Renal tubular epithelial cells (RTECs) apoptosis is the key factor in the development of diabetic kidney disease (DKD). Endoplasmic reticulum stress (ERS) leading to mitochondrial Ca2+ overload is one of the causes of apoptosis in RTECs. Corni Fructus (CF) is an herbal medicine, developed and applied as a functional food, and it is commonly used to treat DKD. Cornuside (Cor) is one of the main chemical components in CF. This research seeks to investigate the function of Cor in DKD and delve into its possible mechanisms. Cor significantly improved renal function and ameliorated renal pathological changes of db/db mice. Bioinformatics analyses suggested that the modulation of endoplasmic reticulum-induced intrinsic apoptosis pathway was a primary mechanism by which Cor ameliorated DKD. TUNEL assays and flow cytometry assays indicated that Cor effectively inhibited RTECs apoptosis in db/db mice and AGE-induced HK-2 cells. Further experimental studies showed that Cor mitigated ERS by inhibiting the activation of PERK/ATF4/CHOP signal pathway and down-regulation of VDAC1 protein expression, thus alleviating mitochondrial Ca2+ overload. More importantly, Cor directly targeted NEDD4 to facilitate VDAC1 degradation. Notably, the silencing of NEDD4 nearly abolished Cor's inhibitory effects on mitochondrial Ca2+ overload and apoptosis. In conclusion, Cor modulated Ca2+ homeostasis by alleviating ERS and targeting NEDD4, thus mitigating apoptosis of RTECs in DKD. These findings indicate that Cor has the potential for the treatment and drug development of DKD.
Arginine vasopressin (AVP) is synthesised in magnocellular neurons (MCNs) of supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus. In response to the hyperosmotic stressors of dehydration (complete fluid deprivation, DH) or salt loading (drinking 2% salt solution, SL), AVP synthesis increases in MCNs, which over-burdens the protein folding machinery in the endoplasmic reticulum (ER). ER stress and the unfolded protein response (UPR) are signaling pathways that improve ER function in response to the accumulation of misfold/unfold protein. We asked whether an ER stress response was activated in the SON and PVN of DH and SL rats. We observed increased mRNA expression for the immunoglobulin heavy chain binding protein (BiP), activating transcription factor 4 (Atf4), C/EBP-homologous protein (Chop), and cAMP responsive element binding protein 3 like 1 (Creb3l1) in both SON and PVN of DH and SL rats. Although we found no changes in the splicing pattern of X box-binding protein 1 (Xbp1), an increase in the level of the unspliced form of Xbp1 (Xbp1U) was observed in DH and SL rats. CREB3L1, a novel ER stress inducer, has been shown to be activated by ER stress to regulate the expression of target genes. We have previously shown that CREB3L1 is a transcriptional regulator of the AVP gene; however, a role for CREB3L1 in the response to ER stress has yet to be investigated in MCNs. Here, we used lentiviral vectors to introduce a dominant negative form of CREB3L1 (CREB3L1DN) in the rat SON. Expression of CREB3L1DN in the SON decreased Chop and Xbp1U mRNA levels, but not BiP and Atf4 transcript expression. CREB3L1 is thus implicated as a transcriptional mediator of the ER stress response in the osmotically stimulated SON.
Epigallocatechin-3-gallate (EGCG) is the most abundant bioactive polyphenolic compound among the green tea constituents and has been identified as a potential anticancer agent in colorectal cancer (CRC) studies. This study was aimed to determine the mechanism of actions of EGCG when targeting the endoplasmic reticulum (ER) stress pathway in CRC. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay was performed on HT-29 cell line and normal cell line (3T3) to determine the EGCG toxicity. Next, western blot was done to observe the expression of the related proteins for the ER stress pathway. The Caspase 3/7 assay was performed to determine the apoptosis induced by EGCG. The results demonstrated that EGCG treatment was toxic to the HT-29 cell line. EGCG induced ER stress in HT-29 by upregulating immunoglobulin-binding (BiP), PKR-like endoplasmic reticulum kinase (PERK), phosphorylation of eukaryotic initiation factor 2 alpha subunit (eIF2α), activating transcription 4 (ATF4), and inositol-requiring kinase 1 alpha (IRE1α). Apoptosis was induced in HT-29 cells after the EGCG treatment, as shown by the Caspase 3/7 activity. This study indicates that green tea EGCG has the potential to inhibit colorectal cancer cells through the induction of ER stress.