Macrophage dynamics are regulated by local macrophage proliferation and monocyte recruitment in injured pancreas

Area of Science:

• Immunology
• Endocrinology
• Regenerative Medicine

Background:

• Partial duct ligation (PDL) in the pancreas initiates a healing response involving beta-cell neogenesis and proliferation.
• Macrophages (MΦs) are implicated in promoting beta-cell proliferation post-PDL, but their specific roles and diversity remain unclear.

Purpose of the Study:

• To comprehensively characterize myeloid cell diversity and dynamics in the pancreas following acute injury induced by PDL.
• To elucidate the factors governing macrophage recruitment and proliferation after PDL.
• To determine the functional contribution of distinct macrophage subsets to pancreas repair and beta-cell regeneration.

Main Methods:

• Flow cytometry and molecular profiling to identify and differentiate pancreas macrophage subsets (MHC-II(lo) and MHC-II(hi)).
• Induction of PDL in mice to model acute pancreas injury.
• Analysis of myeloid cell infiltration and proliferation using genetic models (e.g., C-C chemokine receptor 2-KO mice).
• Assessment of macrophage functional properties, including angiogenic potential and contribution to beta-cell proliferation.

Main Results:

• Naive pancreas contains two main tissue-resident macrophage populations: MHC-II(lo) (more M2-activated, angiogenic) and MHC-II(hi) (predominant).
• PDL induces early Ly6C(hi) monocyte infiltration, followed by a transient MHC-II(lo) macrophage peak, and eventual restoration of MHC-II(hi) dominance.
• Macrophage dynamics are regulated by C-C chemokine receptor 2 and macrophage-colony stimulating factor receptor signaling, influencing both recruitment and local proliferation.
• Tissue-resident macrophages, particularly MHC-II(lo) types, are crucial for beta-cell proliferation post-PDL, especially in the absence of significant monocyte infiltration.

Conclusions:

• This study provides a detailed characterization of pancreas macrophage subsets and their dynamic behavior following injury.
• Distinct macrophage populations play specific roles in pancreas repair, with tissue-resident MΦs being key drivers of beta-cell proliferation.
• Understanding these macrophage dynamics offers insights into therapeutic strategies for pancreas regeneration.