Proteomic insight into the pathogenesis of CAPN5-vitreoretinopathy

Abstract

CAPN5 Neovascular Inflammatory Vitreoretinopathy (CAPN5-NIV; OMIM 193235) is a poorly-understood rare, progressive inflammatory intraocular disease with limited therapeutic options. To profile disease effector proteins in CAPN5-NIV patient vitreous, liquid vitreous biopsies were collected from two groups: eyes from control subjects (n = 4) with idiopathic macular holes (IMH) and eyes from test subjects (n = 12) with different stages of CAPN5-NIV. Samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Protein expression changes were evaluated by principal component analysis, 1-way ANOVA (significant p-value < 0.05), hierarchical clustering, gene ontology, and pathway representation. There were 216 differentially-expressed proteins (between CAPN5-NIV and control vitreous), including those unique to and abundant in each clinical stage. Gene ontology analysis revealed decreased synaptic signaling proteins in CAPN5-NIV vitreous compared to controls. Pathway analysis revealed that inflammatory mediators of the acute phase response and the complement cascade were highly-represented. The CAPN5-NIV vitreous proteome displayed characteristic enrichment of proteins and pathways previously-associated with non-infectious posterior uveitis, rhegmatogenous retinal detachment (RRD), age-related macular degeneration (AMD), proliferative diabetic retinopathy (PDR), and proliferative vitreoretinopathy (PVR). This study expands our knowledge of affected molecular pathways in CAPN5-NIV using unbiased, shotgun proteomic analysis rather than targeted detection platforms. The high-levels and representation of acute phase response proteins suggests a functional role for the innate immune system in CAPN5-NIV pathogenesis.

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“…Changes in the local immune microenvironment and FasL expression may in fact lead to FasL-mediated activation of the innate immune system and termination of ocular immune privilege ( Gregory et al., 2002 ). Indeed, innate immune effectors (e.g., acute phase response proteins and complement) have been previously implicated in NIV and uveitis pathogenesis ( Rosenbaum and Kim, 2013 ; Velez et al., 2019 ).…”

“…As different proteomic platforms can give different results, we obtained a more global view of the NIV vitreous proteome using liquid chromatography-tandem mass spectrometry (LC-MS/MS) ( Velez et al., 2019 ). We also compared our previously published MS-based analysis of Stage II NIV vitreous to proteomes from other etiologies of intraocular inflammation such as autoimmune retinopathy, idiopathic posterior uveitis, and lens-induced uveitis (LIU; unpublished data; Figure 4 A).…”

“…The loss of the ERG b-wave in patients with Stage I NIV indicates the presence of early synaptic signaling defects, akin to retinitis pigmentosa (RP) ( Tang et al, 2018 ). LC-MS/MS analysis revealed that synaptic signaling proteins (e.g., neurexin-2, glutamate receptor 4, neurofascin, neuronal growth regulator 1, and oligodendrocyte-myelin glycoprotein) were depleted in NIV vitreous compared with non-inflammatory controls ( Velez et al., 2019 ). It is possible that the loss of the identified synaptic signaling proteins contributes to the early ERG defect that is characteristic of NIV ( Velez et al., 2019 ; Wert et al., 2020 ).…”

“…LC-MS/MS analysis revealed that synaptic signaling proteins (e.g., neurexin-2, glutamate receptor 4, neurofascin, neuronal growth regulator 1, and oligodendrocyte-myelin glycoprotein) were depleted in NIV vitreous compared with non-inflammatory controls ( Velez et al., 2019 ). It is possible that the loss of the identified synaptic signaling proteins contributes to the early ERG defect that is characteristic of NIV ( Velez et al., 2019 ; Wert et al., 2020 ). Whether CAPN5 directly targets these proteins in the retina (or their upstream effectors) is still not known.…”

“…As different proteomic platforms can give different results, we obtained a more global view of the NIV vitreous proteome using liquid chromatography-tandem mass spectrometry (LC-MS/MS) (Velez et al, 2019).…”