The normalizing effects of the CYP46A1 activator efavirenz on retinal sterol levels and risk factors for glaucoma in Apoj−/− mice

Abstract

Apolipoprotein J (APOJ) is a multifunctional protein with genetic evidence suggesting an association between APOJ polymorphisms and Alzheimer’s disease as well as exfoliation glaucoma. Herein we conducted ocular characterizations of Apoj−/− mice and found that their retinal cholesterol levels were decreased and that this genotype had several risk factors for glaucoma: increased intraocular pressure and cup-to-disk ratio and impaired retinal ganglion cell (RGC) function. The latter was not due to RGC degeneration or activation of retinal Muller cells and microglia/macrophages. There was also a decrease in retinal levels of 24-hydroxycholesterol, a suggested neuroprotectant under glaucomatous conditions and a positive allosteric modulator of N-methyl-d-aspartate receptors mediating the light-evoked response of the RGC. Therefore, Apoj−/− mice were treated with low-dose efavirenz, an allosteric activator of CYP46A1 which converts cholesterol into 24-hydroxycholesterol. Efavirenz treatment increased retinal cholesterol and 24-hydroxycholesterol levels, normalized intraocular pressure and cup-to-disk ratio, and rescued in part RGC function. Retinal expression of Abcg1 (a cholesterol efflux transporter), Apoa1 (a constituent of lipoprotein particles), and Scarb1 (a lipoprotein particle receptor) was increased in EVF-treated Apoj−/− mice, indicating increased retinal cholesterol transport on lipoprotein particles. Ocular characterizations of Cyp46a1−/− mice supported the beneficial efavirenz treatment effects via CYP46A1 activation. The data obtained demonstrate an important APOJ role in retinal cholesterol homeostasis and link this apolipoprotein to the glaucoma risk factors and retinal 24-hydroxycholesterol production by CYP46A1. As the CYP46A1 activator efavirenz is an FDA-approved anti-HIV drug, our studies suggest a new therapeutic approach for treatment of glaucomatous conditions.

Proteomic analysis uncovers clusterin-mediated disruption of actin-based contractile machinery in the trabecular meshwork to lower intraocular pressure

“…However, in our previous study, we showed that the levels of a stress response chaperone protein clusterin were decreased under several IOP dysregulators in TM [7] resulting in a loss of clusterin function. Further, we found that functional loss of clusterin produces a significant increase in IOP [7] which was independently validated by another study [8]. Noticeably, our study uncovered that at the cellular level, reduced clusterin triggered significant actin reorganization evidenced by increased levels of actin-associated proteins and membrane proteins like integrins[7].…”

A distributed integral control mechanism for the regulation of cholesterol concentration in the human retina

“…Significantly, a most recent study involving in vivo imaging of the mouse retina to track lipoprotein particles and lipid distribution, provides an explanation of why in situ biosynthesis is the major source of cholesterol for the retina; their data indicates limited trafficking of serum lipoprotein particles (LPP) from the RPE to the neural retina, thus it seems to stimulate de novo synthesis of cholesterol in the neural retina (El-Darzi et al 2024).…”

“…BM consists of five layers; the basal lamina of the RPE, inner collagenous layer (ICL), elastic layer (EL), outer collagenous layer (OCL) and the basal lamina of the choriocapillary endothelium (BL) (Fig 2). Tight junctions between the RPE cells play a crucial role in establishing its apical-to-basolateral polarity and in forming the outer retinal-blood barrier to prevent diffusion of large molecules from the choroid to the retina (Strauss 2005;El-Darzi et al 2024). Starting from the RPE's embryonic origin, coordinated maturation requires the cells to adapt to different functional properties of the retina.…”

Cholesterol and oxysterols in retinal neuron-glia interactions: relevance for glaucoma

“…ABCA1 and ABCG1 were shown to be expressed in all cell layers of the mouse retina using immunofluorescence ( 53 ). At the apical membrane of RPE cells, these transporters enable the delivery of exogenous cholesterol to the neural retina using ApoA-I, ApoE ( 54 ) and ApoJ ( 55 ). The monkey and human neural retinas have been shown to express most of the major proteins involved in lipid transport such as ABCA1, ApoA-I, ApoE, SRB-I, SRB-II, CD36 using immunofluorescence.…”