title: Replication increases beta-cell vulnerability to human islet amyloid polypeptide-induced apoptosis.
abstract: Type 2 diabetes is characterized by a relative beta-cell deficit as a result of increased beta-cell apoptosis and islet amyloid derived from the beta-cell peptide islet amyloid polypeptide (IAPP). Human IAPP (h-IAPP) but not mouse IAPP (m-IAPP) induces apoptosis when applied to cells in culture, a property that depends on the propensity of h-IAPP to oligomerize. Since beta-cell mass is regulated, the question arises as to why it is not adaptively increased in response to insulin resistance and hyperglycemia in type 2 diabetes. This adaptation might fail if dividing beta-cells preferentially underwent apoptosis. We tested the hypothesis that beta-cells are preferentially vulnerable to h-IAPP-induced apoptosis. We established a microculture environment to perform time-lapse video microscopy (TLVM) and studied beta-cells (RIN) and HeLa cells undergoing replication or apoptosis. Sequential images (every 10 min for 36 h in RIN or 24 h in HeLa cells) of cells in vivo were analyzed, and each mitotic and apoptotic event was documented. Freshly dissolved h-IAPP caused a dose-dependent increased rate of apoptosis (P < 0.0001) in both cell types. At low and medium levels of toxicity, cells that had previously undergone mitosis were more vulnerable to h-IAPP-induced apoptosis than nondividing cells (P < 0.05). In the first 3 h after mitosis (full cell cycle length 26 +/- 0.6 h), beta-cells were particularly susceptible to h-IAPP-induced apoptosis (P < 0.05). Neither m-IAPP nor mature amyloid aggregates of h-IAPP were cytotoxic (P = 0.49). To corroborate these cell culture studies, we examined sections of human pancreatic tissue (five cases of type 2 diabetes) and human islets incubated for 48 h +/- h-IAPP. Both were stained for apoptosis with the transferase-mediated dUTP nick-end labeling method and analyzed for the presence of paired apoptotic cells anticipated in the event of postmitotic apoptosis. In human pancreatic tissue 26 +/- 5% (single plane of examination) and in human islets incubated with h-IAPP 44 +/- 4% of apoptotic islet cells were paired. In conclusion, replicating beta-cells are preferentially vulnerable to h-IAPP-induced apoptosis in cell culture. Postmitotic apoptosis was also documented in humans with type 2 diabetes and in human islet tissue. We postulate that beta-cell deficiency in type 2 diabetes may result in part from failure to adaptively increase beta-cell mass due to increased vulnerability of replicating beta-cells to undergo apoptosis. If this postulate is correct, then inhibition of apoptosis should allow recovery of beta-cell mass in type 2 diabetes.
authors.affiliation: Division of Endocrinology and Diabetes, Keck School of Medicine, University of Southern California, Los Angeles 90033, USA. ritzel@usc.edu
authors.forename: Robert A
authors.initials: RA
authors.lastname: Ritzel
authors.forename: Peter C
authors.initials: PC
authors.lastname: Butler
mesh_terms: D000682:Amyloid / Q000494:pharmacology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D048429:Cell Size / Q000187:drug effects; D003924:Diabetes Mellitus, Type 2 / Q000473:pathology / Q000503:physiopathology; D006367:HeLa Cells; D006801:Humans; D058228:Islet Amyloid Polypeptide; D007515:Islets of Langerhans / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018715:Microscopy, Video; D008938:Mitosis / Q000187:drug effects
chemical_list: D000682:Amyloid; D058228:Islet Amyloid Polypeptide