Maria B. Grant

Diabetic retinopathy (DR) is a leading cause of vision loss and is associated with reduced nuclear retinoid X receptor (RXR) activity. Retinal explants exposed to high glucose showed downregulation of RXR, peroxisome proliferator–activated receptor (PPAR), and liver X receptor-β and their lipid metabolism targets (Abca1, Scd1, and Acox1). Supplementation with the RXR agonist UAB126 restored nuclear receptor signaling and preferentially activated RXR/PPAR heterodimers. We evaluated UAB126 microparticles (UAB126-MP), a sustained-release RXR agonist formulation, for pharmacokinetic, molecular, and functional effects in db/db mouse retinas. A single intravitreal injection of UAB126-MP provided extended drug exposure for up to 6 months and increased retinal RXRα expression. Functionally, UAB126-MP preserved scotopic and photopic electroretinographic responses at 2 months and sustained cone photoreceptor function at 6 months. However, it did not reduce acellular capillaries. At 6 months, immunostaining and flow cytometry revealed decreased retinal macrophage/microglial infiltration and reduced CD45-positive myeloid cells and monocytes. These findings indicate that RXR agonism supports neuronal protection and immune modulation but does not prevent vasodegeneration, suggesting primarily neuroprotective and anti-inflammatory actions. Collectively, UAB126-MP confers durable retinal protection through nuclear receptor–mediated pathways, underscoring its potential as a long-acting therapeutic strategy for DR. Article Highlights: High glucose exposure of retinal explants reduces expression of nuclear receptors retinoid X receptor (RXR), peroxisome proliferator–activated receptor, and liver X receptor-β, and treatment with UAB126 increases the formation of RXR-peroxisome proliferator–activated receptor heterodimers. Sustained release of UAB126-loaded microparticles enables intravitreal drug delivery for up to 6 months. Intravitreal UAB126 microparticles injection in diabetic mice confers long-term neuroprotection and anti-inflammatory benefits. RXR-targeted therapy represents a promising approach strategy for managing diabetic retinopathy.

Aberrant monocyte/macrophage activation in diabetes drives chronic inflammation and diabetic complications. Although epigenetic mechanisms are implicated in these processes, the contribution of three-dimensional (3D) chromatin reorganization remains unclear. Here, we use integrated multi-omics approaches to profile gene expression, chromatin accessibility and 3D chromatin architecture in human CD14⁺ monocyte-derived macrophages exposed to high glucose and TNF-α (HT), mimicking the diabetic milieu. HT induces inflammatory transcription programs that recapitulate those observed in diabetes and dynamically remodel chromatin accessibility, enhancer-promoter interactions, and topologically associated domains. Inflammatory genes exhibit increased chromatin accessibility, whereas cell cycle and metabolic genes display reduced accessibility and weakened enhancer-promoter interactions. These architectural changes promote the convergence of lineage-determining and signal-dependent transcription factors at enhancer-promoter loops, generating distinct regulatory hubs that orchestrate pro-inflammatory responses. Similar enhancer-promoter interactions are observed in peripheral blood derived monocytes from individuals with diabetes. Furthermore, perturbing chromatin interactions via CRISPR interference targeting HT-induced enhancers suppresses nearby CCL2 and other chemokine genes. Collectively, this first comprehensive enhancer connectome map of macrophages under diabetic conditions advances the field by revealing extensive disease-associated rewiring of the 3D epigenome, highlighting chromatin architecture and epigenetic mechanisms as potential therapeutic target for diabetes-associated inflammation. Graphical In diabetes, high glucose (Glc) and inflammatory cytokines remodel macrophage 3D chromatin architecture and enhancer connectomes, altering enhancer-promoter interactions, facilitating the convergence of lineage-specific and signal-dependent transcription factors (such as NF-κB) that regulate inflammatory factors associated with macrophage activation. This can promote chronic inflammation and accelerate diabetic complications. Targeted enhancer editing strategies could enable new epigenetic therapies to mitigate chronic inflammatory diabetes complications.

Using micro‐computed tomography, we identified a network of skull channels in the calvarium of type 2 diabetic (T2D) mice that remained structurally intact and numerically stable despite long‐standing disease. The retention of calvaria bone marrow structural integrity was associated with preserved hematopoietic capacity under chronic diabetic conditions, which was not observed in the bone marrow of long bones. A distinctive feature of the calvarial bone marrow compartment was its direct exposure to cerebrospinal fluid (CSF), a property not shared by tibial bone marrow. To characterize the biochemical environment of the murine calvarium, we profiled oxysterols in CSF using mass spectrometry. The CSF exhibited elevated levels of neurotrophic and anti‐inflammatory oxysterols, including 22‐hydroxycholesterol (22‐OHC) and 27‐hydroxycholesterol (27‐OHC). To assess whether this protective oxysterol signature was conserved in humans, we analyzed CSF samples from diabetic and non‐diabetic individuals with obesity‐associated idiopathic intracranial hypertension (IIH). Human CSF contained 7α‐hydroxy‐3‐oxo‐4‐cholestenoic acid (7‐HOCA), a metabolite of 27‐OHC, supporting the conservation of this neuroprotective profile across species. Given the anatomical proximity of the calvarium to the eye, we hypothesized that calvaria bone marrow may serve as a reservoir for immune cells recruited to the injured or infected retina. The calvaria bone marrow was the predominant source of myeloid angiogenic cells (MACs) and neutrophils, mobilizing these cells at levels approximately 20‐fold higher than long bones. These findings demonstrate that calvarial bone marrow plays a critical role in retinal immune defense, while maintaining both structural integrity and functional capacity despite chronic T2D.

Diabetes mellitus (DM) is a debilitating chronic disorder that results in ocular microvascular complications, including diabetic retinopathy (DR) and diabetic macular edema (DME). Early detection and timely intervention for DR and DME are crucial for improving visual outcomes in affected patients. Ophthalmic imaging plays a vital role in the screening, diagnosis, and management of DR and DME. In this review, a comprehensive overview of the imaging modalities frequently utilized in the assessment of DR and DME, encompassing both structural and functional imaging techniques are presented. The key imaging findings that are associated with the various stages of DR and DME are underscored and their diagnostic utility in assessing disease progression and visual function are evaluated. Additionally, we discuss emerging imaging biomarkers that are currently under investigation, which hold significant potential for improving the diagnostic and prognostic capabilities of imaging for DR and DME patients. Finally, the advent of new imaging methods, such as ultrawide-field imaging (UWFI) and deep learning models, which have markedly improved the detection of retinal pathologies are considered.

Background: Both host and microbe metabolism of tryptophan (Trp) is altered in diabetes; however, the molecular mechanisms are incompletely understood. Objective: We used strategies to increase either angiotensin converting enzyme-2 (ACE-2) dependent or independent Trp absorption in a model of type 2 diabetes, db/db mice, and tested whether the strategies could prevent development of diabetic retinopathy (DR), the most common microvascular complication of diabetes. Additionally, we investigated levels of Trp metabolites in humans with and without DR. Design: Enhanced ACE-2 dependent Trp absorption was achieved with gavage of genetically modified bacteria that preserved intestinal ACE2:sodium coupled neutral amino acid transporter expression. ACE-2 independent Trp absorption was achieved by gavage of the Trp dipeptide (Isoleucine-Trp; IW) absorbed via solute carrier family 15 member 1. Both strategies were used either as a prevention (6 months treatment) or intervention (3 months treatment) and at the conclusion, intestinal, metabolic and retinal studies were performed including spatial mass spectroscopy (MS). Plasma Trp metabolites and gut permeability markers were measured in individuals with T2D with (n=30) and without (n=40) DR and compared with healthy controls (n=35). Results: Lactobacillus paracasei -ACE2 or IW treatment prevented DR, corrected dysbiosis, enriched Trp-metabolising bacteria, improved gut barrier integrity, boosted incretin secretion and restored glucose homeostasis in db/db mice. Spatial MS identified indole propionic acid (IPA) as a metabolite in the retinal pigment epithelial layer protecting the posterior blood retinal barrier. T2D individuals with DR demonstrated elevated serum markers of endotoxemia and intestinal barrier disruption while showing reduced levels of the beneficial metabolite IPA and elevated levels of the toxic metabolite indole sulfate. Conclusion: Nutraceutical strategies that restore Trp metabolism or IPA serve as both a biomarker and a treatment for DR.

Purpose: We previously reported that the systemic administration of preprogrammed mouse hematopoietic bone marrow-derived progenitor cells (HSPCs) improved visual function and restored a functional retinal pigment epithelial (RPE) layer. Here, we investigated the potential impact of donor vs. host age on systemic cellular therapy in a murine model of retinal degeneration. Methods: HSPCs from young (8 weeks) and old (15 months) mice were programmed ex vivo with a lentiviral vector expressing the RPE65 gene (LV-RPE65) and systemically administering into young or old SOD2 KD mice. Visual loss and pathological changes were evaluated by electroretinogram (ERG), optical coherence tomography (OCT), histology, and immunohistochemistry. Results: Old donor HSPCs administered to old manganese superoxide dismutase (SOD2) knockdown (KD) recipient mice offered the least benefit. This was exemplified by the reduced recruitment and incorporation of LV-RPE65 HSPC into the RPE layer, as well as decreased improvement in visual function, retinal thinning, and limited reduction in oxidative damage and microglial activation. LV-RPE65 HSPC from young mice incorporated into the RPE layer of old SOD2 KD mice, though to a lesser extent than young cells administered to young hosts, offered some level of protection. By contrast, LV-RPE65 HSPCs from old mice, located to the subretinal space of young host mice, reduced visual loss, although some retinal pathology was observed. Conclusions: The administration of LV-RPE65 HSPC from old donors to old SOD2 KD mice offered the least improvement. Translational Relevance: Our findings highlight how both donor and recipient age impact the success of HSPC-based retinal therapy and using cells from aged donors for AMD treatment may have some limitations.

Purpose: To investigate the therapeutic potential of inducible pluripotent stem cell (hiPSC)-based vascular repair, we evaluated two vascular reparative cell populations, CD34⁺ cells derived from hiPSC (hiPSC-CD34⁺) and endothelial colony forming cells (ECFCs) derived from hiPSC (iPS-ECFCs), alone and in combination, in a type 2 diabetic (db/db) mouse model of DR. Methods: hiPSC-CD34⁺ cells (1 × 10⁴) or iPSC- ECFCs (1 × 10⁵) alone or in combination (1.1 × 10⁵) were injected into the vitreous of immunosuppressed db/db mice with six months of established diabetes. One month post-injection, mice underwent electroretinography (ERG) and optical coherence tomography (OCT) to evaluate functional and structural retinal recovery with iPSC administration. Immunohistochemistry (IHC) was used to assess recruitment and incorporation of cells into the retinal vasculature. Retinas from the experimental groups were analyzed using Functional Proteomics via Reverse Phase Protein Array (RPPA). Results: Functional assessment via ERG demonstrated significant improvements in retinal response in the diabetic cohorts treated with either hiPSC-derived CD34⁺ cells or hiPSC-ECFCs. Retinal thickness, assessed by OCT, was restored to near-nondiabetic levels in mice treated with hiPSC-CD34⁺ cells alone and the combination group, whereas hiPSC-ECFCs alone did not significantly affect retinal thickness. One month following intravitreal injection, hiPSC-CD34⁺ cells were localized to perivascular regions, whereas hiPSC-ECFCs were observed to integrate directly into the retinal vasculature. RPPA analysis revealed interaction-significant changes, and this was interpreted as a combination-specific, non-additive host responses (m⁶A, PI3K–AKT–mTOR, glycolysis, endothelial junction pathways). Conclusions: The studies support that injection of hiPSC-CD34⁺ cells and hiPSC-ECFCs, both individually and in combination, showed benefit; however, iPSC combination-specific effects were identified by measurement of retinal thickness and by RPPA.

Therapeutic plasma exchange (TPE) is a blood purification technique which functions to remove pathological plasma constituents such as autoantibodies, inflammatory cytokines, immune complexes, and extracellular vesicles (EVs) that contribute to a range of disease states. In this review, we examine current and emerging indications for TPE across cardiovascular, metabolic, neurological, inflammatory, and oncological diseases. We cover emerging preclinical animal models and new applications, emphasizing the roles of cellular signaling and EV biology in mediating plasma functions, and discuss unique therapeutic “windows of opportunity” offered by TPE. We conclude that TPE is underutilized in both preventative and precision medicine, and that next generation TPE therapies will involve personalized plasma biomarker and modulation feedback, with synergistic plasma infusion therapies to mitigate age associated disease and promote tissue rejuvenation.

This study investigated the therapeutic potential of the nuclear retinoid X receptor (RXR) in mitigating the progression of alpha-synucleinopathies (αSNPs), particularly in Parkinson’s disease (PD). PD-like pathology in mice was successfully induced through the co-delivery of AAV expressing human α-synuclein (αS) and αS preformed fibrils (PFFs) into the substantia nigra pars compacta (SNpc). Significant increases in Lewy body (LB)-like inclusions, loss of tyrosine hydroxylase-positive (TH+) neurons, and reductions in dopamine (DA) levels in the striatum were observed. Additionally, diminished levels of PPARα and NURR1—proteins essential for neuronal survival—along with elevated expression of IBA1 and GFAP, markers of microglial activation and astrocytic gliosis, respectively, are associated with the pathogenesis of Parkinson’s disease. AAV-mediated overexpression of human RXRα demonstrated preservation of TH+ neurons, prevention of DA decline, and attenuation of αS accumulation. Furthermore, RXR-treated PD brains showed a reduced number of GFAP+ and Iba1+ cells, decreased GFAP+ and IBA1+ immunoreactivity, and fewer and less widespread LB-like aggregates. RXR overexpression also enhanced the production of PPARα and NURR1. These findings suggest that RXRα upregulation promotes neuroprotection by mitigating αSNPs and chronic neuroinflammation, a major contributor to PD progression. This research underscores the therapeutic potential of targeting nuclear receptors, such as RXR, in neurodegenerative diseases like PD.