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

Riley KG, Pasek RC, Maulis MF, Dunn JC, Bolus WR, Kendall PL, Hasty AH, Gannon M
Mol Metab. 2015 4 (8): 584-91

PMID: 26266091 · PMCID: PMC4529497 · DOI:10.1016/j.molmet.2015.05.002

OBJECTIVE - Promotion of endogenous β-cell mass expansion could facilitate regeneration in patients with diabetes. We discovered that the secreted protein CTGF (aka CCN2) promotes adult β-cell replication and mass regeneration after injury via increasing β-cell immaturity and shortening the replicative refractory period. However, the mechanism of CTGF-mediated β-cell proliferation is unknown. Here we focused on whether CTGF alters cells of the immune system to enhance β-cell replication.

METHODS - Using mouse models for 50% β-cell ablation and conditional, β-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 β-cell proliferation via clodronate-based macrophage depletion.

RESULTS - CTGF induction after 50% β-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 β-cell proliferation and prevented the increase in β-cell immaturity.

CONCLUSIONS - Our data show that macrophages are critical for CTGF-mediated adult β-cell proliferation in the setting of partial β-cell ablation. This is the first study to link a specific β-cell proliferative factor with immune-mediated β-cell proliferation in a β-cell injury model.

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