Stress resilience-enhancing drugs preserve tissue structure and function in degenerating retina via phosphodiesterase inhibition

Chronic, progressive retinal diseases, such as age-related macular degeneration (AMD), diabetic retinopathy, and retinitis pigmentosa, arise from genetic and environmental perturbations of cellular and tissue homeostasis. These disruptions accumulate with repeated exposures to stress over time, leading to progressive visual impairment and, in many cases, legal blindness. Despite decades of research, therapeutic options for the millions of patients suffering from these disorders remain severely limited, especially for treating earlier stages of pathogenesis when the opportunity to preserve the retinal structure and visual function is greatest. To address this urgent, unmet medical need, we employed a systems pharmacology platform for therapeutic development. Through integrative single-cell transcriptomics, proteomics, and phosphoproteomics, we identified universal molecular mechanisms across distinct models of age-related and inherited retinal degenerations, characterized by impaired physiological resilience to stress. Here, we report that selective, targeted pharmacological inhibition of cyclic nucleotide phosphodiesterases (PDEs), which serve as critical regulatory nodes that modulate intracellular second messenger signaling pathways, stabilized the transcriptome, proteome, and phosphoproteome through downstream activation of protective mechanisms coupled with synergistic inhibition of degenerative processes. This therapeutic intervention enhanced resilience to acute and chronic forms of stress in the degenerating retina, thus preserving tissue structure and function across various models of age-related and inherited retinal disease. Taken together, these findings exemplify a systems pharmacology approach to drug discovery and development, revealing a new class of therapeutics with potential clinical utility in the treatment or prevention of the most common causes of blindness.

Elucidation of a dynamic interplay between a beta-2 adrenergic receptor, its agonist, and stimulatory G protein

G protein-coupled receptors (GPCRs) represent the largest group of membrane receptors for transmembrane signal transduction. Ligand-induced activation of GPCRs triggers G protein activation followed by various signaling cascades. Understanding the structural and energetic determinants of ligand binding to GPCRs and GPCRs to G proteins is crucial to the design of pharmacological treatments targeting specific conformations of these proteins to precisely control their signaling properties. In this study, we focused on interactions of a prototypical GPCR, beta-2 adrenergic receptor (β2AR), with its endogenous agonist, norepinephrine (NE), and the stimulatory G protein (Gs). Using molecular dynamics (MD) simulations, we demonstrated the stabilization of cationic NE, NE(+), binding to β2AR by Gs protein recruitment, in line with experimental observations. We also captured the partial dissociation of the ligand from β2AR and the conformational interconversions of Gs between closed and open conformations in the NE(+)-β2AR-Gs ternary complex while it is still bound to the receptor. The variation of NE(+) binding poses was found to alter Gs α subunit (Gsα) conformational transitions. Our simulations showed that the interdomain movement and the stacking of Gsα α1 and α5 helices are significant for increasing the distance between the Gsα and β2AR, which may indicate a partial dissociation of Gsα The distance increase commences when Gsα is predominantly in an open state and can be triggered by the intracellular loop 3 (ICL3) of β2AR interacting with Gsα, causing conformational changes of the α5 helix. Our results help explain molecular mechanisms of ligand and GPCR-mediated modulation of G protein activation.

Role of coagulation in persistent renal ischemia following reperfusion in an animal model

Ischemic acute kidney injury is common, deadly, and accelerates the progression of chronic kidney disease, yet has no specific therapy. After ischemia, reperfusion is patchy with early and persistent impairment in regional renal blood flow and cellular injury. We tested the hypothesis that intrarenal coagulation results in sustained renal ischemia following reperfusion, using a well-characterized model. Markedly decreased, but heterogeneous, microvascular plasma flow with microthrombi was found postischemia by intravital microscopy. Widespread tissue factor expression and fibrin deposition were also apparent. Clotting was accompanied by complement activation and inflammation. Treatment with exosomes derived from renal tubular cells or with the fibrinolytic urokinase, given 24 h postischemia when renal failure was established, significantly improved microvascular flow, coagulation, serum creatinine, and histological evidence of injury. These data support the hypothesis that intrarenal clotting occurs early and the resultant sustained ischemia is a critical determinant of renal failure following ischemia; they demonstrate that the coagulation abnormalities are amenable to therapy and that therapy results in improvement in both function and postischemic inflammation.NEW & NOTEWORTHY Ischemic renal injury carries very high morbidity and mortality, yet has no specific therapy. We found markedly decreased, heterogeneous microvascular plasma flow, tissue factor induction, fibrin deposition, and microthrombi after renal ischemia-reperfusion using a well-characterized model. Renal exosomes or the fibrinolytic urokinase, administered after renal failure was established, improved microvascular flow, coagulation, renal function, and histology. Data demonstrate that intrarenal clotting results in sustained ischemia amenable to therapy that improves both function and postischemic inflammation.

Loss of vascular endothelial glutaminase inhibits tumor growth and metastasis, and increases sensitivity to chemotherapy

Glutamine is the most abundant non-essential amino acid in blood stream; yet it's concentration in tumor interstitium is markedly lower than that in the serum, reflecting the huge demand of various cell types in tumor microenvironment for glutamine. While many studies have investigated glutamine metabolism in tumor epithelium and infiltrating immune cells, the role of glutamine metabolism in tumor blood vessels remains unknown. Here, we report that inducible genetic deletion of glutaminase (GLS) specifically in host endothelium, GLSECKO, impairs tumor growth and metastatic dissemination in vivo. Loss of GLS decreased tumor microvascular density, increased perivascular support cell coverage, improved perfusion, and reduced hypoxia in mammary tumors. Importantly, chemotherapeutic drug delivery and therapeutic efficacy were improved in tumor-bearing GLSECKO hosts or in combination with GLS inhibitor, CB839. Mechanistically, loss of GLS in tumor endothelium resulted in decreased leptin levels, and exogenous recombinant leptin rescued tumor growth defects in GLSECKO mice. Together, these data demonstrate that inhibition of endothelial glutamine metabolism normalizes tumor vessels, reducing tumor growth and metastatic spread, improving perfusion, and reducing hypoxia, and enhancing chemotherapeutic delivery. Thus, targeting glutamine metabolism in host vasculature may improve clinical outcome in patients with solid tumors.