Abstract
Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss. The protein HtrA1 is enriched in retinal pigment epithelial (RPE) cells isolated from AMD patients and in drusen deposits. However, it is poorly understood how increased levels of HtrA1 affect the physiological function of the RPE at the intracellular level. Here, we developed hfRPE (human fetal retinal pigment epithelial) cell culture model where cells fully differentiated into a polarized functional monolayer. In this model, we fine-tuned the cellular levels of HtrA1 by targeted overexpression. Our data show that HtrA1 enzymatic activity leads to intracellular degradation of tubulin with a corresponding reduction in the number of microtubules, and consequently to an altered mechanical cell phenotype. HtrA1 overexpression further leads to impaired apical processes and decreased phagocytosis, an essential function for photoreceptor survival. These cellular alterations correlate with the AMD phenotype and thus highlight HtrA1 as an intracellular target for therapeutic interventions towards AMD treatment.
Highlights
Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in the elderly population (Coleman et al, 2008)
HtrA1 was shown to play an important physiological role in extracellular matrix homeostasis and to cleave a substantial number of its components, such as fibronectin, type III collagen, decorin, aggrecan and intracellular proteins such as tubulin (Canfield et al, 2007; Chien et al, 2004; De Luca et al, 2003; Schmidt et al, 2016).The HtrA1 protein has been reported to be present in drusen deposits, a hallmark of AMD pathogenesis, and within retinal pigment epithelial (RPE) cells isolated from AMD patients, albeit in a small cohort of patients (Tuo et al, 2008)
We show clinical data from 10 post-mortem retinas extracted from 5 AMD patients and 5 healthy subjects that suggest an overexpression of HtrA1 in AMD and an overexpression in the RPE layer of AMD patients
Summary
Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in the elderly population (Coleman et al, 2008). Despite different studies which aimed to define the role of HtrA1 in human RPE at the molecular level (Saini et al, 2017; Supanji et al, 2013), it remains to be further investigated how elevated levels of HtrA1 affect the physiological function of the RPE This is partially due to the dearth of polarized cell culture models that accurately preserve the RPE phenotype and which could serve as a relevant cell model to investigate the consequences of HtrA1 pathological overexpression. We report the translation of this phenotype into impaired phagocytosis activity, a master function of the RPE ensuring photoreceptor survival These findings delineate how induced HtrA1 could be contributing to the etiology of AMD and provide initial mechanistic insight into the intracellular role of HtrA1 in RPE cells
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