Islet amyloid accumulates in non-insulin-dependent diabetes mellitus (NIDDM). This amyloid is comprised of islet amyloid polypeptide (IAPP), a normal secretory product of the beta-cell. Transgenic mice expressing the human IAPP (hIAPP) gene and producing the human peptide have been developed to study the mechanism of amyloid formation. The applicant has observed the development of islet amyloid in 81% of the male mice in his colony of hIAPP transgenic mice, often associated with hyperglycemia. This observation was made when the mice were receiving a diet containing an increased proportion of fat (9%). These amyloid deposits contain not only human IAPP, but also apolipoprotein E (apoE) and perlecan, a heparan sulfate proteoglycan. These two constituents are commonly found in other amyloidoses. Based on these observations, he hypothesizes that besides the presence of an amyloidogenic IAPP sequence as occurs with the human form of IAPP, factors such as a high fat diet, hyperglycemia, and apoE are also important for IAPP to deposit as islet amyloid. To address this hypothesis, hIAPP transgenic mice will be studied under conditions of varying dietary fat content controlling for the effect of obesity (6.7% and 24.4%) for periods of 3, 6, and 12 months; hyperglycemia by a) transplantation of islets from hIAPP transgenic mice into hyperglycemic mice and b) crossing hIAPP transgenic mice with heterozygous beta-cell glucokinase knockout mice that develop glucose intolerance; and apoE deficiency by crossing hIAPP transgenic mice with homozygous apoE knockout mice. Islet amyloid accumulation and its constituents will be determined by light and electron microscopy and related to glycemia, plasma lipids, pancreatic mRNA and peptide/protein content. To determine whether beta-cell secretory function and/or IAPP processing from its larger precursor prolAPP is altered in mice studied under the different experimental paradigms associated with islet amyloid formation, pancreas perfusion studies and pulse-chase experiments using isolated islets will be performed. Finally, to examine whether apoE and perlecan are synthesized in islets and what regulates their production, mRNA levels will be measured in isolated islets and pulse-chase experiments will be used to assess protein synthesis in response to fatty acids and glucose.
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