calpain and Uveitis

CAPN5 mutations have been linked to autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV), a blinding autoimmune eye disease. Here, we link a new CAPN5 mutation to ADNIV and model the three-dimensional structure of the resulting mutant protein. In our study, a kindred with inflammatory vitreoretinopathy was evaluated by clinical eye examinations, DNA sequencing, and protein structural modeling to investigate the disease-causing mutation. Two daughters of an affected mother demonstrated symptoms of stage III ADNIV, with posterior uveitis, cystoid macular edema, intraocular fibrosis, retinal neovascularization, retinal degeneration, and cataract. The women also harbored a novel guanine to thymine (c.750G>T, p.Lys250Asn) missense mutation in exon 6 of CAPN5, a gene that encodes a calcium-activated cysteine protease, calpain-5. Modeling based on the structures of all known calpains revealed the mutation falls within a calcium-sensitive flexible gating loop that controls access to the catalytic groove. Three-dimensional modeling placed the new mutation in a region adjacent to two previously identified disease-causing mutations, all three of which likely disrupt hydrogen bonding within the gating loop, yielding a CAPN5 with altered enzymatic activity. This is the third case of a CAPN5 mutation leading to inherited uveitis and neovascular vitreoretinopathy, suggesting patients with ADNIV features should be tested for CAPN5 mutations. Structural modeling of novel variants can be used to support mechanistic consequences of the disease-causing variants.

Topics: Base Sequence; Calpain; Computational Biology; DNA Primers; Female; Fluorescein Angiography; Humans; Models, Molecular; Molecular Sequence Data; Mutation, Missense; Pedigree; Phenotype; Protein Conformation; Retinal Detachment; Sequence Analysis, DNA; Tomography, Optical Coherence; Uveitis; Vitreoretinopathy, Proliferative

A single amino acid mutation near the active site of the CAPN5 protease was linked to the inherited blinding disorder, autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV, OMIM #193235). In homology modeling with other calpains, this R243L CAPN5 mutation was situated in a mobile loop that gates substrate access to the calcium-regulated active site. In in vitro activity assays, the mutation increased calpain protease activity and made it far more active at low concentrations of calcium. To test whether the disease allele could yield an animal model of ADNIV, we created transgenic mice expressing human (h) CAPN5(R243L) only in the retina. The resulting hCAPN5(R243L) transgenic mice developed a phenotype consistent with human uveitis and ADNIV, at the clinical, histological and molecular levels. The fundus of hCAPN5(R243L) mice showed enhanced autofluorescence (AF) and pigment changes indicative of reactive retinal pigment epithelial cells and photoreceptor degeneration. Electroretinography showed mutant mouse eyes had a selective loss of the b-wave indicating an inner-retina signaling defect. Histological analysis of mutant mouse eyes showed protein extravasation from dilated vessels into the anterior chamber and vitreous, vitreous inflammation, vitreous and retinal fibrosis and retinal degeneration. Analysis of gene expression changes in the hCAPN5(R243L) mouse retina showed upregulation of several markers, including members of the Toll-like receptor pathway, chemokines and cytokines, indicative of both an innate and adaptive immune response. Since many forms of uveitis share phenotypic characteristics of ADNIV, this mouse offers a model with therapeutic testing utility for ADNIV and uveitis patients.

Topics: Animals; Calpain; Cell Line; Genetic Diseases, Inborn; Humans; Inflammation; Mice; Mice, Transgenic; Uveitis

Samples of the vitreous were analysed in order to identify changes of soluble proteins in vitreo-retinal disease. The soluble proteins of the vitreous were separated on an anion exchange column (Mono-Q). The degree of neutral proteolytic activity in vitreous body was also measured. The vitreous from cataract cases without vitreoretinal disease was characterized by its low content of soluble proteins equivalent to about 1% of that of serum. Albumin and transferrin were the major identified components and their concentrations were approximately 0.85 and 0.03 g/l, respectively. In cases with vitreoretinal disease the vitreous showed changes of total soluble protein and the appearance of additional protein peaks. In patients with PVR the albumin concentration in the vitreous was found to be three times higher as compared to the control group consisting of patients with cataract. Neutral proteolytic activity in the vitreous was relatively low in both normal and pathological vitreous.

Topics: Aged; Albumins; Calpain; Cataract; Chromatography, High Pressure Liquid; Eye Diseases; Eye Proteins; Humans; Middle Aged; Retinal Diseases; Solubility; Transferrin; Uveitis; Vitrectomy; Vitreous Body