TREM1/3 deficiency impairs tissue repair after acute kidney injury and mitochondrial metabolic flexibility in tubular epithelial cells

Long-term sequelae of acute kidney injury (AKI) are associated with incomplete recovery of renal function and the development of chronic kidney disease (CKD), which can be mediated by aberrant innate immune activation, mitochondrial pathology, and accumulation of senescent tubular epithelial cells (TECs). Herein, we show that the innate immune receptor Triggering receptor expressed on myeloid cells-1 (TREM-1) links mitochondrial metabolism to tubular epithelial senescence. TREM-1 is expressed by inflammatory and epithelial cells, both players in renal repair after ischemia/reperfusion (IR)-induced AKI. Hence, we subjected WT and TREM1/3 KO mice to different models of renal IR. TREM1/3 KO mice displayed no major differences during the acute phase of injury, but increased mortality was observed in the recovery phase. This detrimental effect was associated with maladaptive repair, characterized by persistent tubular damage, inflammation, fibrosis, and TEC senescence. In vitro, we observed an altered mitochondrial homeostasis and cellular metabolism in TREM1/3 KO primary TECs. This was associated with G2/M arrest and increased ROS accumulation. Further exposure of cells to ROS-generating triggers drove the cells into a stress-induced senescent state, resulting in decreased wound healing capacity. Treatment with a mitochondria anti-oxidant partly prevented the senescent phenotype, suggesting a role for mitochondria herein. In summary, we have unraveled a novel (metabolic) mechanism by which TREM1/3 deficiency drives senescence in TECs. This involves redox imbalance, mitochondrial dysfunction and a decline in cellular metabolic activities. These finding suggest a novel role for TREM-1 in maintaining tubular homeostasis through regulation of mitochondrial metabolic flexibility

Gcase and limp2 abnormalities in the liver of niemann pick type c mice

Funding Information: This work was supported by the NWO-Building Blocks of Life: GlcCer grant to J.M.F.G.A: BBOL-2007247202. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.The lysosomal storage disease Niemann–Pick type C (NPC) is caused by impaired cholesterol efflux from lysosomes, which is accompanied by secondary lysosomal accumulation of sph-ingomyelin and glucosylceramide (GlcCer). Similar to Gaucher disease (GD), patients deficient in glucocerebrosidase (GCase) degrading GlcCer, NPC patients show an elevated glucosylsphingosine and glucosylated cholesterol. In livers of mice lacking the lysosomal cholesterol efflux transporter NPC1, we investigated the expression of established biomarkers of lipid-laden macrophages of GD patients, their GCase status, and content on the cytosol facing glucosylceramidase GBA2 and lysoso-mal integral membrane protein type B (LIMP2), a transporter of newly formed GCase to lysosomes. Livers of 80-week-old Npc1−/− mice showed a partially reduced GCase protein and enzymatic activity. In contrast, GBA2 levels tended to be reciprocally increased with the GCase deficiency. In Npc1−/− liver, increased expression of lysosomal enzymes (cathepsin D, acid ceramidase) was observed as well as increased markers of lipid-stressed macrophages (GPNMB and galectin-3). Im-munohistochemistry showed that the latter markers are expressed by lipid laden Kupffer cells. Earlier reported increase of LIMP2 in Npc1−/− liver was confirmed. Unexpectedly, immunohistochemistry showed that LIMP2 is particularly overexpressed in the hepatocytes of the Npc1−/− liver. LIMP2 in these hepatocytes seems not to only localize to (endo)lysosomes. The recent recognition that LIMP2 harbors a cholesterol channel prompts the speculation that LIMP2 in Npc1−/− hepatocytes might mediate export of cholesterol into the bile and thus protects the hepatocytes.publishersversionpublishe

Reducing GBA2 activity ameliorates neuropathology in niemann-pick type C mice

The enzyme glucocerebrosidase (GBA) hydrolyses glucosylceramide (GlcCer) in lysosomes. Markedly reduced GBA activity is associated with severe manifestations of Gaucher disease including neurological involvement. Mutations in the GBA gene have recently also been identified as major genetic risk factor for Parkinsonism. Disturbed metabolism of GlcCer may therefore play a role in neuropathology. Besides lysosomal GBA, cells also contain a non-lysosomal glucosylceramidase (GBA2). Given that the two β-glucosidases share substrates, we speculated that over-activity of GBA2 during severe GBA impairment might influence neuropathology. This hypothesis was studied in Niemann-Pick type C (Npc1-/-) mice showing secondary deficiency in GBA in various tissues. Here we report that GBA2 activity is indeed increased in the brain of Npc1-/- mice. We found that GBA2 is particularly abundant in Purkinje cells (PCs), one of the most affected neuronal populations in NPC disease. Inhibiting GBA2 in Npc1-/- mice with a brain-permeable low nanomolar inhibitor significantly improved motor coordination and extended lifespan in the absence of correction in cholesterol and ganglioside abnormalities. This trend was recapitulated, although not to full extent, by introducing a genetic loss of GBA2 in Npc1-/- mice. Our findings point to GBA2 activity as therapeutic target in NPC

Nicotine Protects Kidney from Renal Ischemia/Reperfusion Injury through the Cholinergic Anti-Inflammatory Pathway

Kidney ischemia/reperfusion injury (I/R) is characterized by renal dysfunction and tubular damages resulting from an early activation of innate immunity. Recently, nicotine administration has been shown to be a powerful inhibitor of a variety of innate immune responses, including LPS-induced toxaemia. This cholinergic anti-inflammatory pathway acts via the α7 nicotinic acetylcholine receptor (α7nAChR). Herein, we tested the potential protective effect of nicotine administration in a mouse model of renal I/R injury induced by bilateral clamping of kidney arteries. Renal function, tubular damages and inflammatory response were compared between control animals and mice receiving nicotine at the time of ischemia. Nicotine pretreatment protected mice from renal dysfunction in a dose-dependent manner and through the α7nAChR, as attested by the absence of protection in α7nAChR-deficient mice. Additionally, nicotine significantly reduced tubular damages, prevented neutrophil infiltration and decreased productions of the CXC-chemokine KC, TNF-α and the proinflammatory high-mobility group box 1 protein. Reduced tubular damage in nicotine pre-treated mice was associated with a decrease in tubular cell apoptosis and proliferative response as attested by the reduction of caspase-3 and Ki67 positive cells, respectively. All together, these data highlight that nicotine exerts a protective anti-inflammatory effect during kidney I/R through the cholinergic α7nAChR pathway. In addition, this could provide an opportunity to overcome the effect of surgical cholinergic denervation during kidney transplantation

S100A8/A9 Is Not Involved in Host Defense against Murine Urinary Tract Infection

Background: Inflammation is commonly followed by the release of endogenous proteins called danger associated molecular patterns (DAMPs) that are able to warn the host for eminent danger. S100A8/A9 subunits are DAMPs that belong to the S100 family of calcium binding proteins. S100A8/A9 complexes induce an inflammatory response and their expression correlates with disease severity in several inflammatory disorders. S100A8/A9 promote endotoxin-and Escherichia (E.) coli-induced sepsis showing its contribution in systemic infection. The role of S100A8/A9 during a local infection of the urinary tract system caused by E. coli remains unknown. Methodology/Principal Findings: We investigated the contribution of S100A8/A9 in acute urinary tract infection (UTI) by instilling 2 different doses of uropathogenic E. coli transurethrally in wild type (WT) and S100A9 knockout (KO) mice. Subsequently, we determined bacterial outgrowth, neutrophilic infiltrate and inflammatory mediators in bladder and kidney 24 and 48 hours later. UTI resulted in a substantial increase of S100A8/A9 protein in bladder and kidney tissue of WT mice. S100A9 KO mice displayed similar bacterial load in bladder or kidney homogenate compared to WT mice using 2 different doses at 2 different time points. S100A9 deficiency had little effect on the inflammatory responses to E. Coli-induced UTI infection, as assessed by myeloperoxidase activity in bladder and kidneys, histopathologic analysis, and renal and bladder cytokine concentrations. Conclusions: We show that despite high S100A8/A9 expression in bladder and kidney tissue upon UTI, S100A8/A9 does not contribute to an effective host response against E. Coli in the urinary tract syste

The Role of Toll-Like Receptor 2 in Inflammation and Fibrosis during Progressive Renal Injury

Tissue fibrosis and chronic inflammation are common causes of progressive organ damage, including progressive renal disease, leading to loss of physiological functions. Recently, it was shown that Toll-like receptor 2 (TLR2) is expressed in the kidney and activated by endogenous danger signals. The expression and function of TLR2 during renal fibrosis and chronic inflammation has however not yet been elucidated. Therefore, we studied TLR2 expression in human and murine progressive renal diseases and explored its role by inducing obstructive nephropathy in TLR2−/− or TLR2+/+ mice. We found that TLR2 is markedly upregulated on tubular and tubulointerstitial cells in patients with chronic renal injury. In mice with obstructive nephropathy, renal injury was associated with a marked upregulation and change in distribution of TLR2 and upregulation of murine TLR2 danger ligands Gp96, biglycan, and HMGB1. Notably, TLR2 enhanced inflammation as reflected by a significantly reduced influx of neutrophils and production of chemokines and TGF-β in kidneys of TLR2−/− mice compared with TLR2+/+ animals. Although, the obstructed kidneys of TLR2−/− mice had less interstitial myofibroblasts in the later phase of obstructive nephropathy, tubular injury and renal matrix accumulation was similar in both mouse strains. Together, these data demonstrate that TLR2 can initiate renal inflammation during progressive renal injury and that the absence of TLR2 does not affect the development of chronic renal injury and fibrosis

Experimental thrombocytopenia does not affect acute kidney injury 24 hours after renal ischemia reperfusion in mice

The pathophysiology of renal ischemia/reperfusion (I/R) injury is characterized by excessive activation of inflammation and coagulation processes followed by abnormal renal tissue repair, resulting in renal injury and function loss. Platelets are important actors in these processes, however to what extent platelets contribute to the pathophysiology of renal I/R injury still needs to be elucidated. In the current study, we treated wild-type mice with a platelet depleting antibody, which caused thrombocytopenia. We then investigated the role of platelets during the pathophysiology of renal I/R by subjecting control wild-type mice with normal platelet counts and thrombocytopenic wild-type mice to renal I/R injury. Our results showed that in the early phase of renal I/R injury, thrombocytopenia 24 hours after ischemia reperfusion does not influence renal injury, neutrophil infiltration and accumulation of inflammatory chemokines (e.g. keratinocyte chemoattractant, monocyte chemoattractant protein 1, tumor necrosis factor alpha). In the recovery and regeneration phase of I/R injury, respectively 5 and 10 days post-ischemia, thrombocytopenia did also not affect the accumulation of intra-renal neutrophils and macrophages, renal injury, and renal fibrosis. Together, these results imply that lowering platelet counts do not impact the pathogenesis of I/R injury in mice

Hematopoietic stem cell mobilization therapy accelerates recovery of renal function independent of stem cell contribution

Acute renal failure and tubular cell loss as a result of ischemia constitute major challenges in renal pathophysiology. Increasing evidence suggests important roles for bone marrow stem cells in the regeneration of renal tissue after injury. This study investigated whether the enhanced availability of hematopoietic stem cells, induced by stem cell factor and granulocyte colony-stimulating factor, to the injured kidney provides an adequate strategy for stem cell-based therapy to counteract renal ischemia/reperfusion injury. It is interesting that cytokine treatment before injury resulted in significant enhancement of function recovery of the kidney. This, however, was not due to increased incorporation of tubular epithelial cells from bone marrow origin. Importantly, cytokine treatment resulted in impaired influx of granulocytes into the injured kidney. Although cytokine treatment improved renal function rapidly after ischemic injury, the results show that the underlying mechanism likely is not based on stem cell transdifferentiation but rather on altered inflammatory kinetic

CD44v3-v10 reduces the profibrotic effects of TGF-β1 and attenuates tubular injury in the early stage of chronic obstructive nephropathy

CD44 family members are cell surface glycoproteins, which are expressed on tubular epithelial cells (TEC) solely upon kidney injury and are involved in renal fibrosis development. Renal interstitial fibrosis is the final manifestation of chronic kidney diseases and is regulated by a complex network of cytokines, including the profibrotic factor transforming growth factor-β1 (TGF-β1) and the two antifibrotic cytokines bone morphogenic protein-7 (BMP-7) and hepatocyte growth factor (HGF). The present study investigates the potential role of CD44 standard (CD44s) and CD44v3-v10 (CD44v3) isoforms as modulators of the balance between TGF-β1 and HGF/BMP-7. CD44s is the shortest and most common isoform. CD44v3-v10 (CD44v3) has heparan sulfate moieties, which enable the binding to HGF/BMP-7, and hence, might exert renoprotective effects. Using transgenic mice overexpressing either CD44s or CD44v3 specifically on proximal TEC, we found that in vitro the overexpression of CD44v3 on primary TEC renders cells less susceptible to TGF-β1 profibrotic actions and more sensitive to BMP-7 and HGF compared with TEC overexpressing CD44s. One day after unilateral ureteric obstruction, obstructed kidneys from CD44v3 transgenic mice showed less tubular damage and myofibroblasts accumulation, which was associated with decreased TGF-β1 signaling and increased BMP-7 synthesis and signaling compared with kidneys from wild-type and CD44s transgenic mice. These data suggest that CD44v3 plays a renoprotective role in early stage of chronic obstructive nephropath