Melatonin Protects Chronic Kidney Disease Mesenchymal Stem/Stromal Cells against Accumulation of Methylglyoxal via Modulation of Hexokinase-2 Expression.

Treatment options for patients with chronic kidney disease (CKD) are currently limited; therefore, there has been significant interest in applying mesenchymal stem/stromal cell (MSC)-based therapy to treat CKD. However, MSCs harvested from CKD patients tend to show diminished viability and proliferation due to sustained exposure to uremic toxins in the CKD environment, which limits their utility for cell therapy. The application of melatonin has been demonstrated to improve the therapeutic efficacy of MSCs derived from and engrafted to tissues in patients suffering from CKD, although the underlying biological mechanism has not been elucidated. In this study, we observed overexpression of hexokinase-2 (HK2) in serum samples of CKD patients and MSCs harvested from an adenine-fed CKD mouse model (CKD-mMSCs). HK2 upregulation led to increased production levels of methylglyoxal (MG), a toxic metabolic intermediate of abnormal glycolytic processes. The overabundance of HK2 and MG was associated with impaired mitochondrial function and low cell proliferation in CKD-mMSCs. Melatonin treatment inhibited the increases in HK2 and MG levels, and further improved mitochondrial function, glycolytic metabolism, and cell proliferation. Our findings suggest that identifying and characterizing metabolic regulators such as HK2 in CKD may improve the efficacy of MSCs for treating CKD and other kidney disorders.

Exosomes isolated from melatonin-stimulated mesenchymal stem cells improve kidney function by regulating inflammation and fibrosis in a chronic kidney disease mouse model.

Chronic kidney disease (CKD) is defined as structural and functional abnormalities of the kidney due to inflammation and fibrosis. We investigated the therapeutic effects of exosomes secreted by melatonin-stimulated mesenchymal stem cells (Exocue) on the functional recovery of the kidney in a CKD mouse model. Exocue upregulated gene expression of micro RNAs (miRNAs) associated with anti-inflammatory and anti-fibrotic effects. Exocue-treated groups exhibited low tumor necrosis factor-α and transforming growth factor-ß levels in serum and fibrosis inhibition in kidney tissues mediated through regulation of cell apoptosis and proliferation of fibrosis-related cells. Exocue treatment decreased the gene expression of CKD progression-related miRNAs. Moreover, the CKD severity was alleviated in the Exocue group via upregulation of aquaporin 2 and 5 levels and reduction of blood urea nitrogen and creatinine, resulting in functional recovery of the kidney. In conclusion, Exocue could be a novel therapeutic agent for treating CKD by regulating inflammation and fibrosis.

Melatonin Treatment Improves Renal Fibrosis via miR-4516/SIAH3/PINK1 Axis.

Dysregulation in mitophagy, in addition to contributing to imbalance in the mitochondrial dynamic, has been implicated in the development of renal fibrosis and progression of chronic kidney disease (CKD). However, the current understanding of the precise mechanisms behind the pathogenic loss of mitophagy remains unclear for developing cures for CKD. We found that miR-4516 is downregulated and its target SIAH3, an E3 ubiquitin protein ligase that reduces PINK1 accumulation to damaged mitochondria, is upregulated in the renal cortex of CKD mice. Here, we demonstrated that melatonin injection induces miR-4516 expression and suppresses SIAH3, and promotes PINK1/Parkin-mediated mitophagy. Furthermore, we demonstrated that melatonin injection attenuates the pathological features of CKD by improving mitochondrial homeostasis. Our data supports that mitochondrial autophagy regulation by activating miR-4516/SIAH3/PINK1 mitophagy signaling axis can be a viable new strategy for treating CKD.

PrPC Aptamer Conjugated-Gold Nanoparticles for Targeted Delivery of Doxorubicin to Colorectal Cancer Cells.

Anticancer drugs, such as fluorouracil (5-FU), oxaliplatin, and doxorubicin (Dox) are commonly used to treat colorectal cancer (CRC); however, owing to their low response rate and adverse effects, the development of efficient drug delivery systems (DDSs) is required. The cellular prion protein PrPC, which is a cell surface glycoprotein, has been demonstrated to be overexpressed in CRC, however, there has been no research on the development of PrPC-targeting DDSs for targeted drug delivery to CRC. In this study, PrPC aptamer (Apt)-conjugated gold nanoparticles (AuNPs) were synthesized for targeted delivery of Dox to CRC. Thiol-terminated PrPC-Apt was conjugated to AuNPs, followed by hybridization of its complementary DNA for drug loading. Finally, Dox was loaded onto the AuNPs to synthesize PrPC-Apt-functionalized doxorubicin-oligomer-AuNPs (PrPC-Apt DOA). The PrPC-Apt DOA were spherical nanoparticles with an average diameter of 20 nm. Treatment of CRC cells with PrPC-Apt DOA induced reactive oxygen species generation by decreasing catalase and superoxide dismutase activities. In addition, treatment with PrPC-Apt DOA inhibited mitochondrial functions by decreasing the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha, complex 4 activity, and oxygen consumption rates. Compared to free Dox, PrPC-Apt DOA decreased proliferation and increased apoptosis of CRC cells to a greater degree. In this study, we demonstrated that PrPC-Apt DOA targeting could effectively deliver Dox to CRC cells. PrPC-Apt DOA can be used as a treatment for CRC, and have the potential to replace existing anticancer drugs, such as 5-FU, oxaliplatin, and Dox.

Knockdown of CK2α reduces P-cresol-induced fibrosis in human renal proximal tubule epithelial cells via the downregulation of profilin-1.

Renal fibrosis is one of the main causes of chronic kidney disease. Many studies have focused on fibroblasts and myofibroblasts involved in renal fibrogenesis. Recently, several studies have reported that renal proximal tubule epithelial cells are possible initiators of renal fibrosis. However, the mechanism through which cells induce renal fibrosis is poorly understood. In this study, we found that CK2α induces fibrosis in renal proximal tubule epithelial cells (TH1) by regulating the expression of profilin-1 (Pfn1). CKD mouse model and TH1 cells treated with P-cresol also showed an increased level of Pfn1. The knockdown of CK2α suppressed fibrosis in TH1 cells via the downregulation of Pfn1. In particular, CK2α knockdown inhibited the expression of stress fibers and fibrosis-related proteins in P-cresol-treated TH1 cells. Furthermore, the knockdown of CK2α inhibited mitochondrial dysfunction and restored cellular senescence and cell cycle in P-cresol-treated TH1 cells. These results indicate that CK2α induces renal fibrosis through Pfn1, which makes CK2α a key target molecule in the treatment of fibrosis related to chronic kidney disease.

Role of PrPC in Cancer Stem Cell Characteristics and Drug Resistance in Colon Cancer Cells.

BACKGROUND/AIM: Cancer stem cell characteristics and drug resistance of colorectal cancer are associated with failure of cancer treatment. In this study, we investigated the effects of PrPC on cancer stem cell characteristics, migration, invasion, and drug resistance of 5FU-resistant CRC cells. MATERIALS AND METHODS: PrPC negative and PrPC positive cells were isolated from 5FU-resistant CRC cells using magnetic activated cell sorting. Sphere formation, cancer stem cell marker expression, migration, invasion, and drug resistance were analyzed. RESULTS: PrPC positive cells showed increased sphere formation capacity and increased expression of cancer stem cell markers compared to PrPC negative cells. In addition, PrPC positive cells showed increased migration, invasion and drug resistance compared to PrPC negative cells. Furthermore, knockdown of PrPC abolished these effects. CONCLUSION: PrPC expression is important in CRC cell behavior, such as sphere formation, migration, invasion, and drug resistance. PrPC is an important therapeutic target for the treatment of CRC.

Melatonin Suppresses Renal Cortical Fibrosis by Inhibiting Cytoskeleton Reorganization and Mitochondrial Dysfunction through Regulation of miR-4516.

Renal fibrosis, a major risk factor for kidney failure, can lead to chronic kidney disease (CKD) and is caused by cytoskeleton reorganization and mitochondrial dysfunction. In this study, we investigated the potential of melatonin treatment to reduce renal fibrosis by recovering the cytoskeleton reorganization and mitochondrial dysfunction. We found that miR-4516 expression was downregulated in the renal cortex of CKD mice and P-cresol-treated TH1 cells. Decreased miR-4516 expression stimulated cytoskeleton reorganization and mitochondrial dysfunction, and induced renal fibrosis. Melatonin treatment suppressed fibrosis by inhibiting cytoskeleton reorganization and restoring mitochondrial function via increased miR-4516 expression. More specifically, melatonin treatment increased miR-4516 expression while decreasing ITGA9 expression, thereby inhibiting cytoskeleton reorganization. In addition, increased expression of miR-4516 by melatonin treatment reduced ROS formation and restored mitochondrial function. These findings suggest that melatonin may be a promising treatment for patients with CKD having renal fibrosis. Moreover, regulation of miR-4516 expression may be a novel strategy for the treatment of renal fibrosis.

Melatonin Protects Human Renal Proximal Tubule Epithelial Cells Against High Glucose-Mediated Fibrosis via the Cellular Prion Protein-TGF-ß-Smad Signaling Axis.

Diabetes-mediated hyperglycemia is a major risk factor for renal fibrosis, resulting in the development of chronic kidney diseases. To address this issue, the effect of melatonin, which has an antioxidative potential, on renal fibrosis in human renal proximal tubule epithelial cells under high glucose conditions was investigated. Under high glucose conditions, the generation of reactive oxygen species was drastically increased in human renal proximal tubule epithelial cells, which lead to the inhibition of cell proliferation, enlargement of cell size, reduction of cell survival, and suppression of antioxidant enzyme activities. High glucose also increased the expression of transforming growth factor-ß, leading to an increase in Smad2 phosphorylation. These fibrotic phenotype changes increased the expression of fibrosis-mediated extracellular matrix proteins, such as fibronectin, collagen I, and α-smooth muscle actin. In addition, the level of cellular prion protein (PrPC), which is associated with several biological processes, was decreased by exposure to high glucose conditions. Melatonin recovered the expression levels of PrPC under high glucose conditions via phosphorylation of Akt, resulting in the prevention of high glucose-induced fibrosis. In particular, overexpression of PrPC blocked the high glucose-mediated fibrotic phenotype change. These findings indicate that melatonin could be a powerful agent for treating hyperglycemia-induced renal fibrosis.

Melatonin-stimulated exosomes enhance the regenerative potential of chronic kidney disease-derived mesenchymal stem/stromal cells via cellular prion proteins.

Chronic kidney disease (CKD) is caused by dysfunctional kidneys, which result in complications like cardiovascular diseases. Chronic kidney disease-induced pathophysiological conditions decrease efficacy of autologous mesenchymal stem/stromal cell (MSC)-based therapy by reducing MSC functionality. To enhance therapeutic potential in patients with CKD, we isolated exosomes derived from melatonin-treated healthy MSCs (MT exosomes) and assessed the biological functions of MT exosome-treated MSCs isolated from patients with CKD (CKD-MSCs). Treatment with melatonin increased the expression of cellular prion protein (PrPC ) in exosomes isolated from MSCs through the upregulation of miR-4516. Treatment with MT exosomes protected mitochondrial function, cellular senescence, and proliferative potential of CKD-MSCs. MT exosomes significantly increased the level of angiogenesis-associated proteins in CKD-MSCs. In a murine hindlimb ischemia model with CKD, MT exosome-treated CKD-MSCs improved functional recovery and vessel repair. These findings elucidate the regenerative potential of MT exosome-treated CKD-MSCs via the miR-4516-PrPC signaling axis. This study suggests that the treatment of CKD-MSCs with MT exosomes might be a powerful strategy for developing autologous MSC-based therapeutics for patients with CKD. Furthermore, miR-4516 and PrPC could be key molecules for enhancing the regenerative potential of MSCs in ischemic diseases.

Melatonin suppresses senescence-derived mitochondrial dysfunction in mesenchymal stem cells via the HSPA1L-mitophagy pathway.

Mesenchymal stem cells (MSCs) are a popular cell source for stem cell-based therapy. However, continuous ex vivo expansion to acquire large amounts of MSCs for clinical study induces replicative senescence, causing decreased therapeutic efficacy in MSCs. To address this issue, we investigated the effect of melatonin on replicative senescence in MSCs. In senescent MSCs (late passage), replicative senescence decreased mitophagy by inhibiting mitofission, resulting in the augmentation of mitochondrial dysfunction. Treatment with melatonin rescued replicative senescence by enhancing mitophagy and mitochondrial function through upregulation of heat shock 70 kDa protein 1L (HSPA1L). More specifically, we found that melatonin-induced HSPA1L binds to cellular prion protein (PrPC ), resulting in the recruitment of PrPC into the mitochondria. The HSPA1L-PrPC complex then binds to COX4IA, which is a mitochondrial complex IV protein, leading to an increase in mitochondrial membrane potential and anti-oxidant enzyme activity. These protective effects were blocked by knockdown of HSPA1L. In a murine hindlimb ischemia model, melatonin-treated senescent MSCs enhanced functional recovery by increasing blood flow perfusion, limb salvage, and neovascularization. This study, for the first time, suggests that melatonin protects MSCs against replicative senescence during ex vivo expansion for clinical application via mitochondrial quality control.

Protective Role of Fucoidan on Cisplatin-mediated ER Stress in Renal Proximal Tubule Epithelial Cells.

BACKGROUND/AIM: Administration of cisplatin in cancer patients is limited by the kidney-related adverse effects; however, a protective strategy is absent. We hypothesized that fucoidan protects the proximal tubule epithelial (TH-1) cells against the effects of cisplatin. MATERIALS AND METHODS: To assess the effect of fucoidan, its effect on reactive oxygen species (ROS) formation, endoplasmic reticulum (ER) stress response, DNA damage response (DDR), apoptosis, and cell-cycle arrest in TH-1 cells was investigated. RESULTS: Cisplatin increased the accumulation of ROS, leading to excessive ER stress. In presence of cisplatin, treatment of TH-1 cells with fucoidan significantly reduced the ER stress by maintaining the complex of GRP78 with PERK and IRE1α. In particular, fucoidan enhanced the antioxidative capacity through up-regulation of PrPC Furthermore, fucoidan suppressed cisplatin-induced apoptosis and cell-cycle arrest, whereas silencing of PRNP blocked these effects of fucoidan. CONCLUSION: Fucoidan may be a potential adjuvant therapy for cancer patients treated with cisplatin as it preserves renal functionality.

Melatonin Enhances Mitophagy by Upregulating Expression of Heat Shock 70 kDa Protein 1L in Human Mesenchymal Stem Cells under Oxidative Stress.

Human mesenchymal stem cells (hMSCs) are a potent source of cell-based regenerative therapeutics used to treat patients with ischemic disease. However, disease-induced oxidative stress disrupts mitochondrial homeostasis in transplanted hMSCs, resulting in hMSC apoptosis and reducing their efficacy post-transplantation. To address this issue, we evaluated the effects of melatonin on cellular defense mechanisms and mitophagy in hMSCs subjected to oxidative stress. H2O2-induced oxidative stress increases the levels of reactive oxygen species and reduces membrane potential in hMSCs, leading to mitochondrial dysfunction and cell death. Oxidative stress also decreases the expression of 70-kDa heat shock protein 1L (HSPA1L), a molecular chaperone that assists in the recruitment of parkin to the autophagosomal mitochondrial membrane. Decreased expression of HSPA1L destabilizes parkin, thereby impairing mitophagy. Our results indicate that treating hMSCs with melatonin significantly inhibited mitochondrial dysfunction induced by oxidative stress, which decreased hMSCs apoptosis. In damaged hMSCs, treatment with melatonin increased the levels of HSPA1L, which bound to parkin. The interaction between HSPA1L and parkin increased membrane potential and levels of oxidative phosphorylation, resulting in enhanced mitophagy. Our results indicate that melatonin increased the expression of HSPA1L, thereby upregulating mitophagy and prolonging cell survival under conditions of oxidative stress. In this study, we have shown that melatonin, a readily available compound, can be used to improve hMSC-based therapies for patients with pathologic conditions involving oxidative stress.

Pioglitazone Improves the Function of Human Mesenchymal Stem Cells in Chronic Kidney Disease Patients.

Mesenchymal stem cells (MSCs) are optimal sources of autologous stem cells for cell-based therapy in chronic kidney disease (CKD). However, CKD-associated pathophysiological conditions, such as endoplasmic reticulum (ER) stress and oxidative stress, decrease MSC function. In this work, we study the protective effect of pioglitazone on MSCs isolated from CKD patients (CKD-MSCs) against CKD-induced ER stress. In CKD-MSCs, ER stress is found to induce mitochondrial reactive oxygen species generation and mitochondrial dysfunction. Treatment with pioglitazone reduces the expression of ER stress markers and mitochondrial fusion proteins. Pioglitazone increases the expression of cellular prion protein (PrPC) in CKD-MSCs, which is dependent on the expression levels of proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). Treatment with pioglitazone is found to protect CKD-MSCs against reactive oxygen species generation, aberrant mitochondrial oxidative phosphorylation of complexes I and IV, and aberrant proliferation capacity through the PGC-1α-PrPC axis. These results indicate that pioglitazone protects the mitochondria of MSCs from CKD-induced ER stress. Pioglitazone treatment of CKD-MSCs may be a potential therapeutic strategy for CKD patients.

TUDCA-treated chronic kidney disease-derived hMSCs improve therapeutic efficacy in ischemic disease via PrPC.

Although autologous human mesenchymal stem cells (hMSCs) are a promising source for regenerative stem cell therapy in chronic kidney disease (CKD), the barriers associated with pathophysiological conditions limit therapeutic applicability to patients. We confirmed that level of cellular prion protein (PrPC) in serum was decreased and mitochondria function of CKD-derived hMSCs (CKD-hMSCs) was impaired in patients with CKD. We proved that treatment of CKD-hMSCs with tauroursodeoxycholic acid (TUDCA), a bile acid, enhanced the mitochondrial function of these cells through regulation of PINK1-PrPC-dependent pathway. In a murine hindlimb ischemia model with CKD, tail vein injection of TUDCA-treated CKD-hMSCs improved the functional recovery, including kidney recovery, limb salvage, blood perfusion ratio, and vessel formation along with restored expression of PrPC in the blood serum of the mice. These data suggest that TUDCA-treated CKD-hMSCs are a promising new autologous stem cell therapeutic intervention that dually treats cardiovascular problems and CKD in patients.

TUDCA-Treated Mesenchymal Stem Cells Protect against ER Stress in the Hippocampus of a Murine Chronic Kidney Disease Model.

Chronic kidney disease (CKD) leads to the loss of kidney function, as well as the dysfunction of several other organs due to the release of uremic toxins into the system. In a murine CKD model, reactive oxygen species (ROS) generation and endoplasmic reticulum (ER) stress are increased in the hippocampus. Mesenchymal stem cells (MSCs) are one of the candidates for cell-based therapy for CKD; however severe pathophysiological conditions can decrease their therapeutic potential. To address these issues, we established tauroursodeoxycholic acid (TUDCA)-treated MSCs using MSCs isolated from patients with CKD (CKD-hMSCs) and assessed the survival and ROS generation of neural cell line SH-SY5Y cells by co-culturing with TUDCA-treated CKD-hMSCs. In the presence of the uremic toxin P-cresol, the death of SH-SY5Y cells was induced by ROS-mediated ER stress. Co-culture with TUDCA-treated CKD-hMSCs increased anti-oxidant enzyme activities in SH-SY5Y cells through the upregulation of the cellular prion protein (PrPC) expression. Upregulated PrPC expression in SH-SY5Y cells protected against CKD-mediated ER stress and apoptosis. In an adenine-induced murine CKD model, injection with TUDCA-treated CKD-hMSCs suppressed ROS generation and ER stress in the hippocampus. These results indicate that TUDCA-treated CKD-hMSCs prevent the CKD-mediated cell death of SH-SY5Y cells by inhibiting ER stress. Our study suggests that treatment with TUDCA could be a powerful strategy for developing autologous MSC-based therapeutics for patients with CKD, and that PrPC might be a pivotal target for protecting neural cells from CKD-mediated ER stress.

Melatonin protects mesenchymal stem cells from autophagy-mediated death under ischaemic ER-stress conditions by increasing prion protein expression.

OBJECT: The purpose of this study was to explore whether melatonin could protect mesenchymal stem cells (MSCs) against ischaemic injury, by inhibiting endoplasmic reticulum (ER) stress and autophagy both in vivo and in vitro. MATERIALS AND METHODS: To confirm the protective effect of melatonin against ER stress in MSCs, markers of cell viability, apoptosis and autophagy were analysed. To further investigate the regenerative effect of melatonin-treated MSCs in ischaemic tissues, a murine hindlimb ischaemic model was established. RESULTS: Under oxidative stress conditions, treatment with melatonin suppressed the activation of ER stress-associated proteins and autophagy-associated proteins acting through upregulation of cellular prion protein (PrPC ) expression. Consequently, inhibition of apoptotic cell death occurred. Melatonin also promoted the activation of MnSOD and catalase activities in MSCs. In a murine hindlimb ischaemia model, melatonin-treated MSCs also enhanced the functional limb recovery as well as neovascularization. These beneficial effects of melatonin were all blocked by knock-down of PrPC expression. CONCLUSION: Melatonin protects against ER stress/autophagy-induced apoptotic cell death by augmenting PrPC expression. Thus, melatonin-treated MSCs could be a potential cell-based therapeutic agent for ER stress-induced ischaemic diseases, and melatonin-induced PrPC might be a key molecule in ameliorating ER stress and autophagy.

Pioglitazone Protects Mesenchymal Stem Cells against P-Cresol-Induced Mitochondrial Dysfunction via Up-Regulation of PINK-1.

Mesenchymal stem cells (MSC) could be a candidate for cell-based therapy in chronic kidney disease (CKD); however, the uremic toxin in patients with CKD restricts the therapeutic efficacy of MSCs. To address this problem, we explored the effect of pioglitazone as a measure against exposure to the uremic toxin P-cresol (PC) in MSCs. Under PC exposure conditions, apoptosis of MSCs was induced, as well as PC-induced dysfunction of mitochondria by augmentation of mitofusion, reduction of mitophagy, and inactivation of mitochondrial complexes I and IV. Treatment of MSCs with pioglitazone significantly inhibited PC-induced apoptosis. Pioglitazone also prevented PC-induced mitofusion and increased mitophagy against PC exposure through up-regulation of phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK-1). Furthermore, pioglitazone protected against PC-induced mitochondrial dysfunction by increasing the cytochrome c oxidase subunit 4 (COX4) level and activating complexes I and IV, resulting in enhancement of proliferation. In particular, activation of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) regulated the pioglitazone-mediated up-regulation of PINK-1. These results indicate that pioglitazone protects MSCs against PC-induced accumulated mitochondrial dysfunction via the NF-κB⁻PINK-1 axis under P-cresol exposure conditions. Our study suggests that pioglitazone-treated MSCs could be a candidate for MSC-based therapy in patients with CKD.

Melatonin Promotes Apoptosis of Oxaliplatin-resistant Colorectal Cancer Cells Through Inhibition of Cellular Prion Protein.

BACKGROUND/AIM: Drug resistance restricts the efficacy of chemotherapy in colorectal cancer. However, the detailed molecular mechanism of drug resistance in colorectal cancer cells remains unclear. MATERIALS AND METHODS: The level of cellular prion protein (PrPC) in oxaliplatin-resistant colorectal cancer (SNU-C5/Oxal-R) cells was assessed. RESULTS: PrPC level in SNU-C5/Oxal-R cells was significantly increased compared to that in wild-type (SNU-C5) cells. Superoxide dismutase and catalase activities were higher in SNU-C5/Oxal-R cells than in SNU-C5 cells. Treatment of SNU-C5/Oxal-R cells with oxaliplatin and melatonin reduced PrPC expression, while suppressing antioxidant enzyme activity and increasing superoxide anion generation. In SNU-C5/Oxal-R cells, endoplasmic reticulum stress and apoptosis were significantly increased following co-treatment with oxaliplatin and melatonin compared to treatment with oxaliplatin alone. CONCLUSION: Co-treatment with oxaliplatin and melatonin increased endoplasmic reticulum stress in and apoptosis of SNU-C5/Oxal-R cells through inhibition of PrPC, suggesting that PrPC could be a key molecule in oxaliplatin resistance of colorectal cancer cells.

Tauroursodeoxycholic Acid Protects against the Effects of P-Cresol-Induced Reactive Oxygen Species via the Expression of Cellular Prion Protein.

Mesenchymal stem cells (MSCs) could be a promising solution in the treatment of various diseases including chronic kidney disease (CKD). However, endoplasmic reticulum (ER) stress induced by ischemia in the area of application limits the integration and survival of MSCs in patients. In our study, we generated ER stress-induced conditions in MSCs using P-cresol. As P-cresol is a toxic compound accumulated in the body of CKD patients and induces apoptosis and inflammation through reactive oxygen species (ROS), we observed ER stress-induced MSC apoptosis activated by oxidative stress, which in turn resulted from ROS generation. To overcome stress-induced apoptosis, we investigated the protective effects of tauroursodeoxycholic acid (TUDCA), a bile acid, on ER stress in MSCs. In ER stress, TUDCA treatment of MSCs reduced ER stress-associated protein activation, including GRP78, PERK, eIF2α, ATF4, IRE1α, and CHOP. Next, to explore the protective mechanism adopted by TUDCA, TUDCA-mediated cellular prion protein (PrPC) activation was assessed. We confirmed that PrPC expression significantly increased ROS, which was eliminated by superoxide dismutase and catalase in MSCs. These findings suggest that TUDCA protects from inflammation and apoptosis in ER stress via PrPC expression. Our study demonstrates that TUDCA protects MSCs against inflammation and apoptosis in ER stress by PrPC expression in response to P-cresol exposure.

Role of hypoxia­mediated cellular prion protein functional change in stem cells and potential application in angiogenesis (Review).

Cellular prion protein (PrPC) can replace other pivotal molecules due to its interaction with several partners in performing a variety of important biological functions that may differ between embryonic and mature stem cells. Recent studies have revealed major advances in elucidating the putative role of PrPC in the regulation of stem cells and its application in stem cell therapy. What is special about PrPC is that its expression may be regulated by hypoxia­inducible factor (HIF)­1α, which is the transcriptional factor of cellular response to hypoxia. Hypoxic conditions have been known to drive cellular responses that can enhance cell survival, differentiation and angiogenesis through adaptive processes. Our group recently reported hypoxia­enhanced vascular repair of endothelial colony­forming cells on ischemic injury. Hypoxia­induced AKT/signal transducer and activator of transcription 3 phosphorylation eventually increases neovasculogenesis. In stem cell biology, hypoxia promotes the expression of growth factors. According to other studies, aspects of tissue regeneration and cell function are influenced by hypoxia, which serves an essential role in stem cell HIF­1α signaling. All these data suggest the possibility that hypoxia­mediated PrPC serves an important role in angiogenesis. Therefore, the present review summarizes the characteristics of PrPC, which is produced by HIF­1α in hypoxia, as it relates to angiogenesis.