Cx3cr1 controls kidney resident macrophage heterogeneity.

Kidney macrophages are comprised of both monocyte-derived and tissue resident populations; however, the heterogeneity of kidney macrophages and factors that regulate their heterogeneity are poorly understood. Herein, we performed single cell RNA sequencing (scRNAseq), fate mapping, and parabiosis to define the cellular heterogeneity of kidney macrophages in healthy mice. Our data indicate that healthy mouse kidneys contain four major subsets of monocytes and two major subsets of kidney resident macrophages (KRM) including a population with enriched Ccr2 expression, suggesting monocyte origin. Surprisingly, fate mapping data using the newly developed Ms4a3Cre Rosa Stopf/f TdT model indicate that less than 50% of Ccr2+ KRM are derived from Ly6chi monocytes. Instead, we find that Ccr2 expression in KRM reflects their spatial distribution as this cell population is almost exclusively found in the kidney cortex. We also identified Cx3cr1 as a gene that governs cortex specific accumulation of Ccr2+ KRM and show that loss of Ccr2+ KRM reduces the severity of cystic kidney disease in a mouse model where cysts are mainly localized to the kidney cortex. Collectively, our data indicate that Cx3cr1 regulates KRM heterogeneity and niche-specific disease progression.

A Comprehensive Immune Cell Atlas of Cystic Kidney Disease Reveals the Involvement of Adaptive Immune Cells in Injury-Mediated Cyst Progression in Mice.

BACKGROUND: Inducible disruption of cilia-related genes in adult mice results in slowly progressive cystic disease, which can be greatly accelerated by renal injury. METHODS: To identify in an unbiased manner modifier cells that may be influencing the differential rate of cyst growth in injured versus non-injured cilia mutant kidneys at a time of similar cyst severity, we generated a single-cell atlas of cystic kidney disease. We conducted RNA-seq on 79,355 cells from control mice and adult-induced conditional Ift88 mice (hereafter referred to as cilia mutant mice) that were harvested approximately 7 months post-induction or 8 weeks post 30-minute unilateral ischemia reperfusion injury. RESULTS: Analyses of single-cell RNA-seq data of CD45+ immune cells revealed that adaptive immune cells differed more in cluster composition, cell proportion, and gene expression than cells of myeloid origin when comparing cystic models with one another and with non-cystic controls. Surprisingly, genetic deletion of adaptive immune cells significantly reduced injury-accelerated cystic disease but had no effect on cyst growth in non-injured cilia mutant mice, independent of the rate of cyst growth or underlying genetic mutation. Using NicheNet, we identified a list of candidate cell types and ligands that were enriched in injured cilia mutant mice compared with aged cilia mutant mice and non-cystic controls that may be responsible for the observed dependence on adaptive immune cells during injury-accelerated cystic disease. CONCLUSIONS: Collectively, these data highlight the diversity of immune cell involvement in cystic kidney disease.

Early infiltrating macrophage subtype correlates with late-stage phenotypic outcome in a mouse model of hepatorenal fibrocystic disease.

Hepatorenal fibrocystic disease (HRFCD) is a genetically inherited disorder related to primary cilia dysfunction in which patients display varying levels of fibrosis, bile duct expansion, and inflammation. In mouse models of HRFCD, the phenotype is greatly impacted by the genetic background in which the mutation is placed. Macrophages are a common factor associated with progression of HRFCD and are also strongly influenced by the genetic background. These data led us to hypothesize that macrophage subtypes that change in relation to the genetic background are responsible for the variable phenotypic outcomes in HRFCD. To test this hypothesis, we utilized a mouse model of HRFCD (Ift88Orpk mice) on the C57BL/6 and BALB/c inbred backgrounds that have well-documented differences in macrophage subtypes. Our analyses of infiltrating macrophage subtypes confirm that genetic strain influences the subtype of infiltrating macrophage present during normal postnatal liver development and in Ift88Orpk livers (Ly6clo in C57BL/6 vs Ly6chi in BALB/c). Each infiltrating macrophage subtype was similarly associated with a unique phenotypic outcome as analysis of liver tissue shows that C57BL/6 Ift88Orpk mice have increased bile duct expansion, but reduced levels of fibrosis compared to BALB/c Ift88Orpk livers. RNA sequencing data suggest that the ability to infiltrate macrophage subtypes to influence the phenotypic outcome may be due to unique ligand-receptor signaling between infiltrating macrophages and cilia dysfunctional biliary epithelium. To evaluate whether specific macrophage subtypes cause the observed phenotypic divergence, we analyzed the liver phenotype in BALB/c Ift88Orpk mice on a CCR2-/- background. Unexpectedly, the loss of Ly6chi macrophages, which were strongly enriched in BALB/c Ift88Orpk mice, did not significantly alter liver fibrosis. These data indicate that macrophage subtypes may correlate with HRFCD phenotypic outcome, but do not directly cause the pathology.

Deletion of a 19-Amino-Acid Region in Clostridioides difficile TcdB2 Results in Spontaneous Autoprocessing and Reduced Cell Binding and Provides a Nontoxic Immunogen for Vaccination.

Clostridioides difficile toxin B (TcdB) is an intracellular toxin responsible for many of the pathologies of C. difficile infection. The two variant forms of TcdB (TcdB1 and TcdB2) share 92% sequence identity but have reported differences in rates of cell entry, autoprocessing, and overall toxicity. This 2,366-amino-acid, multidomain bacterial toxin glucosylates and inactivates small GTPases in the cytosol of target cells, ultimately leading to cell death. Successful cell entry and intoxication by TcdB are known to involve various conformational changes in the protein, including a proteolytic autoprocessing event. Previous studies found that amino acids 1753 to 1852 influence the conformational states of the proximal carboxy-terminal domain of TcdB and could contribute to differences between TcdB1 and TcdB2. In the current study, a combination of approaches was used to identify sequences within the region from amino acids 1753 to 1852 that influence the conformational integrity and cytotoxicity of TcdB2. Four deletion mutants with reduced cytotoxicity were identified, while one mutant, TcdB2Δ1769-1787, exhibited no detectable cytotoxicity. TcdB2Δ1769-1787 underwent spontaneous autoprocessing and was unable to interact with CHO-K1 or HeLa cells, suggesting a potential change in the conformation of the mutant protein. Despite the putative alteration in structural stability, vaccination with TcdB2Δ1769-1787 induced a TcdB2-neutralizing antibody response and protected against C. difficile disease in a mouse model. These findings indicate that the 19-amino-acid region spanning residues 1769 to 1787 in TcdB2 is crucial to cytotoxicity and the structural regulation of autoprocessing and that TcdB2Δ1769-1787 is a promising candidate for vaccination.

Intrinsic Toxin-Derived Peptides Destabilize and Inactivate Clostridium difficile TcdB.

Clostridium difficile infection (CDI) is a major cause of hospital-associated, antibiotic-induced diarrhea, which is largely mediated by the production of two large multidomain clostridial toxins, TcdA and TcdB. Both toxins coordinate the action of specific domains to bind receptors, enter cells, and deliver a catalytic fragment into the cytosol. This results in GTPase inactivation, actin disassembly, and cytotoxicity. TcdB in particular has been shown to encode a region covering amino acids 1753 to 1851 that affects epitope exposure and cytotoxicity. Surprisingly, studies here show that several peptides derived from this region, which share the consensus sequence 1769NVFKGNTISDK1779, protect cells from the action of TcdB. One peptide, PepB2, forms multiple interactions with the carboxy-terminal region of TcdB, destabilizes TcdB structure, and disrupts cell binding. We further show that these effects require PepB2 to form a higher-order polymeric complex, a process that requires the central GN amino acid pair. These data suggest that TcdB1769-1779 interacts with repeat sequences in the proximal carboxy-terminal domain of TcdB (i.e., the CROP domain) to alter the conformation of TcdB. Furthermore, these studies provide insights into TcdB structure and functions that can be exploited to inactivate this critical virulence factor and ameliorate the course of CDI.IMPORTANCEClostridium difficile is a leading cause of hospital-associated illness that is often associated with antibiotic treatment. To cause disease, C. difficile secretes toxins, including TcdB, which is a multidomain intracellular bacterial toxin that undergoes conformational changes during cellular intoxication. This study describes the development of peptide-based inhibitors that target a region of TcdB thought to be critical for structural integrity of the toxin. The results show that peptides derived from a structurally important region of TcdB can be used to destabilize the toxin and prevent cellular intoxication. Importantly, this work provides a novel means of toxin inhibition that could in the future develop into a C. difficile treatment.

T-cell stimulating protein A (TspA) of Neisseria meningitidis is required for optimal adhesion to human cells.

T-cell stimulating protein A (TspA) is an immunogenic, T-cell and B-cell stimulating protein of Neisseria meningitidis. Sequence similarity between TspA and FimV, a Pseudomonas aeruginosa protein involved in twitching motility, suggested a link between TspA and type IV pili (Tfp). To determine the role of TspA an isogenic deletion mutant was created. Loss of TspA did not affect twitching motility or piliation indicating that there are functional differences between TspA and FimV. Mutation of tspA led to a significant reduction in adhesion of meningococci to meningothelial and HEp-2 cells, which was not due to a lack of transcription of adjacent genes or pilC1. Other Tfp-mediated phenotypes (i.e. auto-aggregation and transformation competence) were not altered. Our results indicate that the role of TspA in adhesion is unlikely to be directly linked to the function of Tfp. TspA was expressed by all N. meningitidis and Neisseria polysaccharea strains examined but not by Neisseria gonorrhoeae or Neisseria lactamica, although sequences with homology to tspA were present in their genomes. In summary, TspA is a highly conserved antigen that is required for optimal adhesion of meningococci to human cells.