Tamm-Horsfall protein (THP), also known as uromodulin, is a kidney-specific protein produced by cells of the thick ascending limb of the loop of Henle. Although predominantly secreted apically into the urine, where it becomes highly polymerized, THP is also released basolaterally, toward the interstitium and circulation, to inhibit tubular inflammatory signaling. Whether, through this latter route, THP can also regulate the function of renal interstitial mononuclear phagocytes (MPCs) remains unclear, however. Here, we show that THP is primarily in a monomeric form in human serum. Compared with wild-type mice, THP mice had markedly fewer MPCs in the kidney. A nonpolymerizing, truncated form of THP stimulated the proliferation of human macrophage cells in culture and partially restored the number of kidney MPCs when administered to THP mice. Furthermore, resident renal MPCs had impaired phagocytic activity in the absence of THP. After ischemia-reperfusion injury, THP mice, compared with wild-type mice, exhibited aggravated injury and an impaired transition of renal macrophages toward an M2 healing phenotype. However, treatment of THP mice with truncated THP after ischemia-reperfusion injury mitigated the worsening of AKI. Taken together, our data suggest that interstitial THP positively regulates mononuclear phagocyte number, plasticity, and phagocytic activity. In addition to the effect of THP on the epithelium and granulopoiesis, this new immunomodulatory role could explain the protection conferred by THP during AKI.

Single cell sequencing studies have characterized the transcriptomic signature of cell types within the kidney. However, the spatial distribution of acute kidney injury (AKI) is regional and affects cells heterogeneously. We first optimized coordination of spatial transcriptomics and single nuclear sequencing datasets, mapping 30 dominant cell types to a human nephrectomy. The predicted cell type spots corresponded with the underlying histopathology. To study the implications of AKI on transcript expression, we then characterized the spatial transcriptomic signature of two murine AKI models: ischemia reperfusion injury (IRI) and cecal ligation puncture (CLP). Localized regions of reduced overall expression were associated with injury pathways. Using single cell sequencing, we deconvoluted the signature of each spatial transcriptomic spot, identifying patterns of colocalization between immune and epithelial cells. Neutrophils infiltrated the renal medulla in the ischemia model. Atf3 was identified as a chemotactic factor in S3 proximal tubules. In the CLP model, infiltrating macrophages dominated the outer cortical signature and Mdk was identified as a corresponding chemotactic factor. The regional distribution of these immune cells was validated with multiplexed CO-Detection by inDEXing (CODEX) immunofluorescence. Spatial transcriptomic sequencing complements single cell sequencing by uncovering mechanisms driving immune cell infiltration and detection of relevant cell subpopulations.

Sepsis is a dynamic state that progresses at variable rates and has life-threatening consequences. Staging patients along the sepsis timeline requires a thorough knowledge of the evolution of cellular and molecular events at the tissue level. Here, we investigated the kidney, an organ central to the pathophysiology of sepsis. Single-cell RNA-sequencing in a murine endotoxemia model revealed the involvement of various cell populations to be temporally organized and highly orchestrated. Endothelial and stromal cells were the first responders. At later time points, epithelial cells upregulated immune-related pathways while concomitantly downregulating physiological functions such as solute homeostasis. Sixteen hours after endotoxin, there was global cell–cell communication failure and organ shutdown. Despite this apparent organ paralysis, upstream regulatory analysis showed significant activity in pathways involved in healing and recovery. This rigorous spatial and temporal definition of murine endotoxemia will uncover precise biomarkers and targets that can help stage and treat human sepsis.

Hydrogen peroxide (HO) increases paracellular permeability of Madin-Darby canine kidney (MDCK) cells, but the mechanism mediating this effect remains unclear. Treatment of MDCK cells with HO activated ERK 1/2. Inhibition of ERK 1/2 activation blocked the ability of HO to increase paracellular permeability. Knockdown of zonula occludens-1 (ZO-1) protein but not occludin eliminated the ability of HO to increase paracellular permeability. HO treatment did not, however, affect the total cell content or contents of the Triton X-100-soluble and -insoluble fractions for occludin, ZO-1, or ZO-2. HO treatment decreased the number of F-actin stress fibers in the basal portion of the cells. Similar to wild-type MDCK cells, HO increased ERK 1/2 activation in ZO-1 knockdown and occludin knockdown cells. Inhibition of ERK 1/2 activation blocked the increase in paracellular permeability in occludin knockdown cells. ZO-1 knockdown cell paracellular permeability was regulated by PP1, an src inhibitor, indicating that the loss of response to HO was not a general loss of the ability to regulate the paracellular barrier. Inhibition of myosin ATPase activity with blebbistatin increased paracellular permeability in ZO-1 knockdown cells but not in wild-type MDCK cells. HO treatment sensitized wild-type MDCK cells to inhibition of myosin ATPase. Knockdown of TOCA-1 protein, which promotes formation of local branched actin networks, reproduced the effects of ZO-1 protein knockdown. These results demonstrate that HO increases MDCK cell paracellular permeability through activation of ERK 1/2. This HO action requires ZO-1 protein and TOCA-1 protein, suggesting involvement of the actin cytoskeleton.

The ability of hydrogen peroxide (H2O2) to increase paracellular permeability of renal epithelial cell monolayers was examined and the role of occludin in this regulation was investigated. H2O2 treatment increased the paracellular movement of calcein, a marker for the leak pathway permeability, across monolayers of two renal epithelial cell lines, MDCK and LLC-PK1, in a concentration-dependent manner. At the same concentrations, H2O2 did not alter transepithelial resistance (TER) nor increase cell death. The magnitude of the H2O2-induced increase in leak pathway permeability was inversely related to cellular occludin protein content. H2O2 treatment did not produce any major change in total cellular content or Triton X-100-soluble or –insoluble fraction content of occludin protein. Occludin protein staining at the tight junction region was diminished following H2O2 treatment. The most dramatic effect of H2O2 was on the dynamic mobility of GFP-occludin into the tight junction region. H2O2 treatment slowed lateral movement of GFP-occludin into the tight junction region but not on the apical membrane. Further, removal of the cytoplasmic C-terminal region of occludin protein eliminated the effect of H2O2 on GFP-occludin lateral movement into the tight junction region. An increase in the mobile fraction of GFP-occludin was associated with a loss of response to H2O2. These data indicate that the H2O2-induced increase in renal epithelial cell paracellular permeability is mediated, at least in part, through occludin protein, possibly through a slowing of the rate of occludin movement into the tight junction region.

15Clinical sepsis is a highly dynamic state that progresses at variable rates and has life-16 threatening consequences. Staging patients along the sepsis timeline requires a thorough 17 knowledge of the evolution of cellular and molecular events at the tissue level. Here, we 18 investigated the kidney, an organ central to the pathophysiology of sepsis. Single cell RNA 19 sequencing revealed the involvement of various cell populations in injury and repair to be 20 temporally organized and highly orchestrated. We identified key changes in gene expression 21 that altered cellular functions and can explain features of clinical sepsis. These changes 22 converged towards a remarkable global cell-cell communication failure and organ shutdown at a 23 well-defined point in the sepsis timeline. Importantly, this time point was also a transition 24 towards the emergence of recovery pathways. This rigorous spatial and temporal definition of 25 murine sepsis will uncover precise biomarkers and targets that can help stage and treat human 26 sepsis. 27 28 associated UMAP positions from the merged Seurat object, as well as the principal component 340 table. This generated an RNA velocity Fig. mapped using the merged Seurat object cell 341 positions. Similar analysis was done for the immune subsetted data.342 Cell-cell communication analysis 343We applied the Cellphone database 41 of known receptor-ligand pairs to assess cell-cell 344 communication in our integrated dataset. Gene expression data from the integrated Seurat file

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Difficult behavior exhibited by dialysis patients is a spectrum that includes nonadherence, verbal or physical abuse, and threatening acts. Such behaviors may lead to harmful consequences to the patient, other patients, the facility, and staff and can culminate in involuntary discharge. It is important to recognize that these “difficult behaviors” may be due to underlying psychosocial or medical issues, which places an onus on care providers to explore further. According to the Conditions for Coverage (CfC) for dialysis facilities, it falls upon the medical director to coordinate and oversee policies for patient satisfaction, patient safety and rights, involuntary discharges, and adverse events and outcomes. Thus, medical directors are liable for their own actions, and their staff for which they have oversight, for harm or perceived harm to patients in response to difficult behaviors. Guidelines to deal with specific patient behavior scenarios have been published by the Decreasing Dialysis Patient Conflict National Task Force of the Forum of end-stage renal disease (ESRD) Networks. The common denominator for these difficult scenarios is impaired communication, and the majority of patient concerns involve issues with staff, policies, treatments, and diet. Involuntary discharge of a patient should always be viewed as a last resort, and there is a structured process described in the CfC that requires the involvement of the respective ESRD Network and the facility medical director. As physicians, we are bound by ethical and growing legal obligations to act in an appropriate, ethical, and fair manner to patients who are considered to be “difficult.”