Peritoneal dialysis (PD) can result in chronic inflammation and progressive peritoneal membrane damage. Alanyl-Glutamine (Ala-Gln), a dipeptide with immunomodulatory effects, improved resistance of mesothelial cells to PD fluids. Recently, interleukin-17 (IL-17) was found to be associated with PD-induced peritoneal damage. Here we studied the capacity of intraperitoneal Ala-Gln administration to protect against peritoneal damage by modulating IL-17 expression in uremic rat and mouse PD exposure models. Supplementation of PD fluid with Ala-Gln resulted in reduced peritoneal thickness, αSMA expression and angiogenesis. Addition of Ala-Gln also attenuated the IL-17 pathway expression induced by PD, reflected by substantial reduction or normalization of peritoneal levels of IL-17, transforming growth factor β, IL-6, and the transcription factor retinoic acid receptor-related orphan receptor gamma T. Moreover, increased levels of IL-17 were associated with PD-induced peritoneal thickening. Conversely, Ala-Gln treatment prevented peritoneal extracellular matrix deposition, an effect seen with IL-17 blockade. Thus, intraperitoneal administration of Ala-Gln, a stable dipeptide commonly used in parenteral nutrition, ameliorates PD-induced peritoneal damage in animal models, in part by modulating IL-17 expression. Hence, Ala-Gln supplementation of dialysate may be a potential strategy to ameliorate peritoneal deterioration during PD.
Vitamin D deficiency is associated with a range of clinical disorders. To study the mechanisms involved and improve treatments, animal models are tremendously useful. Current vitamin D deficient rat models have important practical limitations, including time requirements when using, exclusively, a vitamin D deficient diet. More importantly, induction of hypovitaminosis D causes significant fluctuations in parathyroid hormone (PTH) and mineral levels, complicating the interpretation of study results. To overcome these shortcomings, we report the successful induction of vitamin D deficiency within three weeks, with stable serum PTH and minerals levels, in Wistar rats. We incorporated two additional manoeuvres compared to a conventional diet. Firstly, the vitamin D depleted diet is calcium (Ca) enriched, to attenuate the development of secondary hyperparathyroidism. Secondly, six intraperitoneal injections of paricalcitol during the first two weeks are given to induce the rapid degradation of circulating vitamin D metabolites. After three weeks, serum 25-hydroxyvitamin D3 (25D) and 1,25-dihydroxyvitamin D3 (1,25D) levels had dropped below detection limits, with unchanged serum PTH, Ca, and phosphate (P) levels. Therefore, this model provides a useful tool to examine the sole effect of hypovitaminosis D, in a wide range of research settings, without confounding changes in PTH, Ca, and P.
Patients with ESRD undergoing peritoneal dialysis develop progressive peritoneal fibrosis, which may lead to technique failure. Recent data point to Th17-mediated inflammation as a key contributor in peritoneal damage. The leukocyte antigen CD69 modulates the setting and progression of autoimmune and inflammatory diseases by controlling the balance between Th17 and regulatory T cells (Tregs). However, the relevance of CD69 in tissue fibrosis remains largely unknown. Thus, we explored the role of CD69 in fibroproliferative responses using a mouse model of peritoneal fibrosis induced by dialysis fluid exposure under either normal or uremic status. We found that cd69 mice compared with wild-type (WT) mice showed enhanced fibrosis, mesothelial to mesenchymal transition, IL-17 production, and Th17 cell infiltration in response to dialysis fluid treatment. Uremia contributed partially to peritoneal inflammatory and fibrotic responses. Additionally, antibody-mediated CD69 blockade in WT mice mimicked the fibrotic response of cd69 mice. Finally, IL-17 blockade in cd69 mice decreased peritoneal fibrosis to the WT levels, and mixed bone marrow from cd69 and Rag2c mice transplanted into WT mice reproduced the severity of the response to dialysis fluid observed in cd69 mice, showing that CD69 exerts its regulatory function within the lymphocyte compartment. Overall, our results indicate that CD69 controls tissue fibrosis by regulating Th17-mediated inflammation.
BackgroundDysfunctional endothelium may contribute to the development of cardiovascular complications in chronic kidney disease (CKD). Supplementation with active vitamin D has been proposed to have vasoprotective potential in CKD, not only by direct effects on the endothelium but also by an increment of α‐Klotho. Here, we explored the capacity of the active vitamin D analogue paricalcitol to protect against uremia‐induced endothelial damage and the extent to which this was dependent on increased α‐Klotho concentrations.Methods and ResultsIn a combined rat model of CKD with vitamin D deficiency, renal failure induced vascular permeability and endothelial‐gap formation in thoracic aorta irrespective of baseline vitamin D, and this was attenuated by paricalcitol. Downregulation of renal and serum α‐Klotho was found in the CKD model, which was not restored by paricalcitol. By measuring the real‐time changes of the human endothelial barrier function, we found that paricalcitol effectively improved the recovery of endothelial integrity following the addition of the pro‐permeability factor thrombin and the induction of a wound. Furthermore, immunofluorescence staining revealed that paricalcitol promoted vascular endothelial‐cadherin–based cell‐cell junctions and diminished F‐actin stress fiber organization, preventing the formation of endothelial intracellular gaps.ConclusionsOur results demonstrate that paricalcitol attenuates the CKD‐induced endothelial damage in the thoracic aorta and directly mediates endothelial stability in vitro by enforcing cell‐cell interactions.
Nuclear actin plays an important role in many processes that regulate gene expression. Cytoplasmic actin dynamics are tightly controlled by numerous actin-binding proteins, but regulation of nuclear actin has remained unclear. Here, we performed a genome-wide RNA interference (RNAi) screen in Drosophila cells to identify proteins that influence either nuclear polymerization or import of actin. We validate 19 factors as specific hits, and show that Chinmo (known as Bach2 in mammals), SNF4Aγ (Prkag1 in mammals) and Rab18 play a role in nuclear localization of actin in both fly and mammalian cells. We identify several new regulators of cofilin activity, and characterize modulators of both cofilin kinases and phosphatase. For example, Chinmo/Bach2, which regulates nuclear actin levels also in vivo, maintains active cofilin by repressing the expression of the kinase Cdi (Tesk in mammals). Finally, we show that Nup98 and lamin are candidates for regulating nuclear actin polymerization. Our screen therefore reveals new aspects of actin regulation and links nuclear actin to many cellular processes.
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