Abstract
Purpose :
Macrophages are present in all tissues of the body but vary in phenotype and functionality based on their developmental origins. Tissue resident macrophages are derived prenatally and are long-lived, whereas monocyte-derived macrophages are adult bone marrow derived and are short-lived. Our previous work has shown that macrophages of both origins are present abundantly in the conventional outflow tract, however long-lived macrophages are enriched in the trabecular meshwork, where they act to regulate intraocular pressure (IOP). The purpose of this study is to determine the distribution and function of short-lived macrophages in IOP homeostasis.
Methods :
CCR2RFP/RFP (KO) mice lack short-lived macrophages in most tissues, as the chemokine receptor is required for monocytes to leave the bone marrow. Using these KO mice (and hemizygous controls), anterior segment whole mounts were fixed and labeled with antibodies against IBA1, CD31 and aSMA. Macrophages were counted over 5 non-consecutive anterior segment whole mount images from 3 mice per condition. IOP was measured by rebound tonometry, and proximal outflow facility (trabecular meshwork and Schlemm’s canal) was measured ex vivo using the iPerfusion system. Statistical analysis was performed by Student’s t test with p<0.05 considered significant.
Results :
Short-lived macrophages were 10-fold more abundant around distal vessels than in trabecular meshwork and Schlemm’s canal. CCR2 KO mice exhibited a reduction in short-lived macrophages in all outflow tissues: around distal vessels, in trabecular meshwork and Schlemm’s canal (p < 0.0001, p < 0.0001 and p < 0.01, respectively). Strikingly, CCR2 KO produced a significant decrease in IOP (19.3±0.3 (SEM) to 16.9±0.2 mmHg, p < 0.001), but there was no change in outflow facility (1.7±0.2 to 1.6±0.2 nl/min/mmHg, p = 0.75).
Conclusions :
CCR2 KO resulted in a decrease in IOP, in contrast to long-lived macrophage depletion that led to an increase in IOP, which supports differential roles of short-lived and long-lived macrophages in IOP homeostasis. Since short-lived macrophages are enriched around distal vessels, we hypothesize that the reduced IOP is due to changes in distal outflow facility, requiring in vivo measurements.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.