AAV2 vector optimization for retinal ganglion cell-targeted delivery of therapeutic genes.

Recombinant adeno-associated virus (AAV)-2 has significant potential as a delivery vehicle of therapeutic genes to retinal ganglion cells (RGCs), which are key interventional targets in optic neuropathies. Here we show that when injected intravitreally, AAV2 engineered with a reporter gene driven by cytomegalovirus (CMV) enhancer and chicken ß-actin (CBA) promoters, displays ubiquitous and high RGC expression, similar to its synthetic derivative AAV8BP2. A novel AAV2 vector combining the promoter of the human RGC-selective γ-synuclein (hSNCG) gene and woodchuck hepatitis post-transcriptional regulatory element (WPRE) inserted upstream and downstream of a reporter gene, respectively, induces widespread transduction and strong transgene expression in RGCs. High transduction efficiency and selectivity to RGCs is further achieved by incorporating in the vector backbone a leading CMV enhancer and an SV40 intron at the 5' and 3' ends, respectively, of the reporter gene. As a delivery vehicle of hSIRT1, a 2.2-kb therapeutic gene with anti-apoptotic, anti-inflammatory and anti-oxidative stress properties, this recombinant vector displayed improved transduction efficiency, a strong, widespread and selective RGC expression of hSIRT1, and increased RGC survival following optic nerve crush. Thus, AAV2 vector carrying hSNCG promoter with additional regulatory sequences may offer strong potential for enhanced effects of candidate gene therapies targeting RGCs.

Repeat Brn3a immunolabeling rescues faded staining and improves detection of retinal ganglion cells.

Immunofluorescence is used in numerous research areas including eye research to detect specific antigens in cells and tissues. One limitation is that fluorescent signal can fade, causing detection problems if data recording was not completed in a timely manner or if additional data acquisition is required. The ability to repeat immunostaining for the same antigen after initial fluorescence has faded may require time-consuming and potentially damaging steps to remove primary antibodies. Our studies assessed whether immunofluorescence could be reapplied to previously labeled retinal ganglion cells (RGCs). To examine whether immunostaining of Brn3a, a commonly used RGC marker, could be repeated in retinas with previously faded immunostaining, retinal whole mounts were labeled with anti-Brn3a primary antibodies and green fluorescent secondary antibodies, then allowed to fade over time. Faded retinas were restained with anti-Brn3a antibody followed by secondary antibody, or with secondary antibody alone. Results show restaining with anti-Brn3a primary antibody followed by Alexa-fluor green secondary antibody is effective for RGC detection. Repeat RGC labeling improved the clarity of staining compared with original staining prior to fading, with significant reduction in the percentage of blurry/out of focus fluorescent cells (6 vs 26%); whereas, repeat application of secondary antibody alone was not effective. Preflattening retinas under a coverslip prior to initial Brn3a staining also increased the clarity of staining, and facilitated significantly more accurate automated counting of RGCs. Findings suggest Brn3a antigen remains accessible for repeat immunofluorescence labeling after original staining fades. Staining retinas after flattening tissue may enhance the clarity of staining and accuracy of automated RGC counting. Repeat immunofluorescence staining, without the need to strip off prior bound antibodies, may be useful in other tissues as well and warrants future examination.

Emerging Gene Therapy Technologies for Retinal Ganglion Cell Neuroprotection.

ABSTRACT: Optic neuropathies encompass a breadth of diseases that ultimately result in dysfunction and/or loss of retinal ganglion cells (RGCs). Although visual impairment from optic neuropathies is common, there is a lack of effective clinical treatments. Addressing a critical need for novel interventions, preclinical studies have been generating a growing body of evidence that identify promising new drug-based and cell-based therapies. Gene therapy is another emerging therapeutic field that offers the potential of specifically and robustly increasing long-term RGC survival in optic neuropathies. Gene therapy offers additional benefits of driving improvements following a single treatment administration, and it can be designed to target a variety of pathways that may be involved in individual optic neuropathies or across multiple etiologies. This review explores the history of gene therapy, the fundamentals of its application, and the emerging development of gene therapy technology as it relates to treatment of optic neuropathies.

Active Rap1-mediated inhibition of choroidal neovascularization requires interactions with IQGAP1 in choroidal endothelial cells.

Neovascular age-related macular degeneration (nAMD) is a leading cause of blindness. The pathophysiology involves activation of choroidal endothelial cells (CECs) to transmigrate the retinal pigment epithelial (RPE) monolayer and form choroidal neovascularization (CNV) in the neural retina. The multidomain GTPase binding protein, IQGAP1, binds active Rac1 and sustains activation of CECs, thereby enabling migration associated with vision-threatening CNV. IQGAP1 also binds the GTPase, Rap1, which when activated reduces Rac1 activation in CECs and CNV. In this study, we tested the hypothesis that active Rap1 binding to IQGAP1 is necessary and sufficient to reduce Rac1 activation in CECs, and CNV. We found that pharmacologic activation of Rap1 or adenoviral transduction of constitutively active Rap1a reduced VEGF-mediated Rac1 activation, migration, and tube formation in CECs. Following pharmacologic activation of Rap1, VEGF-mediated Rac1 activation was reduced in CECs transfected with an IQGAP1 construct that increased active Rap1-IQGAP1 binding but not in CECs transfected with an IQGAP1 construct lacking the Rap1 binding domain. Specific knockout of IQGAP1 in endothelial cells reduced laser-induced CNV and Rac1 activation in CNV lesions, but pharmacologic activation of Rap1 did not further reduce CNV compared to littermate controls. Taken together, our findings provide evidence that active Rap1 binding to the IQ domain of IQGAP1 is sufficient to interfere with active Rac1-mediated CEC activation and CNV formation.

Abscisic acid - an anti-angiogenic phytohormone that modulates the phenotypical plasticity of endothelial cells and macrophages.

Abscisic acid (ABA) has shown anti-inflammatory and immunoregulatory properties in preclinical models of diabetes and inflammation. Herein, we studied the effects of ABA on angiogenesis, a strictly controlled process that, when dysregulated, leads to severe angiogenic disorders including vascular overgrowth, exudation, cellular inflammation and organ dysfunction. By using a 3D sprouting assay, we show that ABA effectively inhibits migration, growth and expansion of endothelial tubes without affecting cell viability. Analyses of the retinal vasculature in developing normoxic and hyperoxic mice challenged by oxygen toxicity reveal that exogenously administered ABA stunts the development and regeneration of blood vessels. In these models, ABA downregulates endothelial cell (EC)-specific growth and migratory genes, interferes with tip and stalk cell specification, and hinders the function of filopodial protrusions required for precise guidance of vascular sprouts. In addition, ABA skews macrophage polarization towards the M1 phenotype characterized by anti-angiogenic marker expression. In accordance with this, ABA treatment accelerates macrophage-induced programmed regression of fetal blood vessels. These findings reveal protective functions of ABA against neovascular growth through modulation of EC and macrophage plasticity, suggesting the potential utility of ABA as a treatment in vasoproliferative diseases.

Eyeing the Extracellular Matrix in Vascular Development and Microvascular Diseases and Bridging the Divide between Vascular Mechanics and Function.

The extracellular matrix (ECM) is critical in all aspects of vascular development and health: supporting cell anchorage, providing structure, organization and mechanical stability, and serving as a sink for growth factors and sustained survival signals. Abnormal changes in ECM protein expression, organization, and/or properties, and the ensuing changes in vascular compliance affect vasodilator responses, microvascular pressure transmission, and collateral perfusion. The changes in microvascular compliance are independent factors initiating, driving, and/or exacerbating a plethora of microvascular diseases of the eye including diabetic retinopathy (DR) and vitreoretinopathy, retinopathy of prematurity (ROP), wet age-related macular degeneration (AMD), and neovascular glaucoma. Congruently, one of the major challenges with most vascular regenerative therapies utilizing localized growth factor, endothelial progenitor, or genetically engineered cell delivery, is the regeneration of blood vessels with physiological compliance properties. Interestingly, vascular cells sense physical forces, including the stiffness of their ECM, through mechanosensitive integrins, their associated proteins and the actomyosin cytoskeleton, which generates biochemical signals that culminate in a rapid expression of matricellular proteins such as cellular communication network 1 (CCN1) and CCN2 (aka connective tissue growth factor or CTGF). Loss or gain of function of these proteins alters genetic programs of cell growth, ECM biosynthesis, and intercellular signaling, that culminate in changes in cell behavior, polarization, and barrier function. In particular, the function of the matricellular protein CCN2/CTGF is critical during retinal vessel development and regeneration wherein new blood vessels form and invest a preformed avascular neural retina following putative gradients of matrix stiffness. These observations underscore the need for further in-depth characterization of the ECM-derived cues that dictate structural and functional properties of the microvasculature, along with the development of new therapeutic strategies addressing the ECM-dependent regulation of pathophysiological stiffening of blood vessels in ischemic retinopathies.

The matricellular protein CCN1 controls retinal angiogenesis by targeting VEGF, Src homology 2 domain phosphatase-1 and Notch signaling.

Physiological angiogenesis depends on the highly coordinated actions of multiple angiogenic regulators. CCN1 is a secreted cysteine-rich and integrin-binding matricellular protein required for proper cardiovascular development. However, our understanding of the cellular origins and activities of this molecule is incomplete. Here, we show that CCN1 is predominantly expressed in angiogenic endothelial cells (ECs) at the leading front of actively growing vessels in the mouse retina. Endothelial deletion of CCN1 in mice using a Cre-Lox system is associated with EC hyperplasia, loss of pericyte coverage and formation of dense retinal vascular networks lacking the normal hierarchical arrangement of arterioles, capillaries and venules. CCN1 is a product of an immediate-early gene that is transcriptionally induced in ECs in response to stimulation by vascular endothelial growth factor (VEGF). We found that CCN1 activity is integrated with VEGF receptor 2 (VEGF-R2) activation and downstream signaling pathways required for tubular network formation. CCN1-integrin binding increased the expression of and association between Src homology 2 domain-containing protein tyrosine phosphatase-1 (SHP-1) and VEGF-R2, which leads to rapid dephosphorylation of VEGF-R2 tyrosine, thus preventing EC hyperproliferation. Predictably, CCN1 further brings receptors/signaling molecules into proximity that are otherwise spatially separated. Furthermore, CCN1 induces integrin-dependent Notch activation in cultured ECs, and its targeted gene inactivation in vivo alters Notch-dependent vascular specification and remodeling, suggesting that functional levels of Notch signaling requires CCN1 activity. These data highlight novel functions of CCN1 as a naturally optimized molecule, fine-controlling key processes in physiological angiogenesis and safeguarding against aberrant angiogenic responses.

Single and Compound Knock-outs of MicroRNA (miRNA)-155 and Its Angiogenic Gene Target CCN1 in Mice Alter Vascular and Neovascular Growth in the Retina via Resident Microglia.

The response of the retina to ischemic insult typically leads to aberrant retinal neovascularization, a major cause of blindness. The epigenetic regulation of angiogenic gene expression by miRNAs provides new prospects for their therapeutic utility in retinal neovascularization. Here, we focus on miR-155, a microRNA functionally important in inflammation, which is of paramount importance in the pathogenesis of retinal neovascularization. Whereas constitutive miR-155-deficiency in mice results in mild vascular defects, forced expression of miR-155 causes endothelial hyperplasia and increases microglia count and activation. The mouse model of oxygen-induced retinopathy, which recapitulates ischemia-induced aberrant neovessel growth, is characterized by increased expression of miR-155 and localized areas of microglia activation. Interestingly, miR-155 deficiency in mice reduces microglial activation, curtails abnormal vessel growth, and allows for rapid normalization of the retinal vasculature following ischemic insult. miR-155 binds to the 3'-UTR and represses the expression of the CCN1 gene, which encodes an extracellular matrix-associated integrin-binding protein that both promotes physiological angiogenesis and harnesses growth factor-induced abnormal angiogenic responses. Single CCN1 deficiency or double CCN1 and miR-155 knock-out in mice causes retinal vascular malformations typical of faulty maturation, mimicking the vascular alterations of miR-155 gain of function. During development, the miR-155/CCN1 regulatory axis balances the proangiogenic and proinflammatory activities of microglia to allow for their function as guideposts for sprout fusion and anastomosis. Under ischemic conditions, dysregulated miR-155 and CCN1 expression increases the inflammatory load and microglial activation, prompting aberrant angiogenic responses. Thus, miR-155 functions in tandem with CCN1 to modulate inflammation-induced vascular homeostasis and repair.

Eyeing the Cyr61/CTGF/NOV (CCN) group of genes in development and diseases: highlights of their structural likenesses and functional dissimilarities.

"CCN" is an acronym referring to the first letter of each of the first three members of this original group of mammalian functionally and phylogenetically distinct extracellular matrix (ECM) proteins [i.e., cysteine-rich 61 (CYR61), connective tissue growth factor (CTGF), and nephroblastoma-overexpressed (NOV)]. Although "CCN" genes are unlikely to have arisen from a common ancestral gene, their encoded proteins share multimodular structures in which most cysteine residues are strictly conserved in their positions within several structural motifs. The CCN genes can be subdivided into members developmentally indispensable for embryonic viability (e.g., CCN1, 2 and 5), each assuming unique tissue-specific functions, and members not essential for embryonic development (e.g., CCN3, 4 and 6), probably due to a balance of functional redundancy and specialization during evolution. The temporo-spatial regulation of the CCN genes and the structural information contained within the sequences of their encoded proteins reflect diversity in their context and tissue-specific functions. Genetic association studies and experimental anomalies, replicated in various animal models, have shown that altered CCN gene structure or expression is associated with "injury" stimuli--whether mechanical (e.g., trauma, shear stress) or chemical (e.g., ischemia, hyperglycemia, hyperlipidemia, inflammation). Consequently, increased organ-specific susceptibility to structural damages ensues. These data underscore the critical functions of CCN proteins in the dynamics of tissue repair and regeneration and in the compensatory responses preceding organ failure. A better understanding of the regulation and mode of action of each CCN member will be useful in developing specific gain- or loss-of-function strategies for therapeutic purposes.

Degradome products of the matricellular protein CCN1 as modulators of pathological angiogenesis in the retina.

CCN1 is a matricellular protein involved in normal vascular development and tissue repair. CCN1 exhibits cell- and context-dependent activities that are reflective of its tetramodular structure phylogenetically linked to four domains found in various matrix proteins. Here, we show that vitreal fluids from patients with proliferative diabetic retinopathy (PDR) were enriched with a two-module form of CCN1 comprising completely or partially the insulin-like growth factor-binding protein (IGFBP) and von Willebrand factor type C (vWC) domains. The two- and three-module forms comprising, in addition to IGFBP and vWC, the thrombospondin type 1 (TSP1) repeats are CCN1 degradome products by matrix metalloproteinase-2 and -14. The functional significance of CCN1 and its truncated variants was determined in the mouse model of oxygen-induced retinopathy, which simulates neovascular growth associated with PDR and assesses treatment outcomes. In this model, lentivirus-mediated expression of either CCN1 or the IGFBP-vWC-TSP1 form reduced ischemia-induced neovascularization, whereas ectopic expression of the IGFBP-vWC variant exacerbated pathological angiogenesis. The IGFBP-vWC form has potent proangiogenic properties promoting retinal endothelial cell growth, migration, and three-dimensional tubular structure formation, whereas the IGFBP-vWC-TSP1 variant suppressed cell growth and angiogenic gene expression. Both IGFBP-vWC and IGFBP-vWC-TSP1 forms exhibited predictable variations of their domain folding that enhanced their functional potential. These data provide new insights into the formation and activities of CCN1-truncated variants and raise the predictive value of the form containing completely or partially the IGFBP and vWC domains as a surrogate marker of CCN1 activity in PDR distinguishing pathological from physiological angiogenesis.

Pharmacological Activation and Transgenic Overexpression of SIRT1 Attenuate Traumatic Optic Neuropathy Induced by Blunt Head Impact.

Purpose: Resveratrol (RSV) is a nutraceutical compound known for its therapeutic potential in neurodegenerative and metabolic diseases. RSV promotes survival signals in retinal ganglion cells (RGCs) through activation of SIRT1, an NAD+-dependent deacetylase. RSV and SIRT1 reduce RGC loss induced by direct optic nerve injury, but effects in indirect models of traumatic optic neuropathy remain unknown and are examined in this study. Methods: An electromagnetic stereotaxic impactor device was used to impart five traumatic skull impacts with an inter-concussion interval of 48 hours to wild type (WT) and SIRT1 knock in (KI) C57BL/6J mice overexpressing the SIRT1 gene. A cohort of WT mice also received intranasal administration of RSV (16 mg/kg) throughout the experimental period. Loss of righting reflex (RR), optokinetic response (OKR) scores, and immunolabeled RGC count are determined to assess optic neuropathy in this model of traumatic brain injury (TBI). Results: TBI significantly decreases RGC survival and decreases OKR scores compared with control uninjured mice. Either RSV administration in WT mice, or SIRT1 overexpression in SIRT1 KI mice, significantly increases RGC survival and improves OKR scores. RR time increases after the first few impacts in all groups of mice subjected to TBI, demonstrating that RSV and SIRT1 overexpression are able to attenuate optic neuropathy following similar degrees of TBI. Conclusions: Intranasal RSV is effective in preserving visual function in WT mice following TBI. Constitutive overexpression of SIRT1 recapitulates the neuroprotective effect of RSV. Translational Relevance: Results support future exploration of RSV as a potential therapy for indirect traumatic optic neuropathy.

Comparison of SNCG and NEFH Promoter-Driven Expression of Human SIRT1 Expression in a Mouse Model of Glaucoma.

Purpose: Adeno-associated virus (AAV) demonstrates promise in delivering therapeutic genes to retinal ganglion cells (RGCs). Delivery of neuroprotective genes is constrained by packaging size and/or cell selectivity. This study compares the ability of the RGC-selective gamma-synuclein (SNCG) promoter and the smaller RGC-selective neurofilament heavy chain (NEFH) promoter, as well as portions of the RGC-selective atonal bHLH transcription factor 7 (ATOH7) enhancer, to drive gene expression in RGCs. Methods: AAV2 constructs with green fluorescent protein (GFP) or human sirtuin 1 (hSIRT1) driven by cytomegalovirus (CMV) enhancer and NEFH promoter (AAV2-eCMV-NEFH) or distal active sequences of the ATOH7 enhancer (DiATOH7) with the SNCG promoter (AAV2-DiATOH7-SNCG) were intravitreally injected into C57BL/6J mice. RGCs were immunolabeled with Brn3a antibodies and counted. AAV constructs with the utmost transduction efficiency were used to test the therapeutic efficacy of the hSIRT1 gene in 12-week-old C57BL/6J mice subjected to microbead (MB)-induced intraocular pressure (IOP) elevation. Visual function was measured using optokinetic responses (OKRs). Results: The eGFP transduction efficiency of AAV2-eCMV-NEFH was similar to that of AAV2-eCMV-SNCG and AAV2-DiATOH7-SNCG. When combined with the SNCG promoter, a larger ATOH7 enhancer was less efficient than the shorter DiATOH7 enhancer. Similarly, the hSIRT1 efficiency of AAV2-eCMV-NEFH was similar to that of AAV2-eCMV-SNCG. The latter two vectors were equally efficient in increasing RGC survival and improving visual function in the mouse model of MB-induced IOP elevation. Conclusions: SNCG and NEFH promoters represent two equally efficient and comparable RGC selective promoter sequences; however, the NEFH promoter offers a smaller packaging size. Translational Relevance: Smaller enhancer-promoter combinations can be used to deliver larger genes in human cells and for treatment in optic neuropathies including glaucoma.

Comparison of Brn3a and RBPMS Labeling to Assess Retinal Ganglion Cell Loss During Aging and in a Model of Optic Neuropathy.

Purpose: Retinal ganglion cell (RGC) loss provides the basis for diagnosis and stage determination of many optic neuropathies, and quantification of RGC survival is a critical outcome measure in models of optic neuropathy. This study examines the accuracy of manual RGC counting using two selective markers, Brn3a and RBPMS. Methods: Retinal flat mounts from 1- to 18-month-old C57BL/6 mice, and from mice after microbead (MB)-induced intraocular pressure (IOP) elevation, are immunostained with Brn3a and/or RBPMS antibodies. Four individuals masked to the experimental conditions manually counted labeled RGCs in three copies of five images, and inter- and intra-person reliability was evaluated by the intraclass correlation coefficient (ICC). Results: A larger population (approximately 10% higher) of RGCs are labeled with RBPMS than Brn3a antibody up to 6 months of age, but differences decrease to approximately 1% at older ages. Both RGC-labeled populations significantly decrease with age. MB-induced IOP elevation is associated with a significant decrease of both Brn3a- and RBPMS-positive RGCs. Notably, RGC labeling with Brn3a provides more consistent cell counts than RBPMS in interpersonal (ICC = 0.87 to 0.11, respectively) and intra-personal reliability (ICC = 0.97 to 0.66, respectively). Conclusions: Brn3a and RBPMS markers are independently capable of detecting significant decreases of RGC number with age and in response to IOP elevation despite RPBMS detecting a larger number of RGCs up to 6 months of age. Brn3a labeling is less prone to manual cell counting variability than RBPMS labeling. Overall, either marker can be used as a single marker to detect significant changes in RGC survival, each offering distinct advantages.

Connective tissue growth factor regulates retinal neovascularization through p53 protein-dependent transactivation of the matrix metalloproteinase (MMP)-2 gene.

BACKGROUND: The role of connective tissue growth factor (CTGF/CCN2) in pathological angiogenesis in the retina is unknown. RESULTS: CTGF/CCN2 stimulates retinal neovascularization through transactivation of p53 target genes such as matrix metalloproteinase (MMP)-2. CONCLUSION: CTGF/CCN2 effects on abnormal vessel formation in the retina are mediated by p53 and MMP-2. SIGNIFICANCE: CTGF/CCN2 and its downstream effectors are potential targets in the development of new antiangiogenic treatments. Pathological angiogenesis in the retina is driven by dysregulation of hypoxia-driven stimuli that coordinate physiological vessel growth. How the various components of the neovascularization signaling network are integrated to yield pathological changes has not been defined. Connective tissue growth factor (CTGF/CCN2) is an inducible matricellular protein that plays a major role in fibroproliferative disorders. Here, we show that CTGF/CCN2 was dynamically expressed in the developing murine retinal vasculature and was abnormally increased and localized within neovascular tufts in the mouse eye with oxygen-induced retinopathy. Consistent with its propitious vascular localization, ectopic expression of the CTGF/CCN2 gene further accelerated neovascularization, whereas lentivirus-mediated loss-of-function or -expression of CTGF/CCN2 harnessed ischemia-induced neovessel outgrowth in oxygen-induced retinopathy mice. The neovascular effects of CTGF/CCN2 were mediated, at least in part, through increased expression and activity of matrix metalloproteinase (MMP)-2, which drives vascular remodeling through degradation of matrix and non matrix proteins, migration and invasion of endothelial cells, and formation of new vascular patterns. In cultured cells, CTGF/CCN2 activated the MMP-2 promoter through increased expression and tethering of the p53 transcription factor to a highly conserved p53-binding sequence within the MMP-2 promoter. Concordantly, the neovascular effects of CTGF/CCN2 were suppressed by p53 inhibition that culminated in reduced enrichment of the MMP-2 promoter with p53 and decreased MMP-2 gene expression. Our data identified new gene targets and downstream effectors of CTGF/CCN2 and provided the rational basis for targeting the p53 pathway to curtail the effects of CTGF/CCN2 on neovessel formation associated with ischemic retinopathy.

CCN-Hippo YAP signaling in vision and its role in neuronal, glial and vascular cell function and behavior.

The retina is a highly specialized tissue composed of a network of neurons, glia, and vascular and epithelial cells; all working together to coordinate and transduce visual signals to the brain. The retinal extracellular matrix (ECM) shapes the structural environment in the retina but also supplies resident cells with proper chemical and mechanical signals to regulate cell function and behavior and maintain tissue homeostasis. As such, the ECM affects virtually all aspects of retina development, function and pathology. ECM-derived regulatory cues influence intracellular signaling and cell function. Reversibly, changes in intracellular signaling programs result in alteration of the ECM and downstream ECM-mediated signaling network. Our functional studies in vitro, genetic studies in mice, and multi omics analyses have provided evidence that a subset of ECM proteins referred to as cellular communication network (CCN) affects several aspects of retinal neuronal and vascular development and function. Retinal progenitor, glia and vascular cells are major sources of CCN proteins particularly CCN1 and CCN2. We found that expression of the CCN1 and CCN2 genes is dependent on the activity of YAP, the core component of the hippo-YAP signaling pathway. Central to the Hippo pathway is a conserved cascade of inhibitory kinases that regulate the activity of YAP, the final transducer of this pathway. Reversibly, YAP expression and/or activity is dependent on CCN1 and CCN2 downstream signaling, which creates a positive or negative feedforward loop driving developmental processes (e.g., neurogenesis, gliogenesis, angiogenesis, barriergenesis) and, when dysregulated, disease progression in a range of retinal neurovascular disorders. Here we describe mechanistic hints involving the CCN-Hippo-YAP regulatory axis in retina development and function. This regulatory pathway represents an opportunity for targeted therapies in neurovascular and neurodegenerative diseases. The CCN-YAP regulatory loop in development and pathology.

Report on the 11th international workshop on the CCN family of genes, Nice, October 20-24, 2022.

In celebration of the twentieth anniversary of the inception of the CCN society, and of the first post-Covid-19 live meeting, the executive board of the ICCNS had chosen Nice as the venue for the 11th International workshop on the CCN family of genes. On this occasion participation in the meeting was extended to colleagues from other cell signaling fields who were invited to present both an overview of their work and the future directions of their laboratory. Also, for the first time, the members of the JCCS Editorial Board were invited to participate in a JCCS special session during which all aspects of the journal « life ¼ were addressed and opened to free critical discussion. The scientific presentations and the discussions that followed showed once more that an expansion of the session topics was beneficial to the quality of the meeting and confirmed that the ARBIOCOM project discussed last April in Nice was now on track to be launched in 2023. The participants unanimously welcomed Professor Attramadal's proposition to organize the 2024, 12th International CCN workshop in Oslo, Norway.

Atomic Force Microscopy-Based Measurements of Retinal Microvessel Stiffness in Mice with Endothelial-Specific Deletion of CCN1.

Vascular stiffness is an independent predictor of human vascular diseases and is linked to ischemia, diabetes, high blood pressure, hyperlipidemia, and/or aging. Blood vessel stiffening increases owing to changes in the microscale architecture and/or content of extracellular, cytoskeletal, and nuclear matrix proteins. These alterations, while best appreciated in large blood vessels, also gradually occur in the microvasculature and play an important role in the initiation and progression of numerous microangiopathies including diabetic retinopathy. Although macroscopic measurements of arterial stiffness by pulse wave velocity are often used for clinical diagnosis, stiffness changes of intact microvessels and their causative factors have not been characterized. Herein, we describe the use of atomic force microscopy (AFM) to determine stiffness of mouse retinal capillaries and assess its regulation by the cellular communication network (CCN) 1, a stiffness-sensitive gene-encoded matricellular protein. AFM yields reproducible measurements of retinal capillary stiffness in lightly fixed freshly isolated retinal flat mounts. AFM measurements also show significant changes in compliance properties of the retinal microvasculature of mice with endothelial-specific deletion of CCN1, indicating that CCN1 expression, or lack thereof, affects the mechanical properties of microvascular cells in vivo. Thus, AFM has the force sensitivity and the spatial resolution necessary to measure the local modulus of retinal capillaries in situ and eventually to investigate microvascular compliance heterogeneities as key components of disease pathogenesis.

Cell-Specific Expression of Human SIRT1 by Gene Therapy Reduces Retinal Ganglion Cell Loss Induced by Elevated Intraocular Pressure.

SIRT1 prevents retinal ganglion cell (RGC) loss in several acute and subacute optic neuropathy models following pharmacologic activation or genetic overexpression. We hypothesized that adeno-associated virus (AAV)-mediated overexpression of SIRT1 in RGCs in a chronic ocular hypertension model can reduce RGC loss, thereby preserving visual function by sustained therapeutic effect. A control vector AAV-eGFP and therapeutic vector AAV-SIRT1 were constructed and optimized for transduction efficiency. A magnetic microbead mouse model of ocular hypertension was optimized to induce a time-dependent and chronic loss of visual function and RGC degeneration. Mice received intravitreal injection of control or therapeutic AAV in which a codon-optimized human SIRT1 expression is driven by a RGC selective promoter. Intraocular pressure (IOP) was measured, and visual function was examined by optokinetic response (OKR) weekly for 49 days following microbead injection. Visual function, RGC survival, and axon numbers were compared among control and therapeutic AAV-treated animals. AAV-eGFP and AAV-SIRT1 showed transduction efficiency of ~ 40%. AAV-SIRT1 maintains the transduction of SIRT1 over time and is selectively expressed in RGCs. Intravitreal injections of AAV-SIRT1 in a glaucoma model preserved visual function, increased RGC survival, and reduced axonal degeneration compared with the control construct. Over-expression of SIRT1 through AAV-mediated gene transduction indicates a RGC-selective component of neuroprotection in multiple models of acute optic nerve degeneration. Results here show a neuroprotective effect of RGC-selective gene therapy in a chronic glaucoma model characterized by sustained elevation of IOP and subsequent RGC loss. Results suggest that this strategy may be an effective therapeutic approach for treating glaucoma, and warrants evaluation for the treatment of other chronic neurodegenerative diseases.

The matricellular protein cysteine-rich protein 61 (CCN1/Cyr61) enhances physiological adaptation of retinal vessels and reduces pathological neovascularization associated with ischemic retinopathy.

Retinal vascular damages are the cardinal hallmarks of retinopathy of prematurity (ROP), a leading cause of vision impairment and blindness in childhood. Both angiogenesis and vasculogenesis are disrupted in the hyperoxia-induced vaso-obliteration phase, and recapitulated, although aberrantly, in the subsequent ischemia-induced neovessel formation phase of ROP. Yet, whereas the histopathological features of ROP are well characterized, many key modulators with a therapeutic potential remain unknown. The CCN1 protein also known as cysteine-rich protein 61 (Cyr61) is a dynamically expressed, matricellular protein required for proper angiogenesis and vasculogenesis during development. The expression of CCN1 becomes abnormally reduced during the hyperoxic and ischemic phases of ROP modeled in the mouse eye with oxygen-induced retinopathy (OIR). Lentivirus-mediated re-expression of CCN1 enhanced physiological adaptation of the retinal vasculature to hyperoxia and reduced pathological angiogenesis following ischemia. Remarkably, injection into the vitreous of OIR mice of hematopoietic stem cells (HSCs) engineered to express CCN1 harnessed ischemia-induced neovessel outgrowth without adversely affecting the physiological adaptation of retinal vessels to hyperoxia. In vitro exposure of HSCs to recombinant CCN1 induced integrin-dependent cell adhesion, migration, and expression of specific endothelial cell markers as well as many components of the Wnt signaling pathway including Wnt ligands, their receptors, inhibitors, and downstream targets. CCN1-induced Wnt signaling mediated, at least in part, adhesion and endothelial differentiation of cultured HSCs, and inhibition of Wnt signaling interfered with normalization of the retinal vasculature induced by CCN1-primed HSCs in OIR mice. These newly identified functions of CCN1 suggest its possible therapeutic utility in ischemic retinopathy.

Role of Erythropoietin Receptor Signaling in Macrophages or Choroidal Endothelial Cells in Choroidal Neovascularization.

Erythropoietin (EPO) has been proposed to reduce the progression of atrophic age-related macular degeneration (AMD) due to its potential role in neuroprotection. However, overactive EPO receptor (EPOR) signaling increased laser-induced choroidal neovascularization (CNV) and choroidal macrophage number in non-lasered mice, which raised the question of whether EPOR signaling increased CNV through the recruitment of macrophages to the choroid that released pro-angiogenic factors or through direct angiogenic effects on endothelial cells. In this study, we addressed the hypothesis that EPOR signaling increased CNV by direct effects on macrophages or endothelial cells. We used tamoxifen-inducible macrophage-specific or endothelial cell-specific EPOR knockout mice in the laser-induced CNV model, and cultured choroidal endothelial cells isolated from adult human donors. We found that macrophage-specific knockout of EPOR influenced laser-induced CNV in females only, whereas endothelial-specific knockout of EPOR reduced laser-induced CNV in male mice only. In cultured human choroidal endothelial cells, knockdown of EPOR reduced EPO-induced signal transducer and activator of transcription 3 (STAT3) activation. Taken together, our findings suggest that EPOR signaling in macrophages or choroidal endothelial cells regulates the development of CNV in a sex-dependent manner. Further studies regarding the role of EPO-induced signaling are required to assess EPO safety and to select or develop appropriate therapeutic approaches.