Search

Background Inflammation is a key driver of the transition of acute kidney injury to progressive fibrosis and chronic kidney disease (AKI-to-CKD transition). Blocking a-disintegrin-and-metalloprotease-17 (ADAM17)-dependent ectodomain shedding, in particular of epidermal growth factor receptor (EGFR) ligands and of the type 1 inflammatory cytokine tumor necrosis factor (TNF), reduces pro-inflammatory and pro-fibrotic responses after ischemic AKI or unilateral ureteral obstruction (UUO), a classical fibrosis model. Metalloprotease or EGFR inhibition show significant undesirable side effects in humans. In retrospective studies anti-TNF biologics reduce the incidence and progression of CKD in humans. Whether TNF has a role in AKI-to-CKD transition and how TNF inhibition compares to EGFR inhibition is largely unknown. Methods Mice were subjected to bilateral renal ischemia-reperfusion injury or unilateral ureteral obstruction. Kidneys were analyzed by histology, immunohistochemistry, qPCR, western blot, mass cytometry, scRNA sequencing, and cytokine profiling. Results Here we show that TNF or EGFR inhibition reduce AKI-to-CKD transition and fibrosis equally by about 25%, while combination has no additional effect. EGFR inhibition reduced kidney TNF expression by about 50% largely by reducing accumulation of TNF expressing immune cells in the kidney early after AKI, while TNF inhibition did not affect EGFR activation or immune cell accumulation. Using scRNAseq data we show that TNF is predominantly expressed by immune cells in AKI but not in proximal tubule cells (PTC), and PTC-TNF knockout did not affect AKI-to-CKD transition in UUO. Thus, the anti-inflammatory and anti-fibrotic effects of the anti-TNF biologic etanercept in AKI-to-CKD transition rely on blocking TNF that is released from immune cells recruited or accumulating in response to PTC-EGFR signals. Conclusion Short-term anti-TNF biologics during or after AKI could be helpful in the prevention of AKI-to-CKD transition.

Global DNA hypermethylation and mitochondrial dysfunction are reported to be associated with the development of mild cognitive decline (MCI). The present study aims to generate preliminary data that connect the above association with post-surgical coronary artery bypass grafting (CABG) cognitive decline in patients. Data were collected from 70 CABG patients and 25 age-matched controls. Cognitive function was assessed using the Montreal Cognitive Assessment (MOCA) test on day 1 (before surgery) and on the day of discharge. Similarly, blood was collected before and one day after the CABG procedure for mitochondrial functional analysis and expression of DNA methylation genes. Test analysis score suggested 31 (44%) patients had MCI before discharge. These patients showed a significant decrease in complex I activity and an increase in malondialdehyde levels (p < 0.001) from the control blood samples. Post-surgical samples showed a significant reduction in blood MT-ND1 mRNA expression from control and from pre-surgical samples (p < 0.005), along with elevated DNMT1 gene expression (p < 0.047), with an insignificant increase in TET1 and TET3 gene expression. Correlation analysis showed a significant positive relation between cognitive decline and elevated blood DNMT1 and declined blood complex I activity, signifying that cognitive decline experienced by post-surgical CABG patients is associated with increased DNMT1 expression and declined complex I activity. Based on the data, we conclude that both DNA hypermethylation and mitochondrial dysfunction are associated with post-CABG MCI, where the former is negatively correlated, and the latter is positively correlated with post-surgical MCI in CABG cases. Additionally, a multimarker approach that comprises MOCA, DNA methylation, DNMT, and NQR activities can be utilized to stratify the population that is sensitive to developing post-CABG MCI.

TMEM106B, a lysosomal transmembrane protein, has been closely associated with brain health. Recently, an intriguing link between TMEM106B and brain inflammation has been discovered, but how TMEM106B regulates inflammation is unknown. Here, we report that TMEM106B deficiency in mice leads to reduced microglia proliferation and activation and increased microglial apoptosis in response to demyelination. We also found an increase in lysosomal pH and a decrease in lysosomal enzyme activities in TMEM106B-deficient microglia. Furthermore, TMEM106B loss results in a significant decrease in the protein levels of TREM2, an innate immune receptor essential for microglia survival and activation. Specific ablation of TMEM106B in microglia results in similar microglial phenotypes and myelination defects in mice, supporting the idea that microglial TMEM106B is critical for proper microglial activities and myelination. Moreover, the TMEM106B risk allele is associated with myelin loss and decreased microglial numbers in humans. Collectively, our study unveils a previously unknown role of TMEM106B in promoting microglial functionality during demyelination.

Tissue injury can drive secondary organ injury; however, mechanisms and mediators are not well understood. To identify interorgan cross-talk mediators, we used acute kidney injury (AKI)–induced acute lung injury (ALI) as a clinically important example. Using kidney and lung single-cell RNA sequencing after AKI in mice followed by ligand-receptor pairing analysis across organs, kidney ligands to lung receptors, we identify kidney-released circulating osteopontin (OPN) as a novel AKI-ALI mediator. OPN release from kidney tubule cells triggered lung endothelial leakage, inflammation, and respiratory failure. Pharmacological or genetic OPN inhibition prevented AKI-ALI. Transplantation of ischemic wt kidneys caused AKI-ALI, but not of ischemic OPN–global knockout kidneys, identifying kidney-released OPN as necessary interorgan signal to cause AKI-ALI. We show that OPN serum levels are elevated in patients with AKI and correlate with kidney injury. Our results demonstrate feasibility of using ligand-receptor analysis across organs to identify interorgan cross-talk mediators and may have important therapeutic implications in human AKI-ALI and multiorgan failure.

Multiorgan failure is devastating, and its mechanisms and mediators are not clear. Tissue injury in one organ appears to trigger disease in remote organs. Kidney and lung are frequently affected, such as when acute kidney injury (AKI) causes acute lung injury (ALI), a frequent clinical condition with high mortality. Here we identify factors secreted from the injured kidney that cause acute lung injury. We developed a murine model mimicking the generation of respiratory failure following acute kidney injury. To identify interorgan crosstalk mediators involved, we performed scRNAseq of mouse kidneys and lungs after AKI. We then applied ligand-receptor (L-R) pairing analysis across cells residing in kidney (ligands) or lung (receptors) to identify kidney-released circulating osteopontin (OPN) as a novel mediator of AKI-induced ALI (AKI-ALI). OPN release very early after AKI largely from tubule cells triggered neutrophil and macrophage infiltration into lungs associated with endothelial leakage, interstitial edema, and functional impairment. Pharmacological or genetic inhibition of OPN prevented AKI-ALI. Transplantation of ischemic wt kidneys into wt mice caused AKI-ALI, while transplantation of ischemic OPN-global-knockout kidneys failed to induce lung endothelial leakage and AKI-ALI, identifying circulating kidney-released OPN as sufficient to cause AKI-ALI in vivo. We show that AKI in humans results in elevations in OPN levels in the serum. Increased serum OPN levels in patients with multiorgan failure have been shown to positively correlate with reduced kidney function, respiratory failure, and mortality. Thus, our results identifying OPN as a mediator of AKI-ALI may have important therapeutic implications in human AKI-ALI and multiorgan failure.

Proximal-tubule-cell EGFR activation mediates tubule cell proliferation and repair early after kidney injury, while sustained EGFR activation causes kidney fibrosis. Inflammation is a key driver of AKI-to-CKD transition and fibrosis, but mechanisms of EGFR-driven profibrotic responses are not well understood. In a mouse model of AKI-to-CKD transition and CKD progression, we show that EGFR-inhibition significantly reduced kidney expression of many immunoregulatory molecules already by day two after injury, including the potent inflammatory cytokine tumor-necrosis-factor (TNF). Single nuclei RNA-sequencing analysis showed that macrophages were among the main early cellular sources of TNF in the injured kidney. In vitro, EGFR activation in macrophages increased macrophage TNF expression, while EGFR inhibition in vivo reduced kidney macrophage accumulation, as early as two days after injury. Thus, profibrotic EGFR signaling increases kidney TNF levels both directly and indirectly. TNF inhibition did not alter tubule EGFR activation and in contrast to EGFR inhibition did not reduce early macrophage accumulation in the kidney, suggesting that TNF does not promote early infiltration of immune cells in the kidney, but rather regulates profibrotic functions of kidney and/or immune cells. TNF inhibition with etanercept in vivo in AKI-injured mice downregulated a number of cytokines, including TNF itself. This cytokine downregulation overlapped with EGFR inhibition, and additional non-overlapping downregulated cytokines shared the same functions, predicting that TNF inhibition would prevent AKI-to-CKD transition like EGFR inhibition. Indeed, TNF-inhibition with etanercept reduced AKI-induced fibrosis to the same degree as the EGFR-inhibition, while the combination of both treatments showed no additive effect. In conclusion, our results identify TNF as a downstream effector of profibrotic EGFR activation and motivate the examination of TNF pathway inhibition in human AKI or CKD.Translational statementProximal tubule epidermal-growth-factor (EGFR) activation in mice and likely also in humans drives inflammation in the kidney after acute-kidney-injury (AKI) and causes chronic-kidney-disease (CKD) with fibrosis in a process termed AKI-to-CKD transition. Recent retrospective data shows that patients treated with TNF inhibitors show decreased incidence and progression of CKD. Our current work shows that TNF inhibition in mice is equally as effective as EGFR inhibition in preventing AKI-to-CKD transition and fibrosis. Thus, our results have translational potential and may stimulate examination of short-term TNF inhibition in AKI to prevent AKI-to-CKD transition or possibly of longer-term TNF inhibition in CKD to prevent CKD progression.