The mitochondrial UPR induced by ATF5 attenuates intervertebral disc degeneration via cooperating with mitophagy.

Intervertebral disc degeneration (IVDD) is an aging disease that results in a low quality of life and heavy socioeconomic burden. The mitochondrial unfolded protein response (UPRmt) take part in various aging-related diseases. Our research intents to explore the role and underlying mechanism of UPRmt in IVDD. Nucleus pulposus (NP) cells were exposed to IL-1ß and nicotinamide riboside (NR) served as UPRmt inducer to treat NP cells. Detection of ATP, NAD + and NADH were used to determine the function of mitochondria. MRI, Safranin O-fast green and Immunohistochemical examination were used to determine the degree of IVDD in vivo. In this study, we discovered that UPRmt was increased markedly in the NP cells of human IVDD tissues than in healthy controls. In vitro, UPRmt and mitophagy levels were promoted in NP cells treated with IL-1ß. Upregulation of UPRmt by NR and Atf5 overexpression inhibited NP cell apoptosis and further improved mitophagy. Silencing of Pink1 reversed the protective effects of NR and inhibited mitophagy induced by the UPRmt. In vivo, NR might attenuate the degree of IDD by activating the UPRmt in rats. In summary, the UPRmt was involved in IVDD by regulating Pink1-induced mitophagy. Mitophagy induced by the UPRmt might be a latent treated target for IVDD.

Sesn2 Serves as a Regulator between Mitochondrial Unfolded Protein Response and Mitophagy in Intervertebral Disc Degeneration.

Mitochondrial unfold protein response (UPRmt) can induce mitophagy to protect cell from unfold protein. However, how UPRmt induces mitophagy to protect cell is not yet clear. Herein, Sesn2 was considered to be a key molecule that communicated UPRmt and mitophagy in the intervertebral disc. Silencing of Sesn2 was able to reverse the protective effects of Nicotinamide riboside (NR) on nucleus pulposus (NP) cells and inhibit mitophagy induced by UPRmt. UPRmt upregulated Sesn2 through Eif2ak4/eIF2α/Atf4, and further induced mitophagy. Sesn2 promoted the translocation of cytosolic Parkin and Sqstm1 to the defective mitochondria respectively, thereby enhancing mitophagy. The translocation of cytosolic Sqstm1 to the defective mitochondria was dependent on Parkin. The two functional domains of Sesn2 were necessary for the interaction of Sesn2 with Parkin and Sqstm1. The cytosolic interaction of Sesn2 between Parkin and Sqstm1 was independent on Pink1 (named as PINK1 in human) but the mitochondrial translocation was dependent on Pink1. Sesn2-/- mice showed a more severe degeneration and NR did not completely alleviate the intervertebral disc degeneration (IVDD) of Sesn2-/- mice. In conclusion, UPRmt could attenuate IVDD by upregulation of Sesn2-induced mitophagy. This study will help to further reveal the mechanism of Sesn2 regulating mitophagy, and open up new ideas for the prevention and treatment of IVDD.

Beraprost ameliorates postmenopausal osteoporosis by regulating Nedd4-induced Runx2 ubiquitination.

Bone health requires adequate bone mass, which is maintained by a critical balance between bone resorption and formation. In our study, we identified beraprost as a pivotal regulator of bone formation and resorption. The administration of beraprost promoted differentiation of mouse bone mesenchymal stem cells (M-BMSCs) through the PI3K-AKT pathway. In co-culture, osteoblasts stimulated with beraprost inhibited osteoclastogenesis in a rankl-dependent manner. Bone mass of p53 knockout mice remained stable, regardless of the administration of beraprost, indicating that p53 plays a vital role in the bone mass regulation by beraprost. Mechanistic in vitro studies showed that p53 binds to the promoter region of neuronal precursor cell-expressed developmentally downregulated 4 (Nedd4) to promote its transcription. As a ubiquitinating enzyme, Nedd4 binds to runt-related transcription factor 2 (Runx2), which results in its ubiquitination and subsequent degradation. These data indicate that the p53-Nedd4-Runx2 axis is an effective regulator of bone formation and highlight the potential of beraprost as a therapeutic drug for postmenopausal osteoporosis.

Exosomes derived from vascular endothelial cells antagonize glucocorticoid-induced osteoporosis by inhibiting ferritinophagy with resultant limited ferroptosis of osteoblasts.

High dose and long-term steroid treatment can alter antioxidative ability and decrease the viability and function of osteoblasts, leading to osteoporosis and osteonecrosis. Ferroptosis, a new type of cell death characterized by excessive lipid peroxidation due to the downregulation of GPX4 and system Xc- , is involved in glucocorticoid-induced osteoporosis. Endothelial cell-secreted exosomes (EC-Exos) are important mediators of cell-to-cell communication and are involved in many physiological and pathological processes. However, the effect of EC-Exos on osteoblasts exposed to glucocorticoids has not been reported. Here, we explored the role of EC-Exos in glucocorticoid-induced osteoporosis. In vivo and in vitro experiments indicated that EC-Exos reversed the glucocorticoid-induced osteogenic inhibition of osteoblasts by inhibiting ferritinophagy-dependent ferroptosis.

Vascular endothelial cell-secreted exosomes facilitate osteoarthritis pathogenesis by promoting chondrocyte apoptosis.

Exosomes are major mediators of cell-to-cell communication, and are involved in many physiological and pathological processes. Recently, the roles of exosomes in osteoarthritis (OA) and their therapeutic potential have received increasing attention. Exosomes derived from vascular endothelial cells have been confirmed to participate in the occurrence and development of numerous diseases; however, their effects in OA have not been reported. Here, we demonstrated the roles of exosomes secreted by vascular endothelial cells in the development of OA. Through in vivo and in vitro experiments, we demonstrated that exosomes derived from vascular endothelial cells decreased the ability of chondrocytes to resist oxidative stress by inhibiting autophagy and p21 expression, thereby increasing the cellular ROS content and inducing apoptosis. These findings indicate that exosomes derived from vascular endothelial cells promote the progression of OA, thus, providing new ideas for the diagnosis and treatment of OA.

Involvement of oxidative stress-induced annulus fibrosus cell and nucleus pulposus cell ferroptosis in intervertebral disc degeneration pathogenesis.

Ferroptosis is a necrotic form of regulated cell death that was associated with lipid peroxidation and free iron-mediated Fenton reactions. It has been reported that iron deficiency had been implicated in the pathogenesis of intervertebral disc degeneration (IVDD) by activating apoptosis. However, the role of ferroptosis in the process of IVDD has not been illuminated. Here, we demonstrate the involvement of ferroptosis in IVDD pathogenesis. Our in vitro models show the changes in protein levels of ferroptosis marker and enhanced lipid peroxidation level during oxidative stress. Safranin O staining, hematoxylin-eosin staining, and immunohistochemical were used to assess the IVDD after 8 weeks of surgical procedure in vivo. Treatment with ferrostatin-1, deferoxamine, and RSL3 demonstrate the role of ferroptosis in tert-butyl hydroperoxide (TBHP)-treated annulus fibrosus cells (AFCs) and nucleus pulposus cells (NPCs). Ferritinophagy, nuclear receptor coactivator 4 (NCOA4)-mediated ferritin selective autophagy, is originated during the process of ferroptosis in response to TBHP treatment. Knockdown and overexpression NCOA4 further prove TBHP may induce ferroptosis of AFCs and NPCs in an autophagy-dependent way. These findings support a role for oxidative stress-induced ferroptosis in the pathogenesis of IVDD.

NDUFA4L2 Regulated by HIF-1α Promotes Metastasis and Epithelial-Mesenchymal Transition of Osteosarcoma Cells Through Inhibiting ROS Production.

Osteosarcoma (OS) accounts for a large proportion of the types of bone tumors that are newly diagnosed, and is a relatively common bone tumor. However, there are still no effective treatments for this affliction. One interesting avenue is related to the mitochondrial NDUFA4L2 protein, which is encoded by the nuclear gene and is known to be a critical mediator in the regulation of cell survival. Thus, in this study, we aimed to investigate the effect of NDUFA4L2 upon the metastasis and epithelial-mesenchymal transition of OS. We found that NDUFA4L2 protein expression was upregulated in hypoxic conditions. We also used 2-ME and DMOG, which are HIF-1α inhibitors and agonists, respectively, to assess the effects related to decreasing or increasing HIF-1α expression. 2-ME caused a significant decrease of NDUFA4L2 expression and DMOG had the opposite effect. It was obvious that down-regulation of NDUFA4L2 had a direct interaction with the apoptosis of OS cells. Western blotting, wound healing analyses, Transwell invasion assays, and colony formation assays all indicated and supported the conclusion that NDUFA4L2 promoted OS cell migration, invasion, proliferation, and the epithelial-mesenchymal transition. During experiments, we incidentally discovered that autophagy and the ROS inhibitor could be used to facilitate the rescuing of tumor cells whose NDUFA4L2 was knocked down. Our findings will help to further elucidate the dynamics underlying the mechanism of OS cells and have provided a novel therapeutic target for the treatment of OS.

Characterization of LncRNA SNHG22 as a protector of NKIRAS2 through miR-4492 binding in osteosarcoma.

Many studies have revealed the function of long noncoding RNA (LncRNA) in regulating tumorigenesis of osteosarcoma (OS). As a subgroup of LncRNA, small nucleolar RNA host genes (SNHGs) have emerged as potentially important in OS. According to our recent findings, small nucleolar RNA host gene 22 (SNHG22) plays an important role in inhibiting the growth and metastasis of OS. However, the underlying mechanism of SNHG22 in regulating OS progression remains unknown. In this study, we confirmed that SNHG22 was downregulated in OS, and the overexpression of SNHG22 significantly inhibited OS progression in vivo and in vitro. Meanwhile, overexpression of SNHG22 also inhibited the migration and proliferation of human umbilical vein endothelial cells (HUVECs) and prevented the epithelial-to-mesenchymal transition (EMT) in OS. Furthermore, the interaction between miR-4492 and SNHG22 we previously predicted was validated by RNA pull-down assays and RNA immunoprecipitation assays. Dual-luciferase reporter assays showed that SNHG22 could directly interact with miR-4492 and upregulate the expression of NK-κB inhibitor-interacting Ras-like 2 (NKIRAS2) by its competing endogenous RNA (ceRNA) activity on miR-4492. In conclusion, our study has clarified the function of SNHG22 in OS progression and suggests a novel therapeutic target for OS.

Identification and Management of Paroxysmal Sympathetic Hyperactivity After Traumatic Brain Injury.

Paroxysmal sympathetic hyperactivity (PSH) has predominantly been described after traumatic brain injury (TBI), which is associated with hyperthermia, hypertension, tachycardia, tachypnea, diaphoresis, dystonia (hypertonia or spasticity), and even motor features such as extensor/flexion posturing. Despite the pathophysiology of PSH not being completely understood, most researchers gradually agree that PSH is driven by the loss of the inhibition of excitation in the sympathetic nervous system without parasympathetic involvement. Recently, advances in the clinical and diagnostic features of PSH in TBI patients have reached a broad clinical consensus in many neurology departments. These advances should provide a more unanimous foundation for the systematic research on this clinical syndrome and its clear management. Clinically, a great deal of attention has been paid to the definition and diagnostic criteria, epidemiology and pathophysiology, symptomatic treatment, and prevention and control of secondary brain injury of PSH in TBI patients. Potential benefits of treatment for PSH may result from the three main goals: eliminating predisposing causes, mitigating excessive sympathetic outflow, and supportive therapy. However, individual pathophysiological differences, therapeutic responses and outcomes, and precision medicine approaches to PSH management are varied and inconsistent between studies. Further, many potential therapeutic drugs might suppress manifestations of PSH in the process of TBI treatment. The purpose of this review is to present current and comprehensive studies of the identification of PSH after TBI in the early stage and provide a framework for symptomatic management of TBI patients with PSH.

Mitochondrial NDUFA4L2 attenuates the apoptosis of nucleus pulposus cells induced by oxidative stress via the inhibition of mitophagy.

The main pathological mechanism of intervertebral disc degeneration (IVDD) is the programmed apoptosis of nucleus pulposus (NP) cells. Oxidative stress is a significant cause of IVDD. Whether mitophagy is induced by strong oxidative stress in IVDD remains to be determined. This study aimed to investigate the relationship between oxidative stress and mitophagy and to better understand the mechanism of IVDD in vivo and in vitro. To this end, we obtained primary NP cells from the human NP and subsequently exposed them to TBHP. We observed that oxidative stress induced mitophagy to cause apoptosis in NP cells, and we suppressed mitophagy and found that NP cells were protected against apoptosis. Interestingly, TBHP resulted in mitophagy through the inhibition of the HIF-1α/NDUFA4L2 pathway. Therefore, the upregulation of mitochondrial NDUFA4L2 restricted mitophagy induced by oxidative stress. Furthermore, the expression levels of HIF-1α and NDUFA4L2 were decreased in human IVDD. In conclusion, these results demonstrated that the upregulation of NDUFA4L2 ameliorated the apoptosis of NP cells by repressing excessive mitophagy, which ultimately alleviated IVDD. These findings show for the first time that NDUFA4L2 and mitophagy may be potential therapeutic targets for IVDD.

PGC-1α acts as an mediator of Sirtuin2 to protect annulus fibrosus from apoptosis induced by oxidative stress through restraining mitophagy.

Apoptosis of annulus fibrosus (AF) is observed widely in intervertebral disc degeneration (IVDD) which causes weaken of tension in the annulus of intervertebral disc. Previous studies reported that apoptosis of AF is induced mainly by oxidative stress. SIRT2 is a major regulator of mitochondria to mediate ROS production. However, the mechanism of SIRT2 in IVDD remains unclear. Here, the expression of SIRT2 was detected in AF cells exposed to tert-Butyl hydroperoxide (TBHP) by western blotting. Autophagic flux and apoptosis were assessed by western blotting, flow cytometry and immunofluorescence respectively. Safranin O staining, HE, and immunohistochemical were used to assess the IVDD after 3, 6 and 9 months of surgical procedure in vivo. The expression of SIRT2 was decreased in AF cells treated with TBHP. Repression of mitophagy alleviated the apoptosis of AF cells caused by TBHP. Overexpression of PGC-1α prevented AF cells from apoptosis and mitophagy after applying Lenti-PGC-1α to transfect AF cells. These protections of PGC-1α were reduced by FCCP. Furthermore, the expression of PGC-1α was reduced and the level of mitophagy was increased in IVDD models. In conclusion, this study indicates that the regulation of PGC-1α expression provide a new theoretical basis for the mechanism of IVDD.

HIF-1α Regulates Glucocorticoid-Induced Osteoporosis Through PDK1/AKT/mTOR Signaling Pathway.

Long-term and high dose glucocorticoid treatment can cause decreased viability and function of osteoblasts, which leads to osteoporosis and osteonecrosis. In this study, we investigated the role and mechanism of action of HIF-1α in glucocorticoid-induced osteogenic inhibition in MC3T3-E1 cells. Our results showed that HIF-1α protein expression was reduced when MC3T3-E1 cells were exposed to dexamethasone (Dex) at varying concentrations ranging from 10-9 to 10-6 M. PDK1 expression was also decreased in MC3T3-E1 cells after dexamethasone treatment. MC3T3-E1 cells when treated with the glucocorticoid receptor antagonist RU486 along with dexamethasone showed enhanced HIF-1α expression. In addition, upregulated expression of HIF-1α was capable of promoting the osteogenic ability of MC3T3-E1 cells and PDK1 expression. However, the HIF-1α antagonist 2-methoxyestradiol (2-ME) had a reverse effect in MC3T3-E1 cells exposed to dexamethasone. Furthermore, the PDK1 antagonist dichloroacetate could repress the osteogenic ability of MC3T3-E1 cells, although HIF-1α was upregulated when transduced with adenovirus-HIF-1α construct. The PDK1 agonist PS48 was able to promote the osteogenic ability of MC3T3-E1 cells treated with dexamethasone. Importantly, the protein levels of p-AKT and p-mTOR were increased in MC3T3-E1 cells treated with dexamethasone after PS48 treatment. in vivo, the PDK1 agonist PS48 could maintain the bone mass of mice treated with dexamethasone. This study provides a new understanding of the mechanism of glucocorticoid-induced osteoporosis.

Palladium-Catalyzed Enantioselective Intramolecular Dearomative Heck Reaction.

Enantioselective intramolecular dearomative Heck reactions have been developed by Pd-catalyzed cross-coupling of aryl halides or aryl triflates with the internal C═C bond of indoles, benzofurans, pyrroles, and furans. A variety of structurally unique spiroheterocycles and benzofused heterocycles having N/O-substituted quaternary carbon stereocenters, and exocyclic olefin moieties were afforded in moderate to excellent yields with good to excellent enantioselectivities, showing a broad scope of the present protocol. A series of new BINOL- and H8-BINOL-based phosphoramidite ligands were synthesized and proved to be efficient chiral ligands in the reactions of C2-tethered substrates to form spiroheterocycles. ( S)-SEGPHOS turned out to be a good ligand for the reaction delivering benzofused indolines and pyrrolines. Synthetic applications based on transformations of the exocyclic double bonds were realized without loss of enantiopurities, including hydrogenation, hydroborylation, and stereospecific ring-expanding rearrangement.