CAPN5 genetic inactivation phenotype supports therapeutic inhibition trials

Treatment and Visual Outcomes in Pediatric Patients with Autosomal Dominant Neovascular Inflammatory Vitreoretinopathy: A Cohort Study

BACKGROUND

Autosomal dominant neovascular inflammatory vitreoretinopathy (NIV), formerly called "ADNIV," is a rare autoinflammatory condition mainly of adulthood caused by mutations in calcium-activated calpain-5 protease (CAPN5). Our aim is to report the treatment and visual outcomes of children newly diagnosed with NIV after systemic treatment.

METHODS

We reviewed charts of patients ≤18 years old with CAPN5 gene mutation, ocular findings consistent with NIV, and treated with systemic immunosuppression for a minimum of 6 months. Treatment response was based on ophthalmic examination, ultra-widefield fluorescein-angiography (UWFFA), and optical coherence tomography (OCT).

RESULTS

Eight children (16 eyes) were diagnosed with NIV at a median age of 14 (Range [R] 9-16) years, with a median follow-up of 18 months (R6-20). At diagnosis, one patient had impaired visual acuity (VA > 0.4), eight had vascular leakage, two had neovascularization, and three had macular edema. All responded to oral or local glucocorticoids but was not sustained. Systemic immunosuppression was started in seven patients with methotrexate and infliximab after a median time from diagnosis of 1.5 months (R0.5-2) and 3.2 months (R2.5-3.1), respectively. Infliximab was discontinued in all after a median time of 7 months (R3.5-10) for ineffectiveness, and 5/7 switched to tocilizumab and 1 to adalimumab. Five failed to respond (4 tocilizumab, 1 adalimumab) and one had a minimal response to tocilizumab.

CONCLUSIONS

We report on the systemic treatment response of seven children with ADNIV treated with methotrexate, infliximab, and tocilizumab. None were able to control disease. Further studies are needed to understand long-term outcomes and the utility of systemic immunosuppression.

Autosomal dominant neovascular inflammatory vitreoretinopathy with CAPN5 c.731T > C gene mutation; clinical management of a family cohort and review of the literature

BACKGROUND

To report a cohort of patients with clinically and genetically diagnosed autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV) and showcase the spectrum of the disease utilizing multimodal imaging and genetic testing. Additionally, the utility of multimodal imaging in guiding treatment will also be illustrated.

MATERIALS/METHODS

Five patients from a single-family pedigree in Ohio with clinical signs of ADNIV were evaluated. Medical history, family history, and complete ocular examinations were obtained during regular clinic visits. Multimodal imaging including ocular coherence tomography, fluorescein angiography, wide-field fundus photographs, and Humphrey visual field testing was obtained for all five patients. Additionally, genetic testing for the Calpain-5 (CAPN5) gene was conducted on all patients.

RESULTS

All five patients were noted to have a CAPN5 c.731T > C (p.L244P) mutation on genetic testing. Using multimodal imaging to supplement the clinical examination, pathologic changes such as retinal vascular inflammation, macular edema, and tractional retinal membranes were well illustrated and monitored over time. This allowed for earlier intervention when appropriate such as with intraocular steroid or systemic anti-inflammatory treatments.

CONCLUSION

Phenotypic presentation varied among patients in this series, but is consistent with the spectrum of pathologic changes previously described in patients with other CAPN5 gene mutations. Monitoring of patients with ADNIV utilizing multimodal imaging can help better assess progression of this disease and guide treatment decisions. Additionally, increased genetic testing in patients with inherited retinal diseases may reveal novel gene mutations that could serve as potential targets for future genetic treatment regimens.

Impaired activity and membrane association of most calpain-5 mutants causal for neovascular inflammatory vitreoretinopathy

Neovascular inflammatory vitreoretinopathy (NIV) is a rare eye disease that ultimately leads to complete blindness and is caused by mutations in the gene encoding calpain-5 (CAPN5), with six pathogenic mutations identified. In transfected SH-SY5Y cells, five of the mutations resulted in decreased membrane association, diminished S-acylation, and reduced calcium-induced autoproteolysis of CAPN5. CAPN5 proteolysis of the autoimmune regulator AIRE was impacted by several NIV mutations. R243, L244, K250 and the adjacent V249 are on β-strands in the protease core 2 domain. Conformational changes induced by Ca2+binding result in these β-strands forming a β-sheet and a hydrophobic pocket which docks W286 side chain away from the catalytic cleft, enabling calpain activation based on comparison with the Ca2+-bound CAPN1 protease core. The pathologic variants R243L, L244P, K250N, and R289W are predicted to disrupt the β-strands, β-sheet, and hydrophobic pocket, impairing calpain activation. The mechanism by which these variants impair membrane association is unclear. G376S impacts a conserved residue in the CBSW domain and is predicted to disrupt a loop containing acidic residues which may contribute to membrane binding. G267S did not impair membrane association and resulted in a slight but significant increase in autoproteolytic and proteolytic activity. However, G267S is also identified in individuals without NIV. Combined with the autosomal dominant pattern of NIV inheritance and evidence that CAPN5 may dimerize, the results are consistent with a dominant negative mechanism for the five pathogenic variants which resulted in impaired CAPN5 activity and membrane association and a gain-of-function for the G267S variant.

Calpains as mechanistic drivers and therapeutic targets for ocular disease

Ophthalmic neurodegenerative diseases encompass a wide array of molecular pathologies unified by calpain dysregulation. Calpains are calcium-dependent proteases that perpetuate cellular death and inflammation when hyperactivated. Calpain inhibition trials in other organs have faced pharmacological challenges, but the eye offers many advantages for the development and testing of targeted molecular therapeutics, including small molecules, peptides, engineered proteins, drug implants, and gene-based therapies. This review highlights structural mechanisms underlying calpain activation, distinct cellular expression patterns, and in vivo models that link calpain hyperactivity to human retinal and developmental disease. Optimizing therapeutic approaches for calpain-mediated eye diseases can help accelerate clinically feasible strategies for treating calpain dysregulation in other diseased tissues.

Characterization of mitochondrial calpain-5

Calpain, a Ca²⁺-dependent cysteine protease, plays a significant role in gene expression, signal transduction, and apoptosis. Mutations in human calpain-5 cause autosomal dominant neovascular inflammatory vitreoretinopathy and the inhibition of calpain-5 activity may constitute an effective therapeutic strategy for this condition. Although calpain-5 is ubiquitously expressed in mammalian tissues and was recently found to be present in the mitochondria as well as in the cytosol, its physiological function and enzymological properties require further elucidation. The objective of the current study was to determine the characteristics of mitochondrial calpain-5 in porcine retinas, human HeLa cells, and C57BL/6J mice using subcellular fractionation. We found that mitochondrial calpain-5 was proteolyzed/autolyzed at low Ca²⁺ concentrations in mitochondria isolated from porcine retinas and by thapsigargin-induced endoplasmic reticulum (ER) stress in HeLa cells. Further, mitochondrial calpain-5, as opposed to cytosolic calpain-5, was activated during the early stages of ER stress in C57BL/6J mice. These results showed that mitochondrial calpain-5 was activated at low Ca²⁺ concentrations in vitro and in response to ER stress in vivo. The present study provides new insights into a novel calpain system in the mitochondria that includes stress responses during the early phases of ER stress. Further, activation of mitochondrial calpain-5 by treatment using low-molecular-weight compounds may have therapeutic potential for diseases related to ER stress, including neurodegenerative diseases, metabolic syndromes, diabetes, and cancer.

Whole-Exome Sequencing of Patients With Posterior Segment Uveitis

OBJECTIVE

To elucidate molecular risk factors for posterior segment uveitis using a functional genomics approach.

DESIGN

Genetic association cohort study.

METHODS

Setting: Single-center study at an academic referral center.

STUDY POPULATION

164 patients with clinically diagnosed uveitis of the posterior segment.

MAIN OUTCOME MEASURES

Exome sequencing was used to detect variants identified in 164 patients with posterior segment uveitis. A phenotype-driven analysis, protein structural modeling, and in silico calculations were then used to rank and predict the functional consequences of key variants.

RESULTS

A total of 203 single nucleotide variants, in 23 genes across 164 patients, were included in this study. Both known and novel variants were identified in genes previously implicated in specific types of syndromic uveitis-such as NOD2 (Blau syndrome) and CAPN5 NIV (neovascular inflammatory vitreoretinopathy)-as well as variants in genes not previously linked to posterior segment uveitis. Based on a ranked list and protein-protein-interaction network, missense variants in NOD-like receptor family genes (NOD2, NLRC4, NLRP3, and NLRP1), CAPN5, and TYK2 were characterized via structural modeling and in silico calculations to predict how specific variants might alter protein structure and function. The majority of analyzed variants were notably different from wild type.

CONCLUSIONS

This study implicates new pathways and immune signaling proteins that may be associated with posterior segment uveitis susceptibility. A larger cohort and functional studies will help validate the pathogenicity of the mutations identified. In specific cases, whole-exome sequencing can help diagnose nonsyndromic uveitis in patients harboring known variants for syndromic inflammatory diseases.

Molecular Surgery: Proteomics of a Rare Genetic Disease Gives Insight into Common Causes of Blindness

Rare diseases are an emerging global health priority. Although individually rare, the prevalence of rare "orphan" diseases is high, affecting approximately 300 million people worldwide. Treatments for these conditions are often inadequate, leaving the disease to progress unabated. Here, we review the clinical features and pathophysiology of neovascular inflammatory vitreoretinopathy (NIV), a rare inflammatory retinal disease caused by mutations in the CAPN5 gene. Although the prevalence of NIV is low (1 in 1,000,000 people), the disease mimics more common causes of blindness (e.g. uveitis, retinitis pigmentosa, proliferative diabetic retinopathy, and proliferative vitreoretinopathy) at distinct clinical stages. There is no cure for NIV to date. We highlight how personalized proteomics helped identify potential stage-specific biomarkers and drug targets in liquid vitreous biopsies. The NIV vitreous proteome revealed enrichment of molecular pathways associated with common retinal pathologies and implicated superior targets for therapeutic drug repositioning. In addition, we review our pipeline for collecting, storing, and analyzing ophthalmic surgical samples. This approach can be adapted to treat a variety of rare genetic diseases.

Structural Insights into the Unique Activation Mechanisms of a Non-classical Calpain and Its Disease-Causing Variants

Increased calpain activity is linked to neuroinflammation including a heritable retinal disease caused by hyper-activating mutations in the calcium-activated calpain-5 (CAPN5) protease. Although structures for classical calpains are known, the structure of CAPN5, a non-classical calpain, remains undetermined. Here we report the 2.8 Å crystal structure of the human CAPN5 protease core (CAPN5-PC). Compared to classical calpains, CAPN5-PC requires high calcium concentrations for maximal activity. Structure-based phylogenetic analysis and multiple sequence alignment reveal that CAPN5-PC contains three elongated flexible loops compared to its classical counterparts. The presence of a disease-causing mutation (c.799G>A, p.Gly267Ser) on the unique PC2L2 loop reveals a function in this region for regulating enzymatic activity. This mechanism could be transferred to distant calpains, using synthetic calpain hybrids, suggesting an evolutionary mechanism for fine-tuning calpain function by modifying flexible loops. Further, the open (inactive) conformation of CAPN5-PC provides structural insight into CAPN5-specific residues that can guide inhibitor design.