Jonathan G. Crowston’s research while affiliated with Duke-NUS Medical School and other places

Age and elevated intraocular pressure (IOP) are the two major risk factors for developing glaucoma, a leading cause of blindness worldwide that is characterized by the loss of retinal ganglion cells (RGCs). Although vision loss is irreversible over the long term, accumulating evidence points to short‐term improvement of vision in glaucoma patients in response to certain interventions, suggesting that RGCs have the capacity to recover function. In the present study, we sought to investigate the mechanisms underlying loss and recovery of RGC function in response to aging and IOP injury, with a focus on synaptic connectivity. Using electroretinography, we found that advancing age was associated with a substantial reduction in function across all retinal layers in the absence of significant cell loss. A superimposed injury induced by IOP elevation led to the selective loss of RGC function in young and middle‐aged mice that was associated with a decrease in paired excitatory synapses. RGC functional recovery after injury was significantly delayed in middle‐aged mice and was mediated through different cellular mechanisms than in young mice. Whereas young mice regained excitatory synaptic inputs from bipolar cells, functional recovery in older mice was instead mediated through an increase in intrinsic RGC excitability, associated with modulation of the action potential threshold and axon initial segment length. Our findings provide new insights into the impact of advancing age on RGC resilience to IOP injury. Boosting the capacity for RGC recovery by reversing the effect of advancing age offers a new therapeutic approach for glaucoma management.

SIGNIFICANCE Previous evidence showed that transient receptor potential vanilloid 4 (TRPV4) inhibition was protective of retinal ganglion cell (RGC) loss after chronic intraocular pressure (IOP) elevation in young animals. However, the role of TRPV4 in mechanosensing IOP changes in the aging eye is not well understood. PURPOSE This study compared the recovery of retinal function and structure after acute IOP elevation in 3- and 12-month-old mouse eyes with and without TRPV4 inhibition. METHODS We examined retinal TRPV4 expression in 2-month-old rodent eyes using immunohistochemistry and transcript analysis of isolated macroglia and RGCs. To modulate TRPV4, mice were treated daily with either vehicle or a TRPV4 antagonist (HC-067047 10 mg/kg) delivered intraperitoneally for 7 days before and 7 days after IOP elevation (50 mmHg for 30 minutes). Retinal function and structure were assessed using dark-adapted full-field electroretinography and optical coherence tomography, respectively. RESULTS We showed that Müller cells strongly expressed TRPV4. Seven days after IOP elevation, RGC functional recovery was significantly poorer in older mice treated with TRPV4 antagonist compared with age-matched vehicle controls (−54 ± 7% vs. −24 ± 10%, p=0.046) and their younger TRPV4 antagonist–treated counterparts (−5 ± 5%, p<0.001). CONCLUSIONS This study showed that there was an age-related deficit in RGC functional recovery from IOP elevation with TRPV4 inhibition.

There is a growing need to better characterise senescent cells in the CNS and retina. The recently published SenMayo gene panel was developed to identify transcriptomic signatures of senescence across multiple organ systems, but the retina was not included. While other approaches have identified senescent signatures in the retina, these have largely focused on experimental models in young animals. We therefore conducted a detailed single-cell RNA-seq analysis to identify senescent cell populations in the retina of different aged mice and compared these with five comprehensive human and mouse retina and brain transcriptome datasets. Transcriptomic signatures of senescence were most apparent in mouse and human retinal glial cells, with IL4, 13 and 10 and the AP1 pathway being the most prominent markers involved. Similar levels of transcriptional senescence were observed in the retinal glia of young and old mice, whereas the human retina showed significantly increased enrichment scores with advancing age.

Sarcopenia is the age-related degeneration of skeletal muscle, resulting in loss of skeletal muscle tone, mass, and quality. Skeletal muscle is a source of systemic metabolites and macromolecules important for neuronal health, function and healthy neuronal aging. Age-related loss of skeletal muscle might result in decreased metabolite and macromolecule availability, resulting in reduced neuronal function or increased susceptibility to unhealthy aging and neurodegenerative diseases. We aimed to identify muscle metabolite candidates that regulate healthy aging. C57BL/6J mice were aged to young adult (4 months) and old age (25 months) and skeletal muscle was collected. Age related muscle loss was confirmed by reduced muscle mass, muscle fiber degeneration, reduced myosin intensity, in addition to a metabolic shift and increased DNA damage in skeletal muscle. Using a low molecular weight enriched metabolomics protocol, we assessed the metabolic profile of skeletal muscle from young adult and old mice and identified 20 metabolites that were significantly changed in aged muscle. These candidate metabolites were tested in C. elegans assays of lifespan, health span, muscle-, and mitochondrial morphology under normal and stressed conditions. We identified four candidate metabolites (beta-alanine, 4-guanidinobutanoic acid, 4-hydroxyproline, pantothenic acid) that when supplemented in C. elegans provided robust gero- and mitochondrial protection. These candidates also affected life-, and health span in C. elegans models of amyotrophic lateral sclerosis and Duchenne muscular dystrophy. Our findings support that aging muscle can be used to identify novel metabolite modulators of lifespan and health and may show promise for future treatments of neurodegenerative and neuromuscular disorders.

Prècis Mean IOP, complete and overall success, mean IOP-lowering medications, incidence of hypertensive phase and complications were found to be comparable between patients undergoing Ahmed Glaucoma Valve implantation (AGVI) with adjunctive bevacizumab versus AGVI alone. Purpose This meta-analysis aims to assess how adjunctive bevacizumab impacts the surgical outcomes of Ahmed glaucoma valve implantation (AGVI) compared to AGVI alone in all subtypes of refractory glaucoma. Methods A systematic search of databases for relevant randomised controlled trials (RCTs) was performed in March 2023. Primary outcomes included mean intraocular pressure (IOP) and success rates. Secondary outcomes were mean IOP-lowering medications, incidence of hypertensive phase, and complications. Qualitative assessment, meta-analysis, subgroup analyses, and sensitivity analysis were performed. Results Five RCTs comprising 203 eyes were included in the quantitative analysis. Initial meta-analysis showed a strong yet non-significant trend (all P >0.05) favouring adjunctive bevacizumab in all outcomes of interest. Significant heterogeneity was observed for mean IOP and success outcomes at all timepoints (all I ² >50%). Subgroup analysis of administration route revealed a reduced incidence of hyphaema in the intravitreal bevacizumab (IVB) subgroup (OR, 0.10; 95% CI, 0.02–0.59; P =0.01) with significant heterogeneity persisting in the IVB subgroup for all measures (all I ² >50%). Post hoc sensitivity analysis of studies without concurrent PRP for mean IOP and success outcomes demonstrated more conservative effect sizes with a corresponding decrease in heterogeneity for all measures (all I ² <30%). Conclusion Published studies investigating the role of adjunctive bevacizumab show a strong trend to improved outcomes but contain a relatively small number of participants. This analysis underpins the need for an adequately powered RCT to explore the role of anti-VEGF agents in AGVI surgery.

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system’s limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium’s efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.