.
