Gut Microbiota-Immune System Interactions during Acute Kidney Injury

Kidney double positive T cells have distinct characteristics in normal and diseased kidneys

Multiple types of T cells have been described and assigned pathophysiologic functions in the kidneys. However, the existence and functions of TCR+CD4+CD8+ (double positive; DP) T cells are understudied in normal and diseased murine and human kidneys. We studied kidney DPT cells in mice at baseline and after ischemia reperfusion (IR) and cisplatin injury. Additionally, effects of viral infection and gut microbiota were studied. Human kidneys from patients with renal cell carcinoma were evaluated. Our results demonstrate that DPT cells expressing CD4 and CD8 co-receptors constitute a minor T cell population in mouse kidneys. DPT cells had significant Ki67 and PD1 expression, effector/central memory phenotype, proinflammatory cytokine (IFNγ, TNFα and IL-17) and metabolic marker (GLUT1, HKII, CPT1a and pS6) expression at baseline. IR, cisplatin and viral infection elevated DPT cell proportions, and induced distinct functional and metabolic changes. scRNA-seq analysis showed increased expression of Klf2 and Ccr7 and enrichment of TNFα and oxidative phosphorylation related genes in DPT cells. DPT cells constituted a minor population in both normal and cancer portion of human kidneys. In conclusion, DPT cells constitute a small population of mouse and human kidney T cells with distinct inflammatory and metabolic profile at baseline and following kidney injury.

Microbiome modulation after severe acute kidney injury accelerates functional recovery and decreases kidney fibrosis

Targeting gut microbiota has shown promise to prevent experimental acute kidney injury (AKI). However, this has not been studied in relation to accelerating recovery and preventing fibrosis. Here, we found that modifying gut microbiota with an antibiotic administered after severe ischemic kidney injury in mice, particularly with amoxicillin, accelerated recovery. These indices of recovery included increased glomerular filtration rate, diminution of kidney fibrosis, and reduction of kidney profibrotic gene expression. Amoxicillin was found to increase stool Alistipes, Odoribacter and Stomatobaculum species while significantly depleting Holdemanella and Anaeroplasma. Specifically, amoxicillin treatment reduced kidney CD4+T cells, interleukin (IL)-17 +CD4+T cells, and tumor necrosis factor-α double negative T cells while it increased CD8+T cells and PD1+CD8+T cells. Amoxicillin also increased gut lamina propria CD4+T cells while decreasing CD8+T and IL-17+CD4+T cells. Amoxicillin did not accelerate repair in germ-free or CD8-deficient mice, demonstrating microbiome and CD8+T lymphocytes dependence for amoxicillin protective effects. However, amoxicillin remained effective in CD4-deficient mice. Fecal microbiota transplantation from amoxicillin-treated to germ-free mice reduced kidney fibrosis and increased Foxp3+CD8+T cells. Amoxicillin pre-treatment protected mice against kidney bilateral ischemia reperfusion injury but not cisplatin-induced AKI. Thus, modification of gut bacteria with amoxicillin after severe ischemic AKI is a promising novel therapeutic approach to accelerate recovery of kidney function and mitigate the progression of AKI to chronic kidney disease.

Acute kidney injury and distant organ dysfunction-network system analysis

Acute kidney injury (AKI) occurs in about half of critically ill patients and associates with high in-hospital mortality, increased long-term mortality post-discharge and subsequent progression to chronic kidney disease. Numerous clinical studies have shown that AKI is often complicated by dysfunction of distant organs, which is a cause of the high mortality associated with AKI. Experimental studies have elucidated many mechanisms of AKI-induced distant organ injury, which include inflammatory cytokines, oxidative stress and immune responses. This review will provide an update on evidence of organ crosstalk and potential therapeutics for AKI-induced organ injuries, and present the new concept of a systemic organ network to balance homeostasis and inflammation that goes beyond kidney-crosstalk with a single distant organ.

Overview of the Medical Management of the Critically Ill Patient

The medical management of the critically ill patient focuses predominantly on treatment of the underlying condition (e g, sepsis or respiratory failure). However, in the past decade, the importance of initiating early prophylactic treatment for complications arising from care in the intensive care unit setting has become increasingly apparent. As survival from critical illness has improved, there is an increased prevalence of postintensive care syndrome-defined as a decline in physical, cognitive, or psychologic function among survivors of critical illness. The Intensive Care Unit Liberation Bundle, a major initiative of the Society of Critical Care Medicine, is centered on facilitating the return to normal function as early as possible, with the intent of minimizing iatrogenic harm during necessary critical care. These concepts are universally applicable to patients seen by nephrologists in the intensive care unit and may have particular relevance for patients with kidney failure either on dialysis or after kidney transplant. In this article, we will briefly summarize some known organ-based consequences associated with critical illness, review the components of the ABCDEF bundle (the conceptual framework for Intensive Care Unit Liberation), highlight the role nephrologists can play in implementing and complying with the ABCDEF bundle, and briefly discuss areas for additional research.

Intestinal Microbiota in Experimental Acute Kidney Injury

Recent studies have demonstrated an important role played by gut microbiota in maintaining intestinal homeostasis and host immune system function. Gut microbiota have been studied in experimental acute kidney injury (AKI) using different mice and rat models exposed to either ischemia or cisplatin-mediated tubular injury. Differences in inflammatory markers and severity of AKI have been observed between germ-free mice, wild-type mice, and mice treated with antibiotics or specific bacteria. Interventions modifying the gut microbiota after experimental AKI have had either beneficial or harmful effects on kidney tubular injury and recovery. These findings provide strong evidence for a modulatory role of gut microbiota during AKI. Ischemic and cis-platin-induced AKI have distinct stool microbial signatures based on 16s sequencing. Future in-depth studies exploring the mechanisms of how the microbiota influence AKI and development of feasible therapeutic options have the potential to improve outcomes in clinical AKI.

Role of T cells in ischemic acute kidney injury and repair

Ischemic acute kidney injury (AKI) is a common medical problem with significant mortality and morbidity, affecting a large number of patients globally. Ischemic AKI is associated with intrarenal inflammation as well as systemic inflammation; thus, the innate and adaptive immune systems are implicated in the pathogenesis of ischemic AKI. Among various intrarenal immune cells, T cells play major roles in the injury process and in the repair mechanism affecting AKI to chronic kidney disease transition. Importantly, T cells also participate in distant organ crosstalk during AKI, which affects the overall outcomes. Therefore, targeting T cell-mediated pathways and T cell-based therapies have therapeutic promise for ischemic AKI. Here, we review the major populations of kidney T cells and their roles in ischemic AKI.