Macrophages are essential for CTGF-mediated adult ß-cell proliferation after injury.

OBJECTIVE: Promotion of endogenous ß-cell mass expansion could facilitate regeneration in patients with diabetes. We discovered that the secreted protein CTGF (aka CCN2) promotes adult ß-cell replication and mass regeneration after injury via increasing ß-cell immaturity and shortening the replicative refractory period. However, the mechanism of CTGF-mediated ß-cell proliferation is unknown. Here we focused on whether CTGF alters cells of the immune system to enhance ß-cell replication. METHODS: Using mouse models for 50% ß-cell ablation and conditional, ß-cell-specific CTGF induction, we assessed changes in immune cell populations by performing immunolabeling and gene expression analyses. We tested the requirement for macrophages in CTGF-mediated ß-cell proliferation via clodronate-based macrophage depletion. RESULTS: CTGF induction after 50% ß-cell ablation increased both macrophages and T-cells in islets. An upregulation in the expression of several macrophage and T-cell chemoattractant genes was also observed in islets. Gene expression analyses suggest an increase in M1 and a decrease in M2 macrophage markers. Depletion of macrophages (without changes in T cell number) blocked CTGF-mediated ß-cell proliferation and prevented the increase in ß-cell immaturity. CONCLUSIONS: Our data show that macrophages are critical for CTGF-mediated adult ß-cell proliferation in the setting of partial ß-cell ablation. This is the first study to link a specific ß-cell proliferative factor with immune-mediated ß-cell proliferation in a ß-cell injury model.

Connective tissue growth factor modulates adult ß-cell maturity and proliferation to promote ß-cell regeneration in mice.

Stimulation of endogenous ß-cell expansion could facilitate regeneration in patients with diabetes. In mice, connective tissue growth factor (CTGF) is expressed in embryonic ß-cells and in adult ß-cells during periods of expansion. We discovered that in embryos CTGF is necessary for ß-cell proliferation, and increased CTGF in ß-cells promotes proliferation of immature (MafA(-)) insulin-positive cells. CTGF overexpression, under nonstimulatory conditions, does not increase adult ß-cell proliferation. In this study, we tested the ability of CTGF to promote ß-cell proliferation and regeneration after partial ß-cell destruction. ß-Cell mass reaches 50% recovery after 4 weeks of CTGF treatment, primarily via increased ß-cell proliferation, which is enhanced as early as 2 days of treatment. CTGF treatment increases the number of immature ß-cells but promotes proliferation of both mature and immature ß-cells. A shortened ß-cell replication refractory period is also observed. CTGF treatment upregulates positive cell-cycle regulators and factors involved in ß-cell proliferation, including hepatocyte growth factor, serotonin synthesis, and integrin ß1. Ex vivo treatment of whole islets with recombinant human CTGF induces ß-cell replication and gene expression changes consistent with those observed in vivo, demonstrating that CTGF acts directly on islets to promote ß-cell replication. Thus, CTGF can induce replication of adult mouse ß-cells given a permissive microenvironment.