Reevaluation of Lung Injury in TNF-Induced Shock: The Role of the Acid Sphingomyelinase.

Tumor necrosis factor (TNF) is a well-known mediator of sepsis. In many cases, sepsis results in multiple organ injury including the lung with acute respiratory distress syndrome (ARDS). More than 20-year-old studies have suggested that TNF may be directly responsible for organ injury during sepsis. However, these old studies are inconclusive, because they relied on human rather than conspecific TNF, which was contaminated with endotoxin in most studies. In this study, we characterized the direct effects of intravenous murine endotoxin-free TNF on cardiovascular functions and organ injury in mice with a particular focus on the lungs. Because of the relevance of the acid sphingomyelinase in sepsis, ARDS, and caspase-independent cell death, we also included acid sphingomyelinase-deficient (ASM-/-) mice. ASM-/- and wild-type (WT) mice received 50 µg endotoxin-free murine TNF intravenously alone or in combination with the pan-caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (zVAD) and were ventilated at low tidal volume while lung mechanics were followed. Blood pressure was stabilized by intra-arterial fluid support, and body temperature was kept at 37°C to delay lethal shock and to allow investigation of blood gases, lung histopathology, proinflammatory mediators, and microvascular permeability 6 hours after TNF application. Besides the lungs, also the kidneys and liver were examined. TNF elicited the release of inflammatory mediators and a high mortality rate, but failed to injure the lungs, kidneys, or liver of healthy mice significantly within 6 hours. Mortality in WT mice was most likely due to sepsis-like shock, as indicated by metabolic acidosis, high procalcitonin levels, and cardiovascular failure. ASM-/- mice were protected from TNF-induced hypotension and reflex tachycardia and also from mortality. In WT mice, intravenous exogenous TNF does not cause organ injury but induces a systemic inflammatory response with cardiovascular failure, in which the ASM plays a role.

YB-1 increases glomerular, but decreases interstitial fibrosis in CNI-induced nephropathy.

Calcineurin inhibitors (CNIs) are a cornerstone of the current treatment in solid organ transplantation and autoimmune disease. However, CNIs also bear deleterious effects as they cause glomerular and tubulointerstitial fibrosis in the kidney. We recently identified Y-box protein-1 (YB-1) as a novel downstream effector of CNI-signaling in the cytoplasm of glomerular cells. In the present study, we corroborate the pro-fibrotic role of YB-1 in glomeruli of patients under CNI-treatment. Such effects in glomeruli are significantly mitigated in CNI-treated mice with half-normal YB-1 expression (Yb1+/-). Surprisingly, in the tubulointerstitium we observe an opposite role of the CNI-YB-1 axis. Here, YB-1 is predominantly located to the nuclei and represses transcription of several extracellular matrix genes. Consistently, CNI-treatment in Yb1+/- mice markedly increases pro-fibrotic changes in the tubulointerstitium. In summary, our data provide evidence that fibrotic CNI-induced YB-1 effects in glomerular cells need to be contrasted with beneficial anti-fibrotic effects in the tubulointerstitium.

YB-1 orchestrates onset and resolution of renal inflammation via IL10 gene regulation.

The Y-box-binding protein (YB)-1 plays a non-redundant role in both systemic and local inflammatory response. We analysed YB-1-mediated expression of the immune regulatory cytokine IL-10 in both LPS and sterile inflammation induced by unilateral renal ischaemia-reperfusion (I/R) and found an important role of YB-1 not only in the onset but also in the resolution of inflammation in kidneys. Within a decisive cis-regulatory region of the IL10 gene locus, the fourth intron, we identified and characterized an operative YB-1 binding site via gel shift experiments and reporter assays in immune and different renal cells. In vivo, YB-1 phosphorylated at serine 102 localized to the fourth intron, which was paralleled by enhanced IL-10 mRNA expression in mice following LPS challenge and in I/R. Mice with half-maximal expression of YB-1 (Yb1+/- ) had diminished IL-10 expression upon LPS challenge. In I/R, Yb1+/- mice exhibited ameliorated kidney injury/inflammation in the early-phase (days 1 and 5), however showed aggravated long-term damage (day 21) with increased expression of IL-10 and other known mediators of renal injury and inflammation. In conclusion, these data support the notion that there are context-specific decisions concerning YB-1 function and that a fine-tuning of YB-1, for example, via a post-translational modification regulates its activity and/or localization that is crucial for systemic processes such as inflammation.

Therapeutic nuclear shuttling of YB-1 reduces renal damage and fibrosis.

Virtually all chronic kidney diseases progress towards tubulointerstitial fibrosis. In vitro, Y-box protein-1 (YB-1) acts as a central regulator of gene transcription and translation of several fibrosis-related genes. However, it remains to be determined whether its pro- or antifibrotic propensities prevail in disease. Therefore, we investigated the outcome of mice with half-maximal YB-1 expression in a model of renal fibrosis induced by unilateral ureteral obstruction. Yb1+/- animals displayed markedly reduced tubular injury, immune cell infiltration and renal fibrosis following ureteral obstruction. The increase in renal YB-1 was limited to a YB-1 variant nonphosphorylated at serine 102 but phosphorylated at tyrosine 99. During ureteral obstruction, YB-1 localized to the cytoplasm, directly stabilizing Col1a1 mRNA, thus promoting fibrosis. Conversely, the therapeutic forced nuclear compartmentalization of phosphorylated YB-1 by the small molecule HSc025 mediated repression of the Col1a1 promoter and attenuated fibrosis following ureteral obstruction. Blunting of these effects in Yb1+/- mice confirmed involvement of YB-1. HSc025 even reduced tubulointerstitial damage when applied at later time points during maximum renal damage. Thus, phosphorylation and subcellular localization of YB-1 determines its effect on renal fibrosis in vivo. Hence, induced nuclear YB-1 shuttling may be a novel antifibrotic treatment strategy in renal diseases with the potential of damage reversal.