Abstract
Purpose :
Macrophages are the most abundant and functionally diverse peripheral immune cell type. Their developmental lineage, generally of dual origin, plays an important role in macrophage phenotype and functionality. Tissue “resident” macrophages are derived prenatally and are long-lived, whereas monocyte derived macrophages are adult bone marrow derived and are short-lived. We previously showed macrophages of both origins are abundant in the conventional outflow tract, but their localization and function are unknown. In this study, we determined the distribution of outflow tract macrophages, and a possible role in conventional outflow physiology.
Methods :
Using Cx3cr1-YFPCreER/+ mice with various Cre reporters, long-lived macrophages were conditionally labeled by tamoxifen pulse administration and subsequent wash out. Long-lived macrophages were depleted by targeting Cre driven iDTR. Intraocular pressure (IOP) was measured by iCare tonometry and outflow facility was measured using the iPerfusion system. Anterior segment whole mounts were fixed and labeled with antibodies against CD31 and aSMA, and macrophages were identified as YFP+ (Cx3cr1+) cells by confocal microscopy. Macrophages were counted over 5 non-consecutive anterior segment whole mount images (40X magnification) from n=3 mice/condition. Student’s t test with p < 0.05 was considered significant.
Results :
With long-lived macrophage depletion, there was a 51% reduction in in the trabecular meshwork (TM), whereas no significant depletion was observed in the Schlemm’s canal or distal vessels. In the depletion setting, there was a significant difference in IOP and a corresponding change in outflow facility with long-lived macrophage depletion.
Conclusions :
In the conventional outflow tract, though macrophages of both origins are abundant, long-lived macrophages were enriched in the TM. Moreover, long-lived macrophage depletion resulted in alterations in both IOP and facility, suggesting that TM resident macrophages play a significant role in conventional outflow homeostasis. Future studies elucidating this homeostatic mechanism may help identify new therapeutic targets for glaucoma.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.