Abstract
Purpose :
Stargardt disease type 1 (STGD1) is the most prevalent single-gene retinal dystrophy in humans currently without approved therapies. The ABCA4 gene (expressing the ATP-binding cassette, subfamily A, member number 4 transporter) is responsible for this retinopathy; over 1000 mutations are associated with STGD1. The pathology involves the foveal regions of the macula, progressing outward to the peripheral retina. As abnormal accumulation of cytotoxic N-retinylidene-N-retinylethanolamine (A2E) in the RPE has been linked to the pathology of STGD1, we evaluated whether lowering circulating levels of RBP4 via RNAi-knockdown of transthyretin (TTR) in liver would decrease the amount of A2E in the eyes of Abca4-/-Rdh8-/- mice. Knockdown of TTR lowers circulating levels of both TTR and RBP4, due to increased renal clearance of RBP4 in the absence of TTR.
Methods :
All animal procedures were approved by Animal Care Committees at the University of California, Irvine, and conformed to recommendations of the American Veterinary Medical Association Panel on Euthanasia, and ARVO. We used Abca4-/-Rdh8-/- mice, licensed from Case Western Reserve University. The RNAi targeting mouse-liver TTR was delivered via subcutaneous injection (3 mg/kg, each 21 days). We performed two-photon-excited fluorescence measurements with a Leica TCS SP8 microscope to quantify intraocular condensation products of all-trans-retinal. Quantification of A2E in each whole eye was done separately, using a Vanquish HPLC system coupled with a ThermoFisher Q Exactive mass spectrometer. Changes in retinal histology (anatomical landmarks) were assessed by paraffin-embedding, then sectioning, and H&E staining.
Results :
After treatment with TTR-targeted RNAi, circulating RBP4 levels were decreased in both male and female mice, and both displayed significantly diminished levels of intraocular A2E; two-photon microscopy showed overall condensation products of all-trans-retinal were also decreased. No deleterious impact on retinal structure or function was detected for the RNAi-treated mice compared to vehicle-treated animals.
Conclusions :
Lowering circulating RBP4 levels, via treatment with TTR RNAi, could be a valuable approach for inhibiting accumulation of toxic retinoid derivatives in the eye. This treatment had no negative impact on the eye structures or function, while it diminished A2E content.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.