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Myeloid-specific ferritin light chain deletion does not confer renal protection in sepsis-associated acute kidney injury

ABSTRACT: Sepsis-associated acute kidney injury (SA-AKI) is a key contributor to the life threatening sequalae attributed to sepsis. Mechanistically, SA-AKI is a consequence of unabated myeloid cell activation and oxidative stress that induces tubular injury. Iron mediates inflammatory pathways directly and through regulating the expression of myeloid-derived ferritin, an iron storage protein comprised of ferritin light (FtL) and ferritin heavy chain (FtH) subunits. Previous work revealed myeloid FtH deletion leads to a compensatory increase in intracellular and circulating FtL and is associated with amelioration of SA-AKI. We designed this study to test the hypothesis that loss of myeloid FtL and subsequently, circulating FtL will exacerbate the sepsis-induced inflammatory response and worsen SA-AKI. We generated a novel myeloid-specific FtL knockout mouse (FtLLysM-/-) and induced sepsis via cecal ligation and puncture or lipopolysaccharide endotoxemia. As expected, serum ferritin levels were significantly lower in the knockout mice, suggesting that myeloid cells dominantly contribute to circulating ferritin. Interestingly, while sepsis induction led to a marked production of pro- and anti-inflammatory cytokines, there was no statistical difference between the genotypes. There was a similar loss of kidney function, as evident by a rise in serum creatinine and cystatin C, and renal injury identified by expression of kidney injury molecule-1 and neutrophil gelatinase associated lipocalin. Finally, RNA sequencing revealed upregulation of pathways for cell cycle arrest and autophagy post-sepsis, but no significant differences were observed between genotypes, including in key genes associated with ferroptosis, an iron-mediated form of cell death. The loss of FtL did not impact sepsis-mediated activation of NFkB or HIF-1a signaling, key inflammatory pathways associated with dysregulated host response. Taken together, while FtL overexpression was shown to be protective against sepsis, loss of FtL did not influence sepsis pathogenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE255281 | GEO | 2024/05/13

REPOSITORIES: GEO

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Project description:# Background Acute kidney injury (AKI) in sepsis patients increases patient mortality. Endothelial cells are important players in the pathophysiology of sepsis-associated AKI (SA-AKI), yet knowledge regarding their spatiotemporal involvement in coagulation disbalance and leukocyte recruitment is lacking. This study investigated the identity and kinetics of responses of different microvascular compartments in kidney cortex in response to SA-AKI. # Methods Laser microdissected arterioles, glomeruli, peritubular capillaries, and postcapillary venules from kidneys of mice subjected to cecal ligation and puncture (CLP) were analyzed using RNA sequencing. Differential expression and pathway enrichment analyses identified genes involved in coagulation and inflammation. A selection of these genes was evaluated by RT-qPCR in microvascular compartments of renal biopsies from patients with SA-AKI. The role of two identified genes in lipopolysaccharide-induced endothelial coagulation and inflammatory activation were determined in vitro in HUVEC using siRNA-based gene silencing. # Results CLP-sepsis in mice induced altered expression of approximately 400 genes in the renal microvasculature, with microvascular compartments exhibiting unique spatiotemporal responses. In mice, changes in gene expression related to coagulation and inflammation were most extensive in glomeruli at early and intermediate time points, with high induction of Plat, Serpine1, Thbd, Icam1, Stat3, and Ifitm3. In human SA-AKI, PROCR and STAT3 were induced in postcapillary venules, while SERPINE1 expression was diminished. IFITM3 was increased in arterioles and glomeruli. In vitro studies revealed that STAT3 and IFITM3 partly control endothelial coagulation and inflammatory activation. # Conclusion Renal microvascular compartments in mice and humans exhibited heterogeneous changes in coagulation- and inflammation-related gene expression in response to SA-AKI. Additional research should aim at understanding the functional consequences of the here described heterogeneous microvascular responses to establish the usefulness of identified genes as therapeutic targets in SA-AKI.

Project description:Sepsis is a severe and dysregulated inflammatory disease that often precedes the development of acute kidney injury (AKI) with consequent worsening outcome. The main characteristics of sepsis-induced AKI include endothelial cell (EC) dysfunction, infiltration of inflammatory cells, glomerular thrombosis, and renal tubular epithelial cells (RTEC) injury. Numerous studies have demonstrated that mammalian target of rapamycin (mTOR) activation has been implicated in the initiation and progression of renal injury in course of sepsis. However, little is known, about the molecular basis of mTOR role in EC and RTEC dysfunction. Here, we evaluate whether mTOR inhibition by Rapamycin (Rp) as potential strategy to ameliorate renal function and dissected the molecular mechanisms involved. In a mouse model of lipopolysaccharide (LPS)-induced AKI , LPS injection led to a time-dependent increase of serum creatinine and significant morphological changes in renal parenchyma associated with increased collagen deposits and endothelial dysfunction. Interestingly, Rp treatment significantly decreased creatine levels and preserved renal parenchyma, counteracting Endothelial-to mesenchymal transition (EndMT) process and early fibrosis through the inhibition of ERK pathway. Next, we examined the effects of LPS-TLR4 interaction in RTECs. Through a whole-genome DNA methylation analysis in cultured RTEC, we found that LPS induced aberrant methylation, particularly in regions involved in premature aging. The most represented genes were CD39 and WFS1. LPS stimulation of RTEC led to up-regulation of SA-β Gal and cell cycle arrest markers such as p21. In accordance, in endotoxemic mice, we found a decreased expression of CD39 concurrent with Klotho down-regulation. Administration of Rp exerted anti-aging effects in endotoxemic mice, preserving CD39 and Klotho expression. In conclusion, we demonstrated that mTOR inhibition could offer novel strategies to protect endothelial and tubular compartment from accelerated aging and fibrosis thus counteracting the progression to chronic kidney disease.

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Myeloid-specific ferritin light chain deletion does not confer renal protection in sepsis-associated acute kidney injury

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