Interleukin-13 promotes expression of Alix to compromise renal tubular epithelial barrier function

Sodium butyrate ameliorated diabetic nephropathy-associated tubulointerstitial inflammation by modulating the tight junctions of renal tubular epithelial cells

As one of the most significant pathological changes of diabetic nephropathy (DN), tubulointerstitial fibrosis (TIF) had a close relationship with tubulointerstitial inflammation (TI), and the occurrence of TI could have resulted from the disrupted tight junctions (TJs) of renal tubular epithelial cells (RTECs). Studies have demonstrated that sodium butyrate (NaB), a typical short chain fatty acid (SCFA), played an important regulatory role in intestinal TJs and inflammation. In this study, our in vivo and in vitro results showed that accompanied by TI, renal tubular TJs were gradually disrupted in the process of DN-related TIF. In HG and LPS co-cultured HK-2 cells and db/db mice, NaB treatment regained the TJs of RTECs via the sphingosine 1-phosphate receptor-1 (S1PR1)/AMPK signaling pathway, relieving inflammation. Small interfering RNA of S1PR1, S1PR1 antagonist W146 and agonist SEW2871, and AMPK agonist AICAR were all used to further confirm the essential role of the S1PR1/AMPK signaling pathway in NaB's TJ protection in RTECs in vitro. Finally, NaB administration not only improved the renal function and TIF, but also relieved the TI of db/db mice. These findings suggested that the use of NaB might be a potential adjuvant treatment strategy for DN-associated TIF, and this protective effect was linked to the TJ modulation of RTECs via the S1PR1/AMPK signaling pathway, leading to the improvement of TI.

LncRNA446 Regulates Tight Junctions by Inhibiting the Ubiquitinated Degradation of Alix after Porcine Epidemic Diarrhea Virus Infection

Porcine epidemic diarrhea (PED) is a highly contagious disease, caused by porcine epidemic diarrhea virus (PEDV), which causes huge economic losses. Tight junction-associated proteins play an important role during virus infection; therefore, maintaining their integrity may be a new strategy for the prevention and treatment of PEDV. Long noncoding RNAs (lncRNAs) participate in numerous cellular functional activities, yet whether and how they regulate the intestinal barrier against viral infection remains to be elucidated. Here, we established a standard system for evaluating intestinal barrier integrity and then determined the differentially expressed lncRNAs between PEDV-infected and healthy piglets by lncRNA-seq. A total of 111 differentially expressed lncRNAs were screened, and lncRNA446 was identified due to significantly higher expression after PEDV infection. Using IPEC-J2 cells and intestinal organoids as in vitro models, we demonstrated that knockdown of lncRNA446 resulted in increased replication of PEDV, with further damage to intestinal permeability and tight junctions. Mechanistically, RNA pulldown and an RNA immunoprecipitation (RIP) assay showed that lncRNA446 directly binds to ALG-2-interacting protein X (Alix), and lncRNA446 inhibits ubiquitinated degradation of Alix mediated by TRIM25. Furthermore, Alix could bind to ZO1 and occludin and restore the expression level of the PEDV M gene and TJ proteins after lncRNA446 knockdown. Additionally, Alix knockdown and overexpression affects PEDV infection in IPEC-J2 cells. Collectively, our findings indicate that lncRNA446, by inhibiting the ubiquitinated degradation of Alix after PEDV infection, is involved in tight junction regulation. This study provides new insights into the mechanisms of intestinal barrier resistance and damage repair triggered by coronavirus. IMPORTANCE Porcine epidemic diarrhea is an acute, highly contagious enteric viral disease severely affecting the pig industry, for which current vaccines are inefficient due to the high variability of PEDV. Because PEDV infection can lead to severe injury of the intestinal epithelial barrier, which is the first line of defense, a better understanding of the related mechanisms may facilitate the development of new strategies for the prevention and treatment of PED. Here, we demonstrate that the lncRNA446 directly binds one core component of the actomyosin-tight junction complex named Alix and inhibits its ubiquitinated degradation. Functionally, the lncRNA446/Alix axis can regulate the integrity of tight junctions and potentially repair intestinal barrier injury after PEDV infection.

The role of CDX2 in renal tubular lesions during diabetic kidney disease

Renal tubules are vulnerable targets of various factors causing kidney injury in diabetic kidney disease (DKD), and the degree of tubular lesions is closely related to renal function. Abnormal renal tubular epithelial cells (RTECs) differentiation and depletion of cell junction proteins are important in DKD pathogenesis. Caudal-type homeobox transcription factor 2 (CDX2), represents a key nuclear transcription factor that maintains normal proliferation and differentiation of the intestinal epithelium. The present study aimed to evaluate the effects of CDX2 on RTECs differentiation and cell junction proteins in DKD. The results demonstrated that CDX2 was mainly localized in renal tubules, and downregulated in various DKD models. CDX2 upregulated E-cadherin and suppressed partial epithelial-mesenchymal transition (EMT), which can alleviate hyperglycemia-associated RTECs injury. Cystic fibrosis transmembrane conductance regulator (CFTR) was regulated by CDX2 in NRK-52E cells, and CFTR interfered with β-catenin activation by binding to Dvl2, which is an essential component of Wnt/β-catenin signaling. CFTR knockdown abolished the suppressive effects of CDX2 on Wnt/β-catenin signaling, thereby upregulating cell junction proteins and inhibiting partial EMT in RTECs. In summary, CDX2 can improve renal tubular lesions during DKD by increasing CFTR amounts to suppress the Wnt/β-catenin signaling pathway.

The role of Alix in the proliferation of human glioma cells

Apoptosis-linked-gene-2-interacting protein 1 (Alix) is involved in the endosome-lysosome system in the cytoplasm. The normal function of Alix may be altered by ALG-2 toward a destructive role during active cell death. Alix also may play a role in regulation of cell proliferation. However, the role of Alix in human glioma has not been elucidated yet. This study intended to clarify the relationship between Alix and glioma pathologic grades and its role in the proliferation of glioma cells. Our findings showed that Alix protein concentrations were significantly elevated in high-grade glioma tissue compared with low-grade glioma (P < .0001). Immunohistochemical study revealed that Alix was overexpressed in 75 resected glioma tissues and may forecast poor survival. Alix expression was increased in resting serum-stimulated glioma cells. Additionally, we reduced Alix expression in U251MG cells and then found that cell viability was decreased significantly when p21 expression increased. Colony formation assay and flow cytometry analysis demonstrated that reduced Alix expression may lead to growth inhibition and cell cycle arrest. In summary, our findings suggest that Alix plays an important role in the proliferation of glioma cells and may be a novel therapeutic target.