This study shows that the mTORC pathway is central to the antiphospholipid syndrome. Among patients with kidney transplants and antiphospholipid syndrome, 70% of those treated with sirolimus had ...long-term functioning allografts versus 12% of those not treated with sirolimus.
The antiphospholipid syndrome is an autoimmune disease characterized by the presence of circulating antiphospholipid antibodies that result in vascular thrombosis and obstetrical complications.
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The syndrome may be isolated or may occur in association with autoimmune disorders, such as systemic lupus erythematosus. Thrombotic events represent the major complication of the antiphospholipid syndrome,
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and to date, long-term anticoagulation has been the only treatment shown to reduce vascular complications. However, that regimen does not prevent organ deterioration and death in high-risk patients, particularly those in whom catastrophic antiphospholipid syndrome develops.
In addition to the thrombotic complications, vascular cellular infiltrates and fibrosis of the . . .
Organs and cells must adapt to shear stress induced by biological fluids, but how fluid flow contributes to the execution of specific cell programs is poorly understood. Here we show that shear ...stress favours mitochondrial biogenesis and metabolic reprogramming to ensure energy production and cellular adaptation in kidney epithelial cells. Shear stress stimulates lipophagy, contributing to the production of fatty acids that provide mitochondrial substrates to generate ATP through β-oxidation. This flow-induced process is dependent on the primary cilia located on the apical side of epithelial cells. The interplay between fluid flow and lipid metabolism was confirmed in vivo using a unilateral ureteral obstruction mouse model. Finally, primary cilium-dependent lipophagy and mitochondrial biogenesis are required to support energy-consuming cellular processes such as glucose reabsorption, gluconeogenesis and cytoskeletal remodelling. Our findings demonstrate how primary cilia and autophagy are involved in the translation of mechanical forces into metabolic adaptation.
mTOR activation is essential and sufficient to cause polycystic kidneys in Tuberous Sclerosis Complex (TSC) and other genetic disorders. In disease models, a sharp increase of proliferation and cyst ...formation correlates with a dramatic loss of oriented cell division (OCD). We find that OCD distortion is intrinsically due to S6 kinase 1 (S6K1) activation. The concomitant loss of S6K1 in Tsc1-mutant mice restores OCD but does not decrease hyperproliferation, leading to non-cystic harmonious hyper growth of kidneys. Mass spectrometry-based phosphoproteomics for S6K1 substrates revealed Afadin, a known component of cell-cell junctions required to couple intercellular adhesions and cortical cues to spindle orientation. Afadin is directly phosphorylated by S6K1 and abnormally decorates the apical surface of Tsc1-mutant cells with E-cadherin and α-catenin. Our data reveal that S6K1 hyperactivity alters centrosome positioning in mitotic cells, affecting oriented cell division and promoting kidney cysts in conditions of mTOR hyperactivity.
Mechanisms of progression of chronic kidney disease (CKD), a major health care burden, are poorly understood. EGFR stimulates CKD progression, but the molecular networks that mediate its biological ...effects remain unknown. We recently showed that the severity of renal lesions after nephron reduction varied substantially among mouse strains and required activation of EGFR. Here, we utilized two mouse strains that react differently to nephron reduction--FVB/N mice, which develop severe renal lesions, and B6D2F1 mice, which are resistant to early deterioration--coupled with genome-wide expression to elucidate the molecular nature of CKD progression. Our results showed that lipocalin 2 (Lcn2, also known as neutrophil gelatinase-associated lipocalin NGAL), the most highly upregulated gene in the FVB/N strain, was not simply a marker of renal lesions, but an active player in disease progression. In fact, the severity of renal lesions was dramatically reduced in Lcn2-/- mice. We discovered that Lcn2 expression increased upon EGFR activation and that Lcn2 mediated its mitogenic effect during renal deterioration. EGFR inhibition prevented Lcn2 upregulation and lesion development in mice expressing a dominant negative EGFR isoform, and hypoxia-inducible factor 1α (Hif-1α) was crucially required for EGFR-induced Lcn2 overexpression. Consistent with this, cell proliferation was dramatically reduced in Lcn2-/- mice. These data are relevant to human CKD, as we found that LCN2 was increased particularly in patients who rapidly progressed to end-stage renal failure. Together our results uncover what we believe to be a novel function for Lcn2 and a critical pathway leading to progressive renal failure and cystogenesis.
AKI leads to tubular injury and interstitial inflammation that must be controlled to avoid the development of fibrosis. We hypothesized that microRNAs are involved in the regulation of the balance ...between lesion formation and adaptive repair. We found that, under proinflammatory conditions, microRNA-146a (miR-146a) is transcriptionally upregulated by ligands of IL-1 receptor/Toll-like receptor family members via the activation of NF-κB in cultured renal proximal tubular cells. In vivo, more severe renal ischemia-reperfusion injury (IRI) associated with increased expression of miR-146a in both allografts and urine of human kidney transplant recipients, and unilateral IRI in mice induced miR-146a expression in injured kidneys. After unilateral IRI, miR-146a
mice exhibited more extensive tubular injury, inflammatory infiltrates, and fibrosis than wild-type mice. In vitro, overexpression or downregulation of miR-146a diminished or enhanced, respectively, IL-1 receptor-associated kinase 1 expression and induced similar effects on C-X-C motif ligand 8 (CXCL8)/CXCL1 expression by injured tubular cells. Moreover, inhibition of CXCL8/CXCL1 signaling prevented the development of inflammation and fibrosis after IRI in miR-146a
mice. In conclusion, these results indicate that miR-146a is a key mediator of the renal tubular response to IRI that limits the consequences of inflammation, a key process in the development of AKI and CKD.
In chronic kidney disease (CKD), loss of functional nephrons results in metabolic and mechanical stress in the remaining ones, resulting in further nephron loss. Here we show that Akt2 activation has ...an essential role in podocyte protection after nephron reduction. Glomerulosclerosis and albuminuria were substantially worsened in Akt2(-/-) but not in Akt1(-/-) mice as compared to wild-type mice. Specific deletion of Akt2 or its regulator Rictor in podocytes revealed that Akt2 has an intrinsic function in podocytes. Mechanistically, Akt2 triggers a compensatory program that involves mouse double minute 2 homolog (Mdm2), glycogen synthase kinase 3 (Gsk3) and Rac1. The defective activation of this pathway after nephron reduction leads to apoptosis and foot process effacement of the podocytes. We further show that AKT2 activation by mammalian target of rapamycin complex 2 (mTORC2) is also required for podocyte survival in human CKD. More notably, we elucidate the events underlying the adverse renal effect of sirolimus and provide a criterion for the rational use of this drug. Thus, our results disclose a new function of Akt2 and identify a potential therapeutic target for preserving glomerular function in CKD.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Epidermal growth factor receptor (EGFR) activation and lipocalin-2 (Lcn2) expression are frequently observed in the same pathological contexts, such as cancers or chronic kidney disease (CKD). ...However, the significance of this association is unknown. Here, we describe the role of Lcn2 in regulating EGFR trafficking. We show that Lcn2 increases EGFR cell surface abundance and is required for transforming growth factor α (TGF-α)-induced EGFR recycling to the plasma membrane and sustained activation. Lcn2 binds to the intracellular domain of EGFR in late endosomal compartments and inhibits its lysosomal degradation. Consistently, Lcn2 enhances EGFR-induced cell migration after TGF-α stimulation. In vivo, Lcn2 gene inactivation prevents EGFR recycling to the plasma membrane in an experimental model of CKD. Remarkably, this is associated with a dramatic decrease of renal lesions. Together, our data identify Lcn2 as a key mediator of EGFR trafficking processes. Hence, therapeutic inhibition of Lcn2 may counteract the deleterious effect of EGFR activation.
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•Lipocalin-2 (Lcn2) induces EGFR maintenance to the cell surface•Lcn2 facilitates EGFR recycling upon TGF-α stimulation•Cytosolic Lcn2 binds to EGFR in late endosomal compartments•Lcn2 allows sustained EGFR activation leading to chronic kidney disease onset
Yammine et al. propose lipocalin-2 (Lcn2) as a regulator of EGFR activity. By binding to TGF-α-activated EGFR intracellular domain, cytosolic Lcn2 enhances its recycling to the cell surface. This accounts for EGFR sustained activation leading to chronic kidney disease and makes Lcn2 a potential therapeutic target in this context.
Genetic studies have shown that the tuberous sclerosis complex (TSC) 1-TSC2-mammalian target of Rapamycin (mTOR) and the Hippo-Yes-associated protein 1 (YAP) pathways are master regulators of organ ...size, which are often involved in tumorigenesis. The crosstalk between these signal transduction pathways in coordinating environmental cues, such as nutritional status and mechanical constraints, is crucial for tissue growth. Whether and how mTOR regulates YAP remains elusive. Here we describe a novel mouse model of TSC which develops renal mesenchymal lesions recapitulating human perivascular epithelioid cell tumors (PEComas) from patients with TSC. We identify that YAP is up-regulated by mTOR in mouse and human PEComas. YAP inhibition blunts abnormal proliferation and induces apoptosis of TSC1-TSC2-deficient cells, both in culture and in mosaic Tsc1 mutant mice. We further delineate that YAP accumulation in TSC1/TSC2-deficient cells is due to impaired degradation of the protein by the autophagosome/lysosome system. Thus, the regulation of YAP by mTOR and autophagy is a novel mechanism of growth control, matching YAP activity with nutrient availability under growth-permissive conditions. YAP may serve as a potential therapeutic target for TSC and other diseases with dysregulated mTOR activity.
Kidney mass and function are sexually determined, but the cellular events and the molecular mechanisms involved in this dimorphism are poorly characterized. By combining female and male mice with ...castration/replacement experiments, we showed that male mice exhibited kidney overgrowth from five weeks of age. This effect was organ specific, since liver and heart weight were comparable between males and females, regardless of age. Consistently, the androgen receptor was found to be expressed in the kidneys of males, but not in the liver. In growing mice, androgens led to kidney overgrowth by first inducing a burst of cell proliferation and then an increase of cell size. Remarkably, androgens were also required to maintain cell size in adults. In fact, orchiectomy resulted in smaller kidneys in a matter of few weeks. These changes paralleled the changes of the expression of ornithine decarboxylase and cyclin D1, two known mediators of kidney growth, whereas, unexpectedly, mTORC1 and Hippo pathways did not seem to be involved. Androgens also enhanced kidney autophagy, very likely by increasing transcription factor EB nuclear translocation. Functionally, the increase of tubular mass resulted in increased sodium/phosphate transport. These findings were relevant to humans. Remarkably, by studying living gender-paired kidney donors-recipients, we showed that tubular cell size increased three months after transplantation in men as compared to women, regardless of the donor gender. Thus, our results identify novel signaling pathways that may be involved in androgen-induced kidney growth and homeostasis and suggest that androgens determine kidney size after transplantation.
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In chronic kidney disease (CKD), proteinuria results in severe tubulointerstitial lesions, which ultimately lead to end-stage renal disease. Here we identify 4-phenylbutyric acid (PBA), a chemical ...chaperone already used in humans, as a novel therapeutic strategy capable to counteract the toxic effect of proteinuria. Mechanistically, we show that albumin induces tubular unfolded protein response via cytosolic calcium rise, which leads to tubular apoptosis by Lipocalin 2 (LCN2) modulation through ATF4. Consistent with the key role of LCN2 in CKD progression, Lcn2 gene inactivation decreases ER stress-induced apoptosis, tubulointerstitial lesions and mortality in proteinuric mice. More importantly, the inhibition of this pathway by PBA protects kidneys from morphological and functional degradation in proteinuric mice. These results are relevant to human CKD, as LCN2 is increased in proteinuric patients. In conclusion, our study identifies a therapeutic strategy susceptible to improve the benefit of RAS inhibitors in proteinuria-induced CKD progression.
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