Replication Increases β-Cell Vulnerability to Human Islet Amyloid Polypeptide-Induced Apoptosis

• Published in: Diabetes (New York, N.Y.) Vol. 52; no. 7; pp. 1701 - 1708
• Main Authors: RITZEL, Robert A, BUTLER, Peter C
• Format: Journal Article
• Language: English
• Published: Alexandria, VA American Diabetes Association 01.07.2003
• Subjects: Amyloid - pharmacology; Animals; Apoptosis - drug effects; Apoptosis - physiology; Biological and medical sciences; Cell Division - physiology; Cell Line; Cell Size - drug effects; Diabetes Mellitus, Type 2 - pathology; Diabetes Mellitus, Type 2 - physiopathology; Fundamental and applied biological sciences. Psychology; HeLa Cells; Humans; Islet Amyloid Polypeptide; Islets of Langerhans - cytology; Islets of Langerhans - drug effects; Islets of Langerhans - physiology; Mice; Microscopy, Video; Mitosis - drug effects
• ISSN: 0012-1797; 1939-327X
• DOI: 10.2337/diabetes.52.7.1701

Replication Increases β-Cell Vulnerability to Human Islet Amyloid Polypeptide-Induced Apoptosis Robert A. Ritzel and Peter C. Butler From the Division of Endocrinology and Diabetes, Keck School of Medicine, University of Southern California, Los Angeles, California Address correspondence and reprint requests to Robert A. Ritzel, Division of Endocrinology and Diabetes, Keck School of Medicine, University of Southern California, 1333 San Pablo St., BMT-B11, Los Angeles, CA 90033. E-mail: ritzel{at}usc.edu Abstract Type 2 diabetes is characterized by a relative β-cell deficit as a result of increased β-cell apoptosis and islet amyloid derived from the β-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 β-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 β-cells preferentially underwent apoptosis. We tested the hypothesis that β-cells are preferentially vulnerable to h-IAPP-induced apoptosis. We established a microculture environment to perform time-lapse video microscopy (TLVM) and studied β-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), β-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 β-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 β-cell deficiency in type 2 diabetes may result in part from failure to adaptively increase β-cell mass due to increased vulnerability of replicating β-cells to undergo apoptosis. If this postulate is correct, then inhibition of apoptosis should allow recovery of β-cell mass in type 2 diabetes. IAPP, islet amyloid polypeptide h-IAPP, human IAAP m-IAPP, mouse IAPP TLVM, time-lapse video microscopy TUNEL, transferase-mediated dUTP nick-end labeling Footnotes Accepted March 24, 2003. Received November 20, 2002. DIABETES