Retinal mid-peripheral capillary free zones are enlarged in cognitively unimpaired older adults at high risk for Alzheimer's disease.

BACKGROUND: Compared to standard neuro-diagnostic techniques, retinal biomarkers provide a probable low-cost and non-invasive alternative for early Alzheimer's disease (AD) risk screening. We have previously quantified the periarteriole and perivenule capillary free zones (mid-peripheral CFZs) in cognitively unimpaired (CU) young and older adults as novel metrics of retinal tissue oxygenation. There is a breakdown of the inner retinal blood barrier, pericyte loss, and capillary non-perfusion or dropout in AD leading to potential enlargement of the mid-peripheral CFZs. We hypothesized the mid-peripheral CFZs will be enlarged in CU older adults at high risk for AD compared to low-risk individuals. METHODS: 20 × 20° optical coherence tomography angiography images consisting of 512 b-scans, 512 A-scans per b-scan, 12-µm spacing between b-scans, and 5 frames averaged per each b-scan location of the central fovea and of paired major arterioles and venules with their surrounding capillaries inferior to the fovea of 57 eyes of 37 CU low-risk (mean age: 66 years) and 50 eyes of 38 CU high-risk older adults (mean age: 64 years; p = 0.24) were involved in this study. High-risk participants were defined as having at least one APOE e4 allele and a positive first-degree family history of AD while low-risk participants had neither of the two criteria. All participants had Montreal Cognitive Assessment scores ≥ 26. The mid-peripheral CFZs were computed in MATLAB and compared between the two groups. RESULTS: The periarteriole CFZ of the high-risk group (75.8 ± 9.19 µm) was significantly larger than that of the low-risk group (71.3 ± 7.07 µm), p = 0.005, Cohen's d = 0.55. The perivenule CFZ of the high-risk group (60.4 ± 8.55 µm) was also significantly larger than that of the low-risk group (57.3 ± 6.40 µm), p = 0.034, Cohen's d = 0.42. There were no significant differences in foveal avascular zone (FAZ) size, FAZ effective diameter, and vessel density between the two groups, all p > 0.05. CONCLUSIONS: Our results show larger mid-peripheral CFZs in CU older adults at high risk for AD, with the potential for the periarteriole CFZ to serve as a novel retinal vascular biomarker for early AD risk detection.

Regulation of fibronectin-EDA through CTGF domain-specific interactions with TGFß2 and its receptor TGFßRII.

PURPOSE: To investigate the role of fibronectin containing extra domain A (FN-EDA) in the pathogenesis of proliferative vitreoretinopathy (PVR) and the regulation of FN-EDA by transforming growth factor (TGF)-ß and connective tissue growth factor (CTGF) in retinal pigment epithelial (RPE) cells. METHODS: Expression of FN-EDA in normal human retinas and PVR membranes was evaluated by immunohistochemistry. The effects of TGFß and CTGF on FN-EDA mRNA and protein expression in primary cultures of human RPE cells were analyzed at different time points by real-time PCR and Western blot, respectively. The interaction of CTGF with TGFß2 or with its type II receptor TGFßRII was examined by ELISA, immunoprecipitation, and solid-phase binding assays. RESULTS: FN-EDA was abundantly expressed in PVR membranes but absent from the RPE monolayer in normal human retinas. Treatment of RPE cells with TGFß2 induced FN-EDA expression in a time- and dose-dependent manner, but CTGF alone had no effect. However, CTGF, through its N-terminal half fragment, augmented TGFß2-induced expression of FN-EDA at the protein level. This effect was blocked by antibodies against TGFß2 or TGFßRII. Interaction of TGFß2 or TGFßRII with CTGF was dose dependent and specific. CTGF directly bound TGFß2 and TGFßRII at its N- and C-terminal domains, respectively. CONCLUSIONS: These findings suggest that CTGF promotes the profibrotic activities of TGFß acting as a cofactor through direct protein interactions and complex regulatory mechanisms.

Connective tissue growth factor as a mediator of intraocular fibrosis.

PURPOSE: To investigate the role of connective tissue growth factor (CTGF) in the pathogenesis of proliferative vitreoretinopathy (PVR). METHODS: Expression of CTGF was evaluated immunohistochemically in human PVR membranes, and the accumulation of CTGF in the vitreous was evaluated by ELISA. The effects of CTGF on type I collagen mRNA and protein expression in RPE were assayed by real-time PCR and ELISA, and migration was assayed with a Boyden chamber assay. Experimental PVR was induced in rabbits with vitreous injection of RPE cells plus rhCTGF; injection of RPE cells plus platelet derived-growth factor, with or without rhCTGF, or by injection of RPE cells infected with an adenoviral vector that expressed CTGF. RESULTS: CTGF was highly expressed in human PVR membranes and partially colocalized with cytokeratin-positive RPE cells. Treatment of RPE with rhCTGF stimulated migration with a peak response at 50 ng/mL (P < 0.05) and increased expression of type I collagen (P < 0.05). There was a prominent accumulation of the N-terminal half of CTGF in the vitreous of patients with PVR. Intravitreous injection of rhCTGF alone did not produce PVR, whereas such injections into rabbits with mild, nonfibrotic PVR promoted the development of dense, fibrotic epiretinal membranes. Similarly, intravitreous injection of RPE cells infected with adenoviral vectors that overexpress CTGF induced fibrotic PVR. Experimental PVR was associated with increased CTGF mRNA in PVR membranes and accumulation of CTGF half fragments in the vitreous. CONCLUSIONS: The results identify CTGF as a major mediator of retinal fibrosis and potentially an effective therapeutic target for PVR.