Abstract
Purpose :
LORD is an autosomal dominant, late onset macular degeneration with marked similarities to AMD. Studies on mouse models of LORD which carry the S163R mutation in C1qtnf5/Ctrp5 led to the proposal that the pathology was mediated through HTRA1 (Chekuri et al, 2019). The purpose of this study was to further elucidate the mechanisms underlying LORD.
Methods :
Choroid proteomes were determined for 5m and 18m C57BL/6J Wt mice, mice with the S163R mutation in C1qtnf5/Ctrp5 (Ctrp5+/-) and mice with the gene knocked out (Ctrp5-/-). Tryptic peptide masses were determined on a ThermoFisher Q-Exactive mass spectrometer. Peptide and protein identification and label free quantification were done using MaxQuant software. Aging was defined by the 18m/5m ratios of LFQ intensities.
Results :
CTRP5 was increased 9.9 fold in Ctrp5+/- mice over Wt mice at 5m. Wt CTRP5 and S163R-CTRP5 were present in Ctrp5+/- mice at about equal levels. Both forms interact with HTRA1, but only Wt CTRP5 was cleaved by HTRA1 (Chekuri et al 2019). The mutation also led to a 5.3 fold increase in HTRA1 in Ctrp5+/- mice at 5m, however, significant reductions in HTRA1 substrates including TGFB1, LTBP1, LTBP4 and many ECM proteins were not observed at 5m in Ctrp5+/- mice. These results suggest HTRA1 activity was not significantly increased in Ctrp5+/- at 5m. By 18m HTRA1 substrates were all altered essentially to the same extent and in the same direction in Wt and Ctrp5+/- mice. TGFB1 signaling was negatively attenuated similarly in both Wt and Ctrp5+/- mice, independent of the increased level of HTRA1 in 5m Ctrp5+/- mice, by decreased levels of TGFB1 and increased levels of CD109 and NEDD4.
A significant mast cell response specific to Ctrp5+/- mice also began about 5m. By 18m the mast cell specific proteases (CMA1, MCPT4, TPSB2, CPA3) were increased 10-13 fold in Ctrp5+/- mice. This suggested that CTRP5 hetero-oligomers (Wt and mutant CTRP5) in Ctrp5+/-, but not homo-oligomers of mutant CTRP5 or the absence of CTRP5 elicited the strong mast cell response. LGALS3 and IBA1, markers of inflammation, were significantly elevated in Ctrp5+/- mice compared to Wt mice.
Conclusions :
The pathobiology in mouse models of LORD was mediated through an inflammatory response to the accumulation of aggregates of HTRA1 with CTRP5 hetero-oligomers which diminished HTRA1 activity.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.