Functional validation of a human CAPN5 exome variant by lentiviral transduction into mouse retina

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.

Role of calpain-5 in cerebral ischemia and reperfusion injury

BACKGROUND

Ischemia and reperfusion (I/R) injury exacerbate the prognosis of ischemic diseases. The cause of this exacerbation is partly a mitochondrial cell death pathway. Mitochondrial calpain-5 is proteolyzed/autolyzed under endoplasmic reticulum stress, resulting in inflammatory caspase-4 activation. However, the role of calpain-5 in I/R injury remains unclear. We hypothesized that calpain-5 is involved in ischemic brain disease.

METHODS

Mitochondria from C57BL/6J mice were extracted via centrifugation with/without proteinase K treatment. The expression and proteolysis/autolysis of calpain-5 were determined using western blotting. The mouse and human brains with I/R injury were analyzed using hematoxylin and eosin staining and immunohistochemistry. HT22 cells were treated with tunicamycin and CAPN5 siRNA.

RESULTS

Calpain-5 was expressed in the mitochondria of mouse tissues. Mitochondrial calpain-5 in mouse brains was responsive to calcium earlier than cytosolic calpain-5 in vitro calcium assays and in vivo bilateral common carotid artery occlusion model mice. Immunohistochemistry revealed that neurons were positive for calpain-5 in the normal brains of mice and humans. The expression of calpain-5 was increased in reactive astrocytes at human infarction sites. The knockdown of calpain-5 suppressed of cleaved caspase-11.

CONCLUSIONS

The neurons of human and mouse brains express calpain-5, which is proteolyzed/autolyzed in the mitochondria in the early stage of I/R injury and upregulated in reactive astrocytes in the end-stage.

GENERAL SIGNIFICANCE

Our results provide a comprehensive understanding of the mechanisms underlying I/R injury. Targeting the expression or activity of mitochondrial calpain-5 may suppress the inflammation during I/R injuries such as cerebrovascular diseases.

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.

Long-term progression of retinal degeneration in a preclinical model of CLN7 Batten disease as a baseline for testing clinical therapeutics

BACKGROUND

Batten disease is characterized by cognitive and motor impairment, retinal degeneration, and seizures leading to premature death. Recent studies have shown efficacy for a gene therapy approach for CLN7 Batten disease. This gene therapy approach is promising to treat cognitive and motor impairment, but is not likely to delay vision loss. Additionally, the natural progression of retinal degeneration in CLN7 Batten disease patients is not well-known.

METHODS

We performed visual examinations on five patients with CLN7 Batten disease and found that patients were far progressed in degeneration within their first five years of life. To better understand the disease progression, we characterized the retina of a preclinical mouse model of CLN7 Batten disease, through the age at which mice present with paralysis and premature death.

FINDINGS

We found that this preclinical model shows signs of photoreceptor to bipolar synaptic defects early, and displays rod-cone dystrophy with late loss of bipolar cells. This vision loss could be followed not only via histology, but using clinical live imaging similar to that used in human patients.

INTERPRETATION

Natural history studies of rare paediatric neurodegenerative conditions are complicated by the rapid degeneration and limited availability of patients. Characterization of degeneration in the preclinical model allows for future experiments to better understand the mechanisms underlying the retinal disease progression in order to find therapeutics to treat patients, as well as to evaluate these therapeutic options for future human clinical trials.

FUNDING

Van Sickle Family Foundation Inc., NIHP30EY030413, Morton Fichtenbaum Charitable Trust and 5T32GM131945-03.

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.

Long-Term Outcomes and Risk Factors for Severe Vision Loss in Autosomal Dominant Neovascular Inflammatory Vitreoretinopathy (ADNIV)

Autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV) is a rare disorder characterized by uveitis, retinal neovascularization, and retinal degeneration. We sought to describe the course of treated and untreated ADNIV and to identify risk factors for severe vision loss.

DESIGN

Observational case series.

METHODS

Clinical data from ADNIV patients from 4 families seen from 1967 through 2019 at a single academic, tertiary referral center were reviewed. The main outcome measures were visual acuity at baseline and follow-up, as well as risk factors for vision loss.

RESULTS

A total of 130 eyes from 65 ADNIV patients (45 female, 20 male; mean age 40.8 years, range 6-77 years) were included. Mean best corrected visual acuity (BCVA) at presentation was LogMAR 0.59 (about Snellen 20/80). Longitudinal analysis included 84 eyes from 42 patients (31 female, 11 male), with mean follow-up of 17.3 years (range 2-43.6 years). Mean BCVA at last follow-up was LogMAR 1.48 (about Snellen 20/600). The disease accelerated in the fifth decade of life, during which the majority of eyes went from normal vision or mild vision loss to at least moderate vision loss (20/70 Snellen equivalent); 25 eyes from 16 patients (29.8%;) showed a steep trajectory of vision loss to no light perception. Tractional retinal detachment was the greatest risk factor for severe vision loss (BCVA <20/200) on multivariable analysis (P < .05).

CONCLUSIONS

Patients with ADNIV have a high lifetime risk of severe vision loss. Tractional retinal detachment is an important risk factor for poor vision.

PROGRESSION OF SCOTOPIC SINGLE-FLASH ELECTRORETINOGRAPHY IN THE STAGES OF CAPN5 VITREORETINOPATHY

PURPOSE

To characterize the changes found in the electroretinography (ERG) recordings of patients with autosomal dominant neovascular inflammatory vitreoretinopathy and correlate with clinical stages of the disease.

METHODS

Retrospective chart review. Bright- and dim-flash full-field scotopic, photopic, and 30-Hz flicker ERGs were obtained according to international standards. The scotopic ERGs were further processed to analyze the oscillatory potential. The patient described in the case report underwent full ERG testing; five patients composed the archival case series data and included scotopic ERG recordings.

RESULTS

Stage I autosomal dominant neovascular inflammatory vitreoretinopathy is characterized by a decrease in the b-wave amplitude on scotopic flash ERG and the disappearance of late OPs; however, the a-wave amplitude is normal. In Stage II, attenuation of early OPs and the c-wave are observed in scotopic ERG recordings, but both a- and b-wave amplitudes are unchanged. For patients in Stage III, there is a continued decline of both a- and b-wave amplitudes in scotopic ERG recordings. There was a loss of recordable scotopic ERG response in patients with Stage IV disease.

CONCLUSION

Electroretinography may be valuable in determining optimal timing for therapeutic intervention and response before loss of recordable retinal function in CAPN5 vitreoretinopathy.

Piccolo is essential for the maintenance of mouse retina but not cochlear hair cell function

Piccolo is a presynaptic protein with high conservation among different species, and the expression of Piccolo is extensive in vertebrates. Recently, a small fragment of Piccolo (Piccolino), arising due to the incomplete splicing of intron 5/6, was found to be present in the synapses of retinas and cochleae. However, the comprehensive function of Piccolo in the retina and cochlea remains unclear. In this study, we generated Piccolo knockout mice using CRISPR-Cas9 technology to explore the function of Piccolo. Unexpectedly, whereas no abnormalities were found in the cochlear hair cells of the mutant mice, significant differences were found in the retinas, in which two layers (the outer nuclear layer and the outer plexiform layer) were absent. Additionally, the amplitudes of electroretinograms were significantly reduced and pigmentation was observed in the fundoscopy of the mutant mouse retinas. The expression levels of Bassoon, a homolog of Piccolo, as well as synapse-associated proteins CtBP1, CtBP2, Kif3A, and Rim1 were down-regulated. The numbers of ribbon synapses in the retinas of the mutant mice were also reduced. Altogether, the phenotype of Piccolo-/- mice resembled the symptoms of retinitis pigmentosa (RP) in humans, suggesting Piccolo might be a candidate gene of RP and indicates Piccolo knockout mice are a good model for elucidating the molecular mechanisms of RP.

The C2 domain of calpain 5 contributes to enzyme activation and membrane localization

The enzymatic characteristics of the ubiquitous calpain 5 (CAPN5) remain undescribed despite its high expression in the central nervous system and links to eye development and disease. CAPN5 contains the typical protease core domains but lacks the C terminal penta-EF hand domain of classical calpains, and instead contains a putative C2 domain. This study used the SH-SY5Y neuroblastoma cell line stably transfected with CAPN5-3xFLAG variants to assess the potential roles of the CAPN5 C2 domain in Ca²⁺ regulated enzyme activity and intracellular localization. Calcium dependent autoproteolysis of CAPN5 was documented and characterized. Mutation of the catalytic Cys81 to Ala or addition of EGTA prevented autolysis. Eighty μM Ca²⁺ was sufficient to stimulate half-maximal CAPN5 autolysis in cellular lysates. CAPN5 autolysis was inhibited by tri-leucine peptidyl aldehydes, but less effectively by di-Leu aldehydes, consistent with a more open conformation of the protease core relative to classical calpains. In silico modeling revealed a type II topology C2 domain including loops with the potential to bind calcium. Mutation of the acidic amino acid residues predicted to participate in Ca²⁺ binding, particularly Asp531 and Asp589, resulted in a decrease of CAPN5 membrane association. These residues were also found to be invariant in several genomes. The autolytic fragment of CAPN5 was prevalent in membrane-enriched fractions, but not in cytosolic fractions, suggesting that membrane association facilitates the autoproteolytic activity of CAPN5. Together, these results demonstrate that CAPN5 undergoes Ca²⁺-activated autoproteolytic processing and suggest that CAPN5 association with membranes enhances CAPN5 autolysis.

Effects of functionally diverse calpain system on immune cells

Calpains are a family of nonlysosomal cysteine proteases, which play important roles in numerous physiological and pathological processes. Locations of them dictates the functions so that they are classified as ubiquitously expressed calpains and tissue-specific calpains. Recent studies are mainly focused on conventional calpains (calpain-1,2) in development and diseases, and increasing people pay attention to other subtypes of calpains but may not been summarized appropriately. Growing evidence suggests that calpains are also involved in immune regulation. However, seldom articles review the regulation of calpains on immune cells. The aim of this article is to review the research progress of each calpain isozyme and the effect of calpains on immune cells, especially the promotion effect of calpains on the immune response of macrophage, neutrophils, dendritic cells, mast cells, natural killed cells, and lymphocytes. These effects would hold great promise for the clinical application of calpains as a practicable therapeutic option in the treatment of immune related diseases.

Biallelic deletion in a minimal CAPN15 intron in siblings with a recognizable syndrome of congenital malformations and developmental delay

Calpainopathies constitute a heterogeneous group of disorders resulting from deficiencies in calpains, calcium-specific proteases that modulate substrates by limited proteolysis. Clinical manifestations depend on tissue-specific expression of the defective calpain and substrate specificity. CAPN15, encoding the Drosophila small optic lobes (sol) homolog, was recently found to cause various eye defects in individuals carrying bi-allelic missense variants. Here we report on two siblings with manifestations reminiscent of Johanson-Blizzard syndrome including failure to thrive, microcephaly, global developmental delay, dysmorphic features, endocrine abnormalities and congenital malformations, in addition to eye abnormalities. Exome sequencing identified a homozygous 47 base-pair deletion in a minimal intron of CAPN15, including the splice donor site. Sequencing of cDNA revealed single exon skipping, resulting in an out-of-frame deletion with a predicted premature termination codon. These findings expand the phenotypic spectrum associated with CAPN15 variants, and suggest that complete loss-of-function is associated with a recognizable syndrome of congenital malformations and developmental delay, overlapping Johanson-Blizzard syndrome and the recently observed brain defects in Capn15 knockout (KO) mice. Moreover, the data highlight the unique opportunity for indel detection in minimal introns.

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.

Phenotypic variance in Calpain-5 retinal degeneration

Purpose

To characterize the phenotype of patients with mild calpain-5 Neovascular Inflammatory Vitreoretinopathy (ADNIV).

Observations

The CAPN5 p.R243L mutation is typically associated with onset in the twenties and severe, progressive uveitis, retinal neovascularization, and intraocular fibrosis. Two subjects with this CAPN5 variant only showed mild peripheral retinal pigmentary degeneration and loss of the ERG b-wave at age 45 and 69, respectively, without signs of uveitis or neovascularization.

Conclusions/Importance

The phenotypic penetrance of a specific variant in CAPN5-vitreoretinopathy may vary significantly in severity. Patients with pigmentary retinal dystrophy may consider CAPN5 gene testing.

Metabolite therapy guided by liquid biopsy proteomics delays retinal neurodegeneration

Background

Neurodegenerative diseases are incurable disorders caused by progressive neuronal cell death. Retinitis pigmentosa (RP) is a blinding neurodegenerative disease that results in photoreceptor death and progresses to the loss of the entire retinal network. We previously found that proteomic analysis of the adjacent vitreous served as way to indirectly biopsy the retina and identify changes in the retinal proteome.

Methods

We analyzed protein expression in liquid vitreous biopsies from autosomal recessive (ar)RP patients with PDE6A mutations and arRP mice with Pde6ɑ mutations. Proteomic analysis of retina and vitreous samples identified molecular pathways affected at the onset of photoreceptor death. Based on affected molecular pathways, arRP mice were treated with a ketogenic diet or metabolites involved in fatty-acid synthesis, oxidative phosphorylation, and the tricarboxylic acid (TCA) cycle.

Findings

Dietary supplementation of a single metabolite, ɑ-ketoglutarate, increased docosahexaeonic acid levels, provided neuroprotection, and enhanced visual function in arRP mice. A ketogenic diet delayed photoreceptor cell loss, while vitamin B supplementation had a limited effect. Finally, desorption electrospray ionization mass spectrometry imaging (DESI-MSI) on ɑ-ketoglutarate-treated mice revealed restoration of metabolites that correlated with our proteomic findings: uridine, dihydrouridine, and thymidine (pyrimidine and purine metabolism), glutamine and glutamate (glutamine/glutamate conversion), and succinic and aconitic acid (TCA cycle).

Interpretation

This study demonstrates that replenishing TCA cycle metabolites via oral supplementation prolongs retinal function and provides a neuroprotective effect on the photoreceptor cells and inner retinal network.

Funding

NIH grants [R01EY026682, R01EY024665, R01EY025225, R01EY024698, R21AG050437, P30EY026877, 5P30EY019007, R01EY018213, F30EYE027986, T32GM007337, 5P30CA013696], NSF grant CHE-1734082.

CAPN5 genetic inactivation phenotype supports therapeutic inhibition trials

Small molecule pharmacological inhibition of dominant human genetic disease is a feasible treatment that does not rely on the development of individual, patient-specific gene therapy vectors. However, the consequences of protein inhibition as a clinical therapeutic are not well-studied. In advance of human therapeutic trials for CAPN5 vitreoretinopathy, genetic inactivation can be used to infer the effect of protein inhibition in vivo. We created a photoreceptor-specific knockout (KO) mouse for Capn5 and compared the retinal phenotype to both wild-type and an existing Capn5 KO mouse model. In humans, CAPN5 loss-of-function (LOF) gene variants were ascertained in large exome databases from 60,706 unrelated subjects without severe disease phenotypes. Ocular examination of the retina of Capn5 KO mice by histology and electroretinography showed no significant abnormalities. In humans, there were 22 LOF CAPN5 variants located throughout the gene and in all major protein domains. Structural modeling of coding variants showed these LOF variants were nearby known disease-causing variants within the proteolytic core and in regions of high homology between human CAPN5 and 150 homologs, yet the LOF of CAPN5 was tolerated as opposed to gain-of-function disease-causing variants. These results indicate that localized inhibition of CAPN5 is a viable strategy for hyperactivating disease alleles.

Proteomic insight into the pathogenesis of CAPN5-vitreoretinopathy

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.

In Vivo Expression of Mutant Calpains in the Eye Using Lentivirus

Exome sequencing has identified many candidate genes and mutations for human diseases, but the functional validation of these candidates is a time-consuming and costly process. Here, we describe a method which uses lentiviruses to overexpress calpain mutations that may play a role in dominant diseases such as autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV). The use of lentivirus to deliver the mutant calpain allows for a cost-effective, rapid, and efficient approach to test whether or not a candidate gene mutation from exome sequencing acts as the disease-causing allele for a human disorder. This method also provides for a comparison of different candidate mutations from a single gene identified by exome sequencing, as well as elucidating the mechanisms underlying these complex human disorders. Furthermore, this chapter focuses on two different methods to deliver mutant calpain to the cells of the eye, using either a subretinal or an intravitreal injection of the lentivirus into the mouse eye.

Capn5 Expression in the Healthy and Regenerating Zebrafish Retina

Purpose

Autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV) is a devastating inherited autoimmune disease of the eye that displays features commonly seen in other eye diseases, such as retinitis pigmentosa and diabetic retinopathy. ADNIV is caused by a gain-of-function mutation in Calpain-5 (CAPN5), a calcium-dependent cysteine protease. Very little is known about the normal function of CAPN5 in the adult retina, and there are conflicting results regarding its role during mammalian embryonic development. The zebrafish (Danio rerio) is an excellent animal model for studying vertebrate development and tissue regeneration, and represents a novel model to explore the function of Capn5 in the eye.

Methods

We characterized the expression of Capn5 in the developing zebrafish central nervous system (CNS) and retina, in the adult zebrafish retina, and in response to photoreceptor degeneration and regeneration using whole-mount in situ hybridization, FISH, and immunohistochemistry.

Results

In zebrafish, capn5 is strongly expressed in the developing embryonic brain, early optic vesicles, and in newly differentiated retinal photoreceptors. We found that expression of capn5 colocalized with cone-specific markers in the adult zebrafish retina. We observed an increase in expression of Capn5 in a zebrafish model of chronic rod photoreceptor degeneration and regeneration. Acute light damage to the zebrafish retina was accompanied by an increase in expression of Capn5 in the surviving cones and in a subset of Müller glia.

Conclusions

These studies suggest that Capn5 may play a role in CNS development, photoreceptor maintenance, and photoreceptor regeneration.

Calpain-5 gene expression in the mouse eye and brain

Objective

Our objective was to characterize CAPN5 gene expression in the mouse central nervous system. Mouse brain and eye sections were probed with two high-affinity RNA oligonucleotide analogs designed to bind CAPN5 RNA and one scramble, control oligonucleotide. Images were captured in brightfield.

Results

CAPN5 RNA probes were validated on mouse breast cancer tumor tissue. In the eye, CAPN5 was expressed in the ganglion cell, inner nuclear and outer nuclear layers of the retina. Signal could not be detected in the ciliary body or the iris because of the high density of melanin. In the brain, CAPN5 was expressed in the granule cell layers of the hippocampus and cerebellum. There was scattered expression in pons. The visual cortex showed faint signal. Most signal in the brain was in a punctate pattern.

An anti-CAPN5 intracellular antibody acts as an inhibitor of CAPN5-mediated neuronal degeneration

CAPN5 has been linked to autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV). Activation of CAPN5 may increase proteolysis and degradation of a wide range of substrates to induce degeneration in the retina and the nerve system. Thus, we developed an inhibitory intracellular single chain variable fragment (scFv) against CAPN5 as a potential way to rescue degeneration in ADNIV disease or in neuronal degeneration. We report that overexpression CAPN5 increases the levels of the auto-inflammatory factors toll like receptor 4 (TLR4), interleukin 1 alpha (IL1alpha), tumor necrosis factor alpha (TNFalpha) and activated caspase 3 in 661W photoreceptor-like cells and SHSY5Y neuronal-like cells. Both C4 and C8 scFvs specifically recognize human/mouse CAPN5 in 661W cells and SHSY5Y cells, moreover, both the C4 and C8 scFvs protected cells from CAPN5-induced apoptosis by reducing the levels of activated caspase 3 and caspase 9. The cellular expression C4 scFv reduced levels of the pro-inflammatory factor IL1-alpha activated caspase 3 in cells after CAPN5 overexpression. We suggest that CAPN5 expression has important functional consequences in auto-inflammatory processes, and apoptosis in photoreceptor like cells and neural-like cells. Importantly, the specific intracellular targeting of antibody fragments blocking activation of CAPN5 act as inhibitors of CAPN5 functions in neural like cells, thus, our data provides a novel potential tool for therapy in CAPN5-mediated ADNIV or neurodegenerative diseases.

Two Novel CAPN5 Variants Associated with Mild and Severe Autosomal Dominant Neovascular Inflammatory Vitreoretinopathy Phenotypes

Purpose: We report two new CAPN5 mutations associated with a phenotype of Autosomal Dominant Neovascular Inflammatory Vitreoretinopathy. Methods: We performed next generation sequencing in two patients with ADNIV phenotype; the variants identified were explored further. Results: Patient 1 was heterozygous for CAPN5 c.799G>A, p.(Gly267Ser). Patient 2 was heterozygous for CAPN5 c.1126G>A, p.(Gly376Ser). Both amino acids are highly conserved across species. Patient 1 had a severe phenotype and his mutation lies within the protein's catalytic domain. Patient 2 had a mild phenotype and her mutation is the first ADNIV-causing mutation to be described in the regulatory domain of Calpain-5. Conclusions: Our findings potentially add two new ADNIV-causing CAPN5 mutations to the three previously described. We recommend CAPN5 genetic testing in all patients with a possible ADNIV phenotype, to develop our understanding of Calpain-5; a protein which could potentially provide therapeutically accessible targets for the treatment of many leading causes of blindness.

Calpain-5 Expression in the Retina Localizes to Photoreceptor Synapses

Purpose

We characterize calpain-5 (CAPN5) expression in retinal and neuronal subcellular compartments.

Methods

CAPN5 gene variants were classified using the exome variant server, and RNA-sequencing was used to compare expression of CAPN5 mRNA in the mouse and human retina and in retinoblastoma cells. Expression of CAPN5 protein was ascertained in humans and mice in silico, in mouse retina by immunohistochemistry, and in neuronal cancer cell lines and fractionated central nervous system tissue extracts by Western analysis with eight antibodies targeting different CAPN5 regions.

Results

Most CAPN5 genetic variation occurs outside its protease core; and searches of cancer and epilepsy/autism genetic databases found no variants similar to hyperactivating retinal disease alleles. The mouse retina expressed one transcript for CAPN5 plus those of nine other calpains, similar to the human retina. In Y79 retinoblastoma cells, the level of CAPN5 transcript was very low. Immunohistochemistry detected CAPN5 expression in the inner and outer nuclear layers and at synapses in the outer plexiform layer. Western analysis of fractionated retinal extracts confirmed CAPN5 synapse localization. Western blots of fractionated brain neuronal extracts revealed distinct subcellular patterns and the potential presence of autoproteolytic CAPN5 domains.

Conclusions

CAPN5 is moderately expressed in the retina and, despite higher expression in other tissues, hyperactive disease mutants of CAPN5 only manifest as eye disease. At the cellular level, CAPN5 is expressed in several different functional compartments. CAPN5 localization at the photoreceptor synapse and with mitochondria explains the neural circuitry phenotype in human CAPN5 disease alleles.

Small-angle X-ray scattering of calpain-5 reveals a highly open conformation among calpains

Calpain-5 is a calcium-activated protease expressed in the retina. Mutations in calpain-5 cause autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV, OMIM#193235). The structure of calpain-5 has not been determined, thus hindering the investigation of its proteolytic targets and pathological role in ADNIV. Herein, we report models of the proteolytic core of calpain-5 (mini-calpain-5) containing two globular domains (termed DIIa-IIb) connected by a short, flexible linker, consistent with small-angle X-ray scattering (SAXS) data. Structural modeling in the absence of calcium suggests that mini-calpain-5 adopts a more open conformation when compared to previously determined structures of other calpain cores. This open conformation, achieved by a rotation of DIIa and DIIb with respect to each other, prevents formation of the active site and constrains the enzyme in an inactivated form. The relative domain rotation of 60-100° we found for mini-calpain-5 (a non-classical calpain) is significantly greater than the largest rotation previously observed for a classical calpain (i.e., 55.0° for mini-calpain-9). Together with our prediction that, in the full-length form, a long loop in DIIb (loop C1), a few residues downstream of the inter-domain linker, likely interacts with the shorter, acidic, inactivating loop on domain-III (DIII), these structural insights illuminate the complexity of calpain regulation. Moreover, our studies argue that pursuing higher resolution structural studies are necessary to understand the complex activity regulation prevalent in the calpain family and for the design of specific calpain inhibitors.

CRISPR Repair Reveals Causative Mutation in a Preclinical Model of Retinitis Pigmentosa

Massive parallel sequencing enables identification of numerous genetic variants in mutant organisms, but determining pathogenicity of any one mutation can be daunting. The most commonly studied preclinical model of retinitis pigmentosa called the "rodless" (rd1) mouse is homozygous for two mutations: a nonsense point mutation (Y347X) and an intronic insertion of a leukemia virus (Xmv-28). Distinguishing which mutation causes retinal degeneration is still under debate nearly a century after the discovery of this model organism. Here, we performed gene editing using the CRISPR/Cas9 system and demonstrated that the Y347X mutation is the causative variant of disease. Genome editing in the first generation produced animals that were mosaic for the corrected allele but still showed neurofunction preservation despite low repair frequencies. Furthermore, second-generation CRISPR-repaired mice showed an even more robust rescue and amelioration of the disease. This predicts excellent outcomes for gene editing in diseased human tissue, as Pde6b, the mutated gene in rd1 mice, has an orthologous intron-exon relationship comparable with the human PDE6B gene. Not only do these findings resolve the debate surrounding the source of neurodegeneration in the rd1 model, but they also provide the first example of homology-directed recombination-mediated gene correction in the visual system.

Neuroretinal hypoxic signaling in a new preclinical murine model for proliferative diabetic retinopathy

Diabetic retinopathy (DR) affects approximately one-third of diabetic patients and, if left untreated, progresses to proliferative DR (PDR) with associated vitreous hemorrhage, retinal detachment, iris neovascularization, glaucoma and irreversible blindness. In vitreous samples of human patients with PDR, we found elevated levels of hypoxia inducible factor 1 alpha (HIF1α). HIFs are transcription factors that promote hypoxia adaptation and have important functional roles in a wide range of ischemic and inflammatory diseases. To recreate the human PDR phenotype for a preclinical animal model, we generated a mouse with neuroretinal-specific loss of the von Hippel Lindau tumor suppressor protein, a protein that targets HIF1α for ubiquitination. We found that the neuroretinal cells in these mice overexpressed HIF1α and developed severe, irreversible ischemic retinopathy that has features of human PDR. Rapid progression of retinopathy in these mutant mice should facilitate the evaluation of therapeutic agents for ischemic and inflammatory blinding disorders. In addition, this model system can be used to manipulate the modulation of the hypoxia signaling pathways, for the treatment of non-ocular ischemic and inflammatory disorders.

CAPN5 mutation in hereditary uveitis: the R243L mutation increases calpain catalytic activity and triggers intraocular inflammation in a mouse model

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.

Between Rho(k) and a hard place: the relation between vessel wall stiffness, endothelial contractility, and cardiovascular disease

Vascular stiffness is a mechanical property of the vessel wall that affects blood pressure, permeability, and inflammation. As a result, vascular stiffness is a key driver of (chronic) human disorders, including pulmonary arterial hypertension, kidney disease, and atherosclerosis. Responses of the endothelium to stiffening involve integration of mechanical cues from various sources, including the extracellular matrix, smooth muscle cells, and the forces that derive from shear stress of blood. This response in turn affects endothelial cell contractility, which is an important property that regulates endothelial stiffness, permeability, and leukocyte-vessel wall interactions. Moreover, endothelial stiffening reduces nitric oxide production, which promotes smooth muscle cell contraction and vasoconstriction. In fact, vessel wall stiffening, and microcirculatory endothelial dysfunction, precedes hypertension and thus underlies the development of vascular disease. Here, we review the cross talk among vessel wall stiffening, endothelial contractility, and vascular disease, which is controlled by Rho-driven actomyosin contractility and cellular mechanotransduction. In addition to discussing the various inputs and relevant molecular events in the endothelium, we address which actomyosin-regulated changes at cell adhesion complexes are genetically associated with human cardiovascular disease. Finally, we discuss recent findings that broaden therapeutic options for targeting this important mechanical signaling pathway in vascular pathogenesis.

Structural modeling of a novel CAPN5 mutation that causes uveitis and neovascular retinal detachment

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.

CAPN5 gene silencing by short hairpin RNA interference

BACKGROUND

The purpose of this project was to identify short hairpin RNA (shRNA) sequences that can suppress expression of human CAPN5 in which gain-of-function mutants cause autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV). We created HEK293T cells that stably express an ADNIV disease allele, CAPN5-p.R243L. Transfection protocols were optimized for neuroblastoma SHSY5Y cells. The gene silencing effect of four different shRNA plasmids that target CAPN5 was tested. RNA and protein expression was determined using quantitative RT-PCR and immunoblot analysis.

FINDINGS

Two of four shRNA plasmids reduced mutant CAPN5 RNA in a stable cell line. Similar knockdown was observed in SH-SY5Y cells that natively express CAPN5. Lactose dehydrogenase assays showed that down-regulation of CAPN5 was not cytotoxic.

CONCLUSIONS

CAPN5 expression can be suppressed by shRNA-based RNA interference. Further testing in ADNIV models will determine the potential of gene silencing as a strategy to treat, delay, or prevent blindness in ADNIV patients.