Farnesoid X receptor prevents neutrophil extracellular traps via reduced sphingosine-1-phosphate in chronic kidney disease

Mas Signaling Potentiates Neutropil Extracellular Traps Formation Induced by Endothelial Cells Derived S1P in Mice with Acute Liver Failure

Mas, a newly identified G-protein-coupled receptor, is prevalent in myeloid-derived immune cells and plays a key role in inflammation. This study investigates Mas signaling and neutrophil extracellular traps (NETs) in acute liver failure (ALF), aiming to elucidate their mechanisms. Male Mas1-/- and wild-type mice, aged 6-8 weeks, receive intraperitoneally injected with lipopolysaccharide (LPS)/D-galactosamine (D-Gal) (L/G) to study NETs formation. Hepatic Mas expression increases in WT-L/G mice, whereas systemic Mas1 knockout significantly reduces L/G-induced NETs and hepatotoxicity. Antibiotics treatment and co-housing (Mas1-/--L/G and WT-L/G mice) experiments show that gut flora influences the disease phenotype in Mas1-/--L/G mice. Fecal metabolite analysis suggests that mice may be protected by reduced deoxycholic acid (DCA) production in Mas1-/- activated hepatic farnesoid X receptor (FXR), suppressing sphingosine-1-phosphate (S1P)-dependent NETs. Additionally, Mas1-/- also activates the FXR-S1P-NETs axis in the liver by inhibiting SHP2. Single-cell sequencing shows decreased interaction between endothelial cells and Cldn1+CD177+ senescent neutrophils through Col4a1-CD44. This inhibits S1P-induced Raf signaling pathway activation and NETs formation. Mas signaling significantly impacts NETs formation, highlighting its potential as an anti-inflammatory therapeutic target for ALF.

NAD+ prevents chronic kidney disease by activating renal tubular metabolism

Chronic kidney disease (CKD) is associated with renal metabolic disturbances, including impaired fatty acid oxidation (FAO). Nicotinamide adenine dinucleotide (NAD+) is a small molecule that participates in hundreds of metabolism-related reactions. NAD+ levels are decreased in CKD, and NAD+ supplementation is protective. However, both the mechanism of how NAD+ supplementation protects from CKD, as well as the cell types involved, are poorly understood. Using a mouse model of Alport syndrome, we show that nicotinamide riboside (NR), an NAD+ precursor, stimulated renal PPARα signaling and restored FAO in the proximal tubules, thereby protecting from CKD in both sexes. Bulk RNA-sequencing showed that renal metabolic pathways were impaired in Alport mice and activated by NR in both sexes. These transcriptional changes were confirmed by orthogonal imaging techniques and biochemical assays. Single-nuclei RNA sequencing and spatial transcriptomics, both the first of their kind to our knowledge from Alport mice, showed that NAD+ supplementation restored FAO in proximal tubule cells. Finally, we also report, for the first time to our knowledge, sex differences at the transcriptional level in this Alport model. In summary, the data herein identify a nephroprotective mechanism of NAD+ supplementation in CKD, and they demonstrate that this benefit localizes to the proximal tubule cells.

Characterization of the Ocular Phenotype in a Col4a3 Knockout Mouse Model of Alport Syndrome

Purpose

Alport syndrome (AS) is a genetic condition caused by a dysfunctional collagen (IV) α3α4α5 heterotrimer, leading to basement membrane instability and, ultimately, abnormalities in the kidney, inner ear, and eyes. This study aimed to characterize ocular pathology of AS by focusing on inflammatory and fibrotic markers.

Methods

Col4a3tm1Dec knockout (KO) mice eyes were evaluated for the localization of collagen (IV) α3 and collagen (IV) α4, then stained for transforming growth factor-β1 (TGF-β1), TGF-β2, connective tissue growth factor (CTGF), and β-catenin. mRNA levels of the profibrotic genes S100a4, Acta2, Col1a1, Snai1, Snai2, and Twist1 were assessed using real-time reverse transcription quantitative PCR (RT-qPCR).

Results

Collagen (IV) α3 and collagen (IV) α4 were co-expressed in Descemet's and Bruch's membrane but not in the retina, lens, or other corneal substructures. Immunofluorescence quantitation revealed upregulation of TGF-β1 in the anterior lens and TGF-β2 in the retina of KO eyes. Conversely, CTGF and β-catenin were shown to be elevated in the corneal epithelium but not the retina or lens. RT-qPCR showed an increase in the transcription of Acta2, Col1a1, and Snai2 in the retinas and Snai2 in anterior segments of KO mice.

Conclusions

Col4a3 KO mice exhibited a differential inflammatory and profibrotic response in the cornea, retina, and lens, which may play a role in the ocular pathology of AS.

NAD + activates renal metabolism and protects from chronic kidney disease in a model of Alport syndrome

Chronic kidney disease (CKD) is associated with renal metabolic disturbances, including impaired fatty acid oxidation (FAO). Nicotinamide adenine dinucleotide (NAD + ) is a small molecule that participates in hundreds of metabolism-related reactions. NAD + levels are decreased in CKD, and NAD + supplementation is protective. However, both the mechanism of how NAD + supplementation protects from CKD, as well as the cell types involved, are poorly understood. Using a mouse model of Alport syndrome, we show that nicotinamide riboside (NR), an NAD + precursor, stimulates renal peroxisome proliferator-activated receptor alpha signaling and restores FAO in the proximal tubules, thereby protecting from CKD in both sexes. Bulk RNA-sequencing shows that renal metabolic pathways are impaired in Alport mice and activated by NR in both sexes. These transcriptional changes are confirmed by orthogonal imaging techniques and biochemical assays. Single nuclei RNA-sequencing and spatial transcriptomics, both the first of their kind from Alport mice, show that NAD + supplementation restores FAO in proximal tubule cells. Finally, we also report, for the first time, sex differences at the transcriptional level in this Alport model. In summary, we identify a nephroprotective mechanism of NAD + supplementation in CKD, and we demonstrate that the proximal tubule cells substantially contribute to this benefit.

Neutrophils-biology and diversity

Neutrophils, the most abundant white blood cells in the human circulation, play crucial roles in various diseases, including kidney disease. Traditionally viewed as short-lived pro-inflammatory phagocytes that release reactive oxygen species, cytokines and neutrophil extracellular traps, recent studies have revealed their complexity and heterogeneity, thereby challenging this perception. Neutrophils are now recognized as transcriptionally active cells capable of proliferation and reverse migration, displaying phenotypic and functional heterogeneity. They respond to a wide range of signals and deploy various cargo to influence the activity of other cells in the circulation and in tissues. They can regulate the behavior of multiple immune cell types, exhibit innate immune memory, and contribute to both acute and chronic inflammatory responses while also promoting inflammation resolution in a context-dependent manner. Here, we explore the origin and heterogeneity of neutrophils, their functional diversity, and the cues that regulate their effector functions. We also examine their emerging role in infectious and non-infectious diseases with a particular emphasis on kidney disease. Understanding the complex behavior of neutrophils during tissue injury and inflammation may provide novel insights, thereby paving the way for potential therapeutic strategies to manage acute and chronic conditions. By deciphering their multifaceted role, targeted interventions can be developed to address the intricacies of neutrophil-mediated immune responses and improve disease outcomes.