Abstract
Purpose :
Mast cells are present in essentially all mammalian choroid suggesting an essential biological role. Recent studies identified increased choroid mast cells in early AMD and in the sub-macular regions of individuals with risk alleles of AMD (CFHY402H and at HTRA1/ARMS2 locus). The purpose of this study was to understand the effect of age on mast cells in the choroid of Wt mice and in mouse models of late onset retinal degeneration (L-ORD), a monogenic disorder caused by the S163R mutation in C1QTNF5/CTRP5.
Methods :
The choroid proteomes were determined for Wt mice and 3 mouse models of L-ORD (CTRP5-KI/Wt, CTRP5-KI/KI and CTRP5-KO). Peptides and proteins were identified from the mass spectral data and quantified using MaxQuant software. Aging was defined as quantitative changes (p<.05) between 5 and 18 mo in Wt choroid.
Results :
Four proteases highly specific for mast cells were present in the choroids of Wt mice and the CTRP5 mutant mice confirming the presence of connective tissue type mast cells in the mouse choroid. These proteases were CMA1 (chymase), MCPT4, TPSB2 (tryptase) and CPA3 (carboxypeptidase A3). The level of each protease at 5 mo was comparable irrespective of the genotype. Each protease increased significantly with age. In Wt mice the levels increased 3-3.6 fold. The largest increases with age were in CTRP5-KI/Wt mice (10-13 fold); this reflects the combination of aging and the result of mutation induced changes. Changes were intermediate for CTRP5-KO (3.5-6 fold) and CTRP5-KI/KI (4-7 fold). Proteins with roles in mast cell biology changed 2-5 fold with age in Wt and CTRP5-KI/Wt mice. They included HPSE, CLU, LGALS3, ALOX5AP, FCER1G, CTSS and PTPRC, however, not all of these are restricted to mast cells. LXN, an inhibitor of CPA3, was increased in 18 mo CTRP5-KI/Wt. We previously reported significant increases in CTRP5 and HTRA1 protein in CTRP5 mutant mice. The increase in mast cells did not correlate with concentrations of these proteins or their change with age but correlated with the presence of hetero-oligomers of Wt and mutant CTRP5.
Conclusions :
The increase in mast cells in Wt mice may contribute to increased inflammation and choroidal aging. We propose that a change in the structure and function of CTRP5 in KI/Wt mutant mice caused the further increase in mast cells. These results support the hypothesis that mast cells contribute to the pathobiology of macular degenerations.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.