Molecular regulation of retinal regeneration is context specific

Many genes are known to regulate retinal regeneration following widespread tissue damage. Conversely, genes controlling regeneration following limited retinal cell loss, akin to disease conditions, are undefined. Combining a novel retinal ganglion cell (RGC) ablation-based glaucoma model, single cell omics, and rapid CRISPR/Cas9-based knockout methods to screen 100 genes, we identified 18 effectors of RGC regeneration kinetics. Surprisingly, 32 of 33 previously known/implicated regulators of retinal tissue regeneration were not required for RGC replacement; 7 knockouts accelerated regeneration, including sox2, olig2, and ascl1a . Mechanistic analyses revealed loss of ascl1a increased "fate bias", the propensity of progenitors to produce RGCs. These data demonstrate plasticity and context-specificity in how genes function to control regeneration, insights that could help to advance disease-tailored therapeutics for replacing lost retinal cells.

One sentence summary

We discovered eighteen genes that regulate the regeneration of retinal ganglion cells in zebrafish.

Transcriptomic comparison of two selective retinal cell ablation paradigms in zebrafish reveals shared and cell-specific regenerative responses

Retinal Müller glia (MG) can act as stem-like cells to generate new neurons in both zebrafish and mice. In zebrafish, retinal regeneration is innate and robust, resulting in the replacement of lost neurons and restoration of visual function. In mice, exogenous stimulation of MG is required to reveal a dormant and, to date, limited regenerative capacity. Zebrafish studies have been key in revealing factors that promote regenerative responses in the mammalian eye. Increased understanding of how the regenerative potential of MG is regulated in zebrafish may therefore aid efforts to promote retinal repair therapeutically. Developmental signaling pathways are known to coordinate regeneration following widespread retinal cell loss. In contrast, less is known about how regeneration is regulated in the context of retinal degenerative disease, i.e., following the loss of specific retinal cell types. To address this knowledge gap, we compared transcriptomic responses underlying regeneration following targeted loss of rod photoreceptors or bipolar cells. In total, 2,531 differentially expressed genes (DEGs) were identified, with the majority being paradigm specific, including during early MG activation phases, suggesting the nature of the injury/cell loss informs the regenerative process from initiation onward. For example, early modulation of Notch signaling was implicated in the rod but not bipolar cell ablation paradigm and components of JAK/STAT signaling were implicated in both paradigms. To examine candidate gene roles in rod cell regeneration, including several immune-related factors, CRISPR/Cas9 was used to create G0 mutant larvae (i.e., "crispants"). Rod cell regeneration was inhibited in stat3 crispants, while mutating stat5a/b, c7b and txn accelerated rod regeneration kinetics. These data support emerging evidence that discrete responses follow from selective retinal cell loss and that the immune system plays a key role in regulating "fate-biased" regenerative processes.

Nanoparticle-based targeting of microglia improves the neural regeneration enhancing effects of immunosuppression in the zebrafish retina

Retinal Müller glia function as injury-induced stem-like cells in zebrafish but not mammals. However, insights gleaned from zebrafish have been applied to stimulate nascent regenerative responses in the mammalian retina. For instance, microglia/macrophages regulate Müller glia stem cell activity in the chick, zebrafish, and mouse. We previously showed that post-injury immunosuppression by the glucocorticoid dexamethasone accelerated retinal regeneration kinetics in zebrafish. Similarly, microglia ablation enhances regenerative outcomes in the mouse retina. Targeted immunomodulation of microglia reactivity may therefore enhance the regenerative potential of Müller glia for therapeutic purposes. Here, we investigated potential mechanisms by which post-injury dexamethasone accelerates retinal regeneration kinetics, and the effects of dendrimer-based targeting of dexamethasone to reactive microglia. Intravital time-lapse imaging revealed that post-injury dexamethasone inhibited microglia reactivity. The dendrimer-conjugated formulation: (1) decreased dexamethasone-associated systemic toxicity, (2) targeted dexamethasone to reactive microglia, and (3) improved the regeneration enhancing effects of immunosuppression by increasing stem/progenitor proliferation rates. Lastly, we show that the gene rnf2 is required for the enhanced regeneration effect of D-Dex. These data support the use of dendrimer-based targeting of reactive immune cells to reduce toxicity and enhance the regeneration promoting effects of immunosuppressants in the retina.

NTR 2.0: a rationally engineered prodrug-converting enzyme with substantially enhanced efficacy for targeted cell ablation

Transgenic expression of bacterial nitroreductase (NTR) enzymes sensitizes eukaryotic cells to prodrugs such as metronidazole (MTZ), enabling selective cell-ablation paradigms that have expanded studies of cell function and regeneration in vertebrates. However, first-generation NTRs required confoundingly toxic prodrug treatments to achieve effective cell ablation, and some cell types have proven resistant. Here we used rational engineering and cross-species screening to develop an NTR variant, NTR 2.0, which exhibits ~100-fold improvement in MTZ-mediated cell-specific ablation efficacy, eliminating the need for near-toxic prodrug treatment regimens. NTR 2.0 therefore enables sustained cell-loss paradigms and ablation of previously resistant cell types. These properties permit enhanced interrogations of cell function, extended challenges to the regenerative capacities of discrete stem cell niches, and novel modeling of chronic degenerative diseases. Accordingly, we have created a series of bipartite transgenic reporter/effector resources to facilitate dissemination of NTR 2.0 to the research community.

Unusual cause of glomerular deposition disease: Collagenofibrotic glomerulopathy

Collagenofibrotic glomerulopathy is a rare condition characterized by deposition of Type III collagen fibers in the subendothelial space and mesangium of the glomerulus. Only 17 cases have been reported from India. A definite diagnosis can only be established when typical histological findings are supported by electron microscopy. It is characterized by indolent progression and has no definitive therapy.

Saprochaete capitata fungal infection in renal transplant recipient

Saprochaete capitata is a fungus that rarely causes human infections; majority of infections were reported in patients with hematological malignancies. Here, we report a case of Saprochaete capitata infection in a renal transplant recipient. To the best of our knowledge, this is the first case report of infection with this unusual organism in renal transplant recipients. In our patient, this organism was isolated from broncho alveolar lavage, and it responded dramatically to the combination of amphotericin and voriconazole.

Prostate-specific membrane antigen as a target for cancer imaging and therapy

The prostate-specific membrane antigen (PSMA) is a molecular target whose use has resulted in some of the most productive work toward imaging and treating prostate cancer over the past two decades. A wide variety of imaging agents extending from intact antibodies to low-molecular-weight compounds permeate the literature. In parallel there is a rapidly expanding pool of antibody-drug conjugates, radiopharmaceutical therapeutics, small-molecule drug conjugates, theranostics and nanomedicines targeting PSMA. Such productivity is motivated by the abundant expression of PSMA on the surface of prostate cancer cells and within the neovasculature of other solid tumors, with limited expression in most normal tissues. Animating the field is a variety of small-molecule scaffolds upon which the radionuclides, drugs, MR-detectable species and nanoparticles can be placed with relative ease. Among those, the urea-based agents have been most extensively leveraged, with expanding clinical use for detection and more recently for radiopharmaceutical therapy of prostate cancer, with surprisingly little toxicity. PSMA imaging of other cancers is also appearing in the clinical literature, and may overtake FDG for certain indications. Targeting PSMA may provide a viable alternative or first-line approach to managing prostate and other cancers.

Expression pattern of BMPs during chick limb development

In vertebrates, BMPs (bone morphogenic proteins) play critical roles in establishing the basic embryonic body plan and are involved in the development of a large variety of organs and tissues. Here, we analyzed the expression pattern of various BMPs (2, 4, 5 and 7) by whole mount in situ hybridization during chick limb development. In limb, expression of BMPs suggests evolutionary conserved mechanisms of BMP-dependent differentiation between lower and higher vertebrates. During the early developmental stages, BMP-2 and BMP-7 are expressed in the posterior distal mesenchyme leaving a less prominent expression anteriorly. BMP-4 is initially expressed in the anterior mesenchyme and spreads later to the whole mesenchyme leaving a stronger expression at the anterior side. From HH-stage 25, expression of BMP-4 is observed in the anterior-posterior margins of the limb bud. The BMPs 2, 4 and 7 are expressed strongly in the AER, whereas BMP-5 is expressed as a weak signal in the distal mesoderm during the early stages of limb development. Later from HH-stage 25 onwards, BMP-5 is expressed in the dorsal and ventral muscular mass of the developing limb. As digits become identifiable, expression of BMPs are observed in the interdigital mesenchyme and can also be detected along the contours of the developing phalanges and at the distal tips of the digits. All these BMPs are found to be expressed in the developing feather buds from day 8 onwards.

Expression pattern of VEGFR-2 (Quek1) during quail development

The growth and maintenance of the blood and lymphatic vascular systems is to a large extent controlled by members of the vascular endothelial growth factor (VEGF) family via the tyrosine kinase receptors (VEGFRs) expressed in angioblastic cells. Here, we analyzed the Quek1 (VEGFR-2) expression pattern by whole mount in situ hybridization during quail development. During early embryogenesis, Quek1 expression was detected at the caudal end of the blastoderm and primitive streak and in the head paraxial mesoderm. In somites, expression was observed from HH-stage 9 onwards in the dorsolateral region of both the forming and recently formed somites. During somite maturation, expression persists in the lateral portion of the somitic compartments, the dermomyotome and the sclerotome. Additionally, a second expression domain in the maturing somite was observed in the medial part of the sclerotome adjacent to the neural tube. This expression domain extended medially and dorsally and surrounded the neural tube during later stages. In the notochord, expression was observed from HH-stage 23 onwards. In the limb bud, expression was initiated in the mesenchyme at HH-stage 17. During organogenesis, expression was detected in the pharyngeal arches and in the anlagen of the esophagus, trachea, stomach, lungs, liver, heart and gut. Expression was also seen in feather buds from day 7 onwards. Our results confirm the angiogenic potential of the mesoderm and suggest that VEGFR-2 expressing cells represent multiple pools of mesodermal precursors of the hematopoietic and angiopoietic lineages.

Effects of glucocorticoids on lymphocyte activation in patients with steroid-sensitive and steroid-resistant asthma

BACKGROUND

Glucocorticoids are important medications used to control the airway inflammation associated with asthma. Synthetic glucocorticoids vary in their binding affinity for the glucocorticoid receptor (GCR).

METHODS

We compared hydrocortisone, beclomethasone dipropionate, triamcinolone acetonide, flunisolide, and budesonide with regard to their capacity to inhibit phytohemagglutinin-induced peripheral blood mononuclear cell proliferation from six patients with steroid-sensitive asthma and seven patients with steroid-resistant asthma. Peripheral blood mononuclear cell GCR binding affinities for dexamethasone and budesonide were also determined for both patient groups by using a radioligand binding assay and Scatchard analysis.

RESULTS

Dose-dependent inhibition was demonstrated for all glucocorticoids in both patient groups, with the steroid-resistant group requiring approximately 2 log-fold more glucocorticoids for an equivalent degree of inhibition. The mean concentrations necessary to cause 50% inhibition of lymphocyte proliferation (IC50s) for the steroid-sensitive group ranged from 2 x 10(-10) mol/L for budesonide to 7 x 10(-8) mol/L for hydrocortisone, whereas the mean IC50s for the steroid-resistant group ranged from approximately 2 x 10(-8) mol/L for budesonide to greater than 10(-6) mol/L for hydrocortisone. In addition, a significant correlation was noted between the degree of inhibition of lymphocyte proliferation (IC50) and the binding affinity of dexamethasone to the GCR. Patients with steroid-resistant asthma have been shown to have a reduced GCR binding affinity. The GCR binding affinity for budesonide was significantly higher in both groups (i.e., lower dissociation constant) than that obtained for dexamethasone.

CONCLUSION

These data suggest that glucocorticoids such as budesonide, by virtue of their high GCR binding affinities and greater ability to suppress lymphocyte proliferation, may therefore be beneficial in the management of difficult-to-control asthma.

Reduced glucocorticoid binding affinity in asthma is related to ongoing allergic inflammation

Recent studies indicate that chronic asthma is associated with a spectrum of glucocorticoid receptor (GCR) binding abnormalities that are cytokine-inducible. These GCR abnormalities may contribute to poor asthma control and failure to respond to glucocorticoid (GC) therapy. The purpose of this study was to determine whether GCR defects are associated with poorly controlled asthma, and whether diminished GCR binding is reversible following a course of GC therapy. We enrolled 12 patients with poorly controlled asthma characterized by nocturnal awakening with cough or wheezing, AM FEV1 < 70%, or FEV1 variability of > 25% requiring a short course of high dose GC therapy. GCR binding affinity was measured in peripheral blood mononuclear cells using a radioligand binding assay before and after the GC course. Spirometry, serum cortisol, eosinophil cationic protein (ECP), and soluble IL-2 receptor (sIL-2R) levels were also performed before and after the GC course. At baseline, all subjects had airflow obstruction that significantly improved (median FEV1 increased from 65.0% to 89.5% of predicted, median FEV1/FVC ratio increased from 0.60 to 0.72) with therapy. A diminished GCR binding affinity at baseline was noted with an elevated median dissociation constant (Kd) of 29.0 nM (interquartile range at the 25th and 75th percentile [IQ] of 22.3 and 44.5 nM) compared with normal controls (Kd 8.0 nM [IQ 7.0, 9.2]). Following the GC course, a significant decrease in the Kd was seen. Serum ECP and sIL-2R levels at baseline were elevated, with serum ECP demonstrating a significant reduction following the GC course.(ABSTRACT TRUNCATED AT 250 WORDS)