Age-Dependent Decline in β-Cell Proliferation Restricts the Capacity of β-Cell Regeneration in Mice

ObjectiveThe aim of this study was to elucidate whether age plays a role in the expansion or regeneration of beta-cell mass.Research design and methodsWe analyzed the capacity of beta-cell expansion in 1.5- and 8-month-old mice in response to a high-fat diet, after short-term treatment with the glucagon-like peptide 1 (GLP-1) analog exendin-4, or after streptozotocin (STZ) administration.ResultsYoung mice responded to high-fat diet by increasing beta-cell mass and beta-cell proliferation and maintaining normoglycemia. Old mice, by contrast, did not display any increases in beta-cell mass or beta-cell proliferation in response to high-fat diet and became diabetic. To further assess the plasticity of beta-cell mass with respect to age, young and old mice were injected with a single dose of STZ, and beta-cell proliferation was analyzed to assess the regeneration of beta-cells. We observed a fourfold increase in beta-cell proliferation in young mice after STZ administration, whereas no changes in beta-cell proliferation were observed in older mice. The capacity to expand beta-cell mass in response to short-term treatment with the GLP-1 analog exendin-4 also declined with age. The ability of beta-cell mass to expand was correlated with higher levels of Bmi1, a polycomb group protein that is known to regulate the Ink4a locus, and decreased levels of p16(Ink4a)expression in the beta-cells. Young Bmi1(-/-) mice that prematurely upregulate p16(Ink4a)failed to expand beta-cell mass in response to exendin-4, indicating that p16(Ink4a)levels are a critical determinant of beta-cell mass expansion.Conclusionsbeta-Cell proliferation and the capacity of beta-cells to regenerate declines with age and is regulated by the Bmi1/p16(Ink4a)pathway

Beneficial effects of parenteral GLP-1 delivery by cell therapy in insulin-deficient streptozotocin diabetic mice.

Parenteral delivery of long-Acting glucagon-like peptide-1 (GLP-1) mimetics has received much attention as a therapeutic option for diabetes. However, cell therapy-based GLP-1 treatments may provide a more physiological regulation of blood glucose. The present study assessed the effects of chronic GLP-1 delivery by cell therapy, using the GLP-1-secreting GLUTag cell line, in normoglycemic and streptozotocin-induced diabetic mice. GLUTag cell aggregates were transplanted into the subscapular region of mice. Over 30 days, cellular transplantation gave rise to encapsulated and well-vascularized growths, which contained immunoreactive GLP-1. Cell implantation was well tolerated and had no appreciable metabolic effects in normal mice. However, transplantation significantly (P<0.001) countered excessive food and fluid intake in diabetic mice and maintained normal body weight. Circulating glucose (P<0.01) and glucagon (P<0.05) were significantly reduced and plasma insulin and GLP-1 dramatically increased. This was associated with significantly (P<0.01) improved glucose tolerance in diabetic mice. Histological examination of the pancreata of these mice revealed elevations (P<0.001) in islet and β-cell area, with reduced (P<0.001) -cell area. Increased β-cell mass reflected the enhanced proliferation relative to apoptosis. These studies emphasize the potential of chronic GLP-1 delivery by cell therapy as a potential therapeutic option for diabetes

Familial Cutaneous Lichen Amyloidosis in Association with Multiple Endocrine Neoplasia Type 2A: A New Variant

Multiple endocrine neoplasia type 2A (MEN 2A) is a rare hereditary disease transmitted in families as an autosomal dominant trad. We have identified a family in which the expression of a rare autosomal dominant form of cutaneous lichen amyloidosis appears to cosegregate with MEN 2A. In this family the skin lesion presented as multiple infiltrated papules overlying well demarcated plaques over the scapular area (right or left). Immunohistochemical studies demonstrated amyloid which stained for keratin but not calcitonin. A total of 19 members were screened. Three members of the family have the characteristic skin lesion and MEN 2A; two additional members have MEN 2A but have not manifested observable skin changes of lichen amyloidosis. Another unrelated Italian family with a similar type of pruritic skin rash and MEN 2A has been reported recently. Although the intial skin biopsies were negative for amyloidosis, subsequent biopsy established the association of MEN 2A with amyloidosis in this family also. When these kindreds are combined, several conclusions can be drawn. First, the syndrome of cutaneous amyloidosis and MEN 2 A appears to be a clearly defined autosomal dominant hereditary syndrome. Whether this syndrome can be linked to chromosome 10 is not yet known. Second, the dermal amyloid appears to be caused by deposition of keratin-like peptides rather than calcitonin-like peptides. Third, we believe that patients with the hereditary form of cutaneous amyloid should be screened for medullary thyroid carcinoma to determine the true frequency of this syndrome