CTRP5 is a membrane-associated and secretory protein in the RPE and ciliary body and the S163R mutation of CTRP5 impairs its secretion.
OBJECTIVE
In a prior study, a S163R mutation in the complement-1q tumor necrosis factor-related protein 5 (CTRP5/ C1QTNF5) was reported to be associated with early-onset long anterior zonules (LAZ) and late-onset retinal degeneration (L-ORD). The ocular tissues involved in the phenotype are the retinal pigment epithelium (RPE) in the posterior segment and ciliary epithelium (CE) and lens in the anterior segment. The purpose of this study was to characterize the spatial and temporal expression of the mouse Ctrp5 gene, determine tissue and subcellular localization, and study the effect of the S163R mutation.


METHODS
The expression of the Ctrp5 gene in the mouse was studied by quantitative (q)RT-PCR and in situ hybridization. CTRP5 protein expression and distribution were studied by Western blot analysis, immunohistochemistry, and immunoelectron microscopy. Cellular location of wild-type and mutant CTRP5 in MDCK and COS-7 cells was determined by immunofluorescence and immunoblot analysis.


RESULTS
A significant level of Ctrp5 expression was detected in the adult mouse in the ciliary body (CB) and RPE, and expression started at a very early stage of embryogenesis. Immunohistochemical analysis showed CTRP5 protein in the apical processes of the RPE and forming a hexagonal lattice associated with the RPE lateral membranes. In the ciliary body, CTRP5 was localized to the apical aspects of the CE, the region between the bilayered ciliary epithelial cells. The membrane association of CTRP5 in the RPE and CE was further confirmed by immunoelectron microscopy. Furthermore, cultured cells were used to show that the CTRP5 is a secretory protein and that its secretion is impaired by the S163R mutation.


CONCLUSIONS
CTRP5, a secretory and membrane-associated protein, is localized to the lateral and apical membranes of the RPE and CB. Impaired secretion of the mutant protein may underlie the pathophysiology of L-ORD and LAZ.
Mandal
Md Nawajes A
MN
Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA.
Vasireddy
Vidyullatha
V
Reddy
G Bhanuprakash
GB
Wang
Xiaofei
X
Moroi
Sayoko E
SE
Pattnaik
Bikash R
BR
Hughes
Bret A
BA
Heckenlively
John R
JR
Hitchcock
Peter F
PF
Jablonski
Monica M
MM
Ayyagari
Radha
R
D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002522:Chlorocebus aethiops; D002924:Ciliary Body / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression / Q000502:physiology; D017403:In Situ Hybridization; D007905:Lens Diseases / Q000235:genetics; D008022:Ligaments / Q000002:abnormalities; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D016253:Microscopy, Immunoelectron; D016297:Mutagenesis, Site-Directed; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D017354:Point Mutation; D012162:Retinal Degeneration / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
C516596:CTRP5 protein, mouse; D008565:Membrane Proteins