Bisretinoid-mediated Complement Activation on Retinal Pigment Epithelial Cells Is Dependent on Complement Factor H Haplotype

102

Stargardt disease, an ATP-binding cassette, subfamily A, member 4 (ABCA4)-related retinopathy, is a genetic condition characterized by the accelerated accumulation of lipofuscin in the retinal pigment epithelium, degeneration of the neuroretina, and loss of vision. No approved treatment exists. Here, using a murine model of Stargardt disease, we show that the propensity of vitamin A to dimerize is responsible for triggering the formation of the majority of lipofuscin and transcriptional dysregulation of genes associated with inflammation. Data further demonstrate that replacing vitamin A with vitamin A deuterated at the carbon 20 position (C20-D 3 -vitamin A) impedes the dimerization rate of vitamin A-by approximately fivefold for the vitamin A dimer A2E-and subsequent lipofuscinogenesis and normalizes the aberrant transcription of complement genes without impairing retinal function. Phenotypic rescue by C20-D 3 -vitamin A was also observed noninvasively by quantitative autofluorescence, an imaging technique used clinically, in as little as 3 months after the initiation of treatment, whereas upon interruption of treatment, the age-related increase in autofluorescence resumed. Data suggest that C20-D 3 -vitamin A is a clinically amiable tool to inhibit vitamin A dimerization, which can be used to determine whether slowing the dimerization of vitamin A can prevent vision loss caused by Stargardt disease and other retinopathies associated with the accumulation of lipofuscin in the retina.S targardt disease, first described in 1909, is an autosomal recessive macular dystrophy affecting ∼1 in 10,000 people. The majority of people affected by the disease present with uncorrectable, decreased visual acuity during their teenage years, which most often progresses to legal blindness. To date, there is no approved intervention. Stargardt disease is marked by premature accumulation of lipofuscin in the retinal pigment epithelium (RPE), degeneration of the neuroretina, and subsequent loss of vision. The condition results from mutations in the ATPbinding cassette, subfamily A, member 4 (ABCA4) gene (1), which encodes a transmembrane flippase localized in photoreceptor outer segments. The flippase transports the phosphatidyl-ethanolamineretinaldehyde Schiff base between the cytosol and the cytoplasmic disk surfaces (2). Mutations in ABCA4 also result in retinitis pigmentosa and cone-rod dystrophy and have been linked to age-related macular degeneration (AMD) (3, 4).The accumulation of lipofuscin in the RPE is a common denominator in retinopathies associated with mutations in the ABCA4 gene. Also known as "wear and tear pigment," lipofuscin accumulates as a byproduct of cumulative damage during aging. The brown-yellow, autofluorescent, electron-dense material is also found in cells of the liver, kidney, heart muscle, adrenals, nerve, and ganglion and is considered one of the most consistent morphologic features of aging with a rate of accumulation inversely related to longevity (5, 6). In Stargardt disease, changes in RPE lipof...

Section: Discussionsupporting

confidence: 51%

Rescue of the Stargardt phenotype in Abca4 knockout mice through inhibition of vitamin A dimerization

Issa

Barnard

Herrmann

et al. 2015

102

“…CFH is a soluble CRP secreted by liver and RPE cells (33). Notably, complement activation in bisretinoid-laden RPE cells has been shown to be strongly dependent on the CFH haplotype (34). Moreover, a subset of AMD has been linked to ABCA4 mutations, suggesting a…”

mentioning

confidence: 99%

Complement modulation in the retinal pigment epithelium rescues photoreceptor degeneration in a mouse model of Stargardt disease

Lenis

Sarfare

Jiang

et al. 2017

Self Cite

Recessive Stargardt macular degeneration (STGD1) is caused by mutations in the gene for the ABCA4 transporter in photoreceptor outer segments. STGD1 patients and Abca4−/− (STGD1) mice exhibit buildup of bisretinoid-containing lipofuscin pigments in the retinal pigment epithelium (RPE), increased oxidative stress, augmented complement activation and slow degeneration of photoreceptors. A reduction in complement negative regulatory proteins (CRPs), possibly owing to bisretinoid accumulation, may be responsible for the increased complement activation seen on the RPE of STGD1 mice. CRPs prevent attack on host cells by the complement system, and complement receptor 1-like protein y (CRRY) is an important CRP in mice. Here we attempted to rescue the phenotype in STGD1 mice by increasing expression of CRRY in the RPE using a gene therapy approach. We injected recombinant adeno-associated virus containing the CRRY coding sequence (AAV-CRRY) into the subretinal space of 4-wk-old Abca4 −/− mice. This resulted in sustained, several-fold increased expression of CRRY in the RPE, which significantly reduced the complement factors C3/C3b in the RPE. Unexpectedly, AAV-CRRYtreated STGD1 mice also showed reduced accumulation of bisretinoids compared with sham-injected STGD1 control mice. Furthermore, we observed slower photoreceptor degeneration and increased visual chromophore in 1-y-old AAV-CRRY-treated STGD1 mice. Rescue of the STGD1 phenotype by AAV-CRRY gene therapy suggests that complement attack on the RPE is an important etiologic factor in STGD1. Modulation of the complement system by locally increasing CRP expression using targeted gene therapy represents a potential treatment strategy for STGD1 and other retinopathies associated with complement dysregulation.recessive Stargardt macular degeneration | complement system | retinal pigment epithelium | bisretinoids | gene therapy R ecessive Stargardt macular degeneration (STGD1) is a blinding disease of children and young adults caused by mutations in the ATP binding cassette subfamily A member 4 (ABCA4) gene (1, 2). The pathological hallmark of STGD1 is deposition of autofluorescent lipofuscin in the retinal pigment epithelium (RPE), which precedes photoreceptor degeneration (3, 4). The exact mechanism of how RPE lipofuscin accumulation disrupts overall RPE performance is poorly understood. The RPE fulfills several photoreceptor support tasks, including phagocytosis of distal outer segments (OS) and processing of visual retinoids (5-8). In addition, the RPE plays a major role in controlling the ocular immune response through expression of various complement negative regulatory proteins (CRPs) (9). For these reasons, photoreceptors are critically dependent on a healthy RPE for continued viability.The ABCA4 transporter clears retinaldehyde released by photobleached rhodopsin and cone-opsins from OS discs in the form of N-retinylidene phosphatidylethanolamine (N-ret-PE) (10). As a result, mice lacking ABCA4 accumulate retinaldehyde and N-ret-PE in their OS after light exposu...

“…In fact, recent studies using both mouse- (13) and porcine-derived (14) RPE have demonstrated that RPE cells in culture are capable of forming basal deposits in a cell-autonomous fashion. Furthermore, human fetal RPE (hfRPE) cultures, when exposed to exogenous stressors such as serum (15) or POS (16), have been shown to develop drusen-like basal deposits. However, the ability of cultured human RPE obtained from a macular degeneration patient, in the absence of any exogenous stressors, to develop drusen, has not been investigated.…”

mentioning

confidence: 99%

Drusen in patient-derived hiPSC-RPE models of macular dystrophies

Galloway

Dalvi

Hung

et al. 2017

122

Age-related macular degeneration (AMD) and related macular dystrophies (MDs) are a major cause of vision loss. However, the mechanisms underlying their progression remain ill-defined. This is partly due to the lack of disease models recapitulating the human pathology. Furthermore, in vivo studies have yielded limited understanding of the role of specific cell types in the eye vs. systemic influences (e.g., serum) on the disease pathology. Here, we use human induced pluripotent stem cell-retinal pigment epithelium (hiPSC-RPE) derived from patients with three dominant MDs, Sorsby's fundus dystrophy (SFD), Doyne honeycomb retinal dystrophy/malattia Leventinese (DHRD), and autosomal dominant radial drusen (ADRD), and demonstrate that dysfunction of RPE cells alone is sufficient for the initiation of sub-RPE lipoproteinaceous deposit (drusen) formation and extracellular matrix (ECM) alteration in these diseases. Consistent with clinical studies, sub-RPE basal deposits were present beneath both control (unaffected) and patient hiPSC-RPE cells. Importantly basal deposits in patient hiPSC-RPE cultures were more abundant and displayed a lipid-and protein-rich "drusen-like" composition. Furthermore, increased accumulation of COL4 was observed in ECM isolated from control vs. patient hiPSC-RPE cultures. Interestingly, RPE-specific up-regulation in the expression of several complement genes was also seen in patient hiPSC-RPE cultures of all three MDs (SFD, DHRD, and ADRD). Finally, although serum exposure was not necessary for drusen formation, COL4 accumulation in ECM, and complement pathway gene alteration, it impacted the composition of drusen-like deposits in patient hiPSC-RPE cultures. Together, the drusen model(s) of MDs described here provide fundamental insights into the unique biology of maculopathies affecting the RPE-ECM interface.human induced pluripotent stem cells | retinal pigment epithelium | macular dystrophies | drusen | sub-RPE deposits M aculopathies are a major cause of blindness, with agerelated macular degeneration (AMD) being the leading cause of irreversible vision loss in adults in the United States. Histopathological and clinical studies have shown that AMD and a subset of inherited macular dystrophies (MDs) share extensive phenotypic and clinical similarities (1-4). Specifically, AMD and related MDs have a cumulative etiology with adult onset of signs and symptoms and similar disease presentation including drusen formation, extracellular matrix (ECM) protein accumulation, thickening of Bruch's membrane, development of choroidal neovascularization, retinal pigment epithelium (RPE) atrophy, and ultimately the loss of vision (1-5). Although, the major pathological manifestations in these maculopathies are localized to the RPE-ECM interface in the retina, the multifactorial nature of these diseases, including the involvement of multiple retinal cell layers (photoreceptors, RPE, and choriocapillaris) (3, 6-9) and environmental risk factors (e.g., cigarette smoke) (10), has complicated the pursuit of t...