Damaged deoxyribonucleic acid (DNA) is a primary pathologic factor for osteoarthritis (OA); however, the mechanism by which DNA damage drives OA is unclear. Previous research demonstrated that the ...cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) participates in DNA damage response. As a result, the current study aimed at exploring the role STING, which is the major effector in the cGAS-STING signaling casacde, in OA progress in vitro, as well as in vivo. In this study, the expression of STING was evaluated in the human and mouse OA tissues, and in chondrocytes exposed to interleukin-1 beta (IL-1β). The influences of STING on the metabolism of the extracellular matrix (ECM), apoptosis, and senescence, were assessed in STING overexpressing and knocking-down chondrocytes. Moreover, the NF-κB-signaling casacde and its role in the regulatory effects of STING on ECM metabolism, apoptosis, and senescence were explored. The STING knockdown lentivirus was intra-articularly injected to evaluate its therapeutic impact on OA in mice in vivo. The results showed that the expression of STING was remarkably elevated in the human and mouse OA tissues and in chondrocytes exposed to IL-1β. Overexpression of STING promoted the expression of MMP13, as well as ADAMTS5, but suppressed the expression of Aggrecan, as well as Collagen II; it also enhanced apoptosis and senescence in chondrocytes exposed to and those untreated with IL-1β. The mechanistic study showed that STING activated NF-κB signaling cascade, whereas the blockage of NF-κB signaling attenuated STING-induced apoptosis and senescence, and ameliorated STING-induced ECM metabolism imbalance. In in vivo study, it was demonstrated that STING knockdown alleviated destabilization of the medial meniscus-induced OA development in mice. In conclusion, STING promotes OA by activating the NF-κB signaling cascade, whereas suppression of STING may provide a novel approach for OA therapy.
The blockage of autophagic flux in chondrocytes has been considered as a major reason for the excessive cellular apoptosis and senescence in osteoarthritis (OA) development; however, the molecular ...mechanism and therapeutic strategy for interrupted autophagic flux is still not clear. Most recently, the transcription factor EB (TFEB) is identified as a master regulator for autophagic flux via initiating the expression of multiple autophagy-related genes and lysosomal biogenesis. This research was performed to confirm whether TFEB expression and activity are impacted in OA development and to confirm the effect of genetic up-regulation of TFEB on autophagic flux and cellular protection in the in vitro and in vivo models of OA. We demonstrated that the expression and nuclear localization of TFEB is decreased in human and mouse OA cartilage as well as in tert-Butyl hydroperoxide (TBHP)-treated chondrocytes. Applying lentivirus to transfect chondrocytes, we found that TFEB overexpression rescues the TBHP-induced the autophagic flux damage, lysosome dysfunction and protects chondrocyte against TBHP induced apoptosis and senescence; these protections of TFEB are diminished by chloroquine-medicated autophagy inhibition. Our destabilized medial meniscus (DMM) mouse OA model shows that TFEB overexpression ameliorates the surgery-induced cartilage degradation, restrains the apoptosis and senescence of chondrocyte, and enhances the autophagic flux. In summary, our study indicates that the activity of TFEB in chondrocyte is involved in OA development, also TFEB overexpression may be a promising strategy for OA treatment.
The pathophysiology of spinal cord injury (SCI) involves primary injury and secondary injury. Secondary injury is a major target for SCI therapy, whereas microglia play an important role in secondary ...injury. The immunoresponsive gene 1 (Irg-1) has been recorded as one of the most significantly upregulated genes in SCI tissues in gene chip data; however, its role in SCI remains unclear. This study aims to illustrate the role of Irg-1 as well as its regulated metabolite itaconate in SCI. It was demonstrated that the expression of Irg-1 was increased in spinal cord tissues in mice as well as in microglia stimulated by lipopolysaccharides (LPS). It was also shown that overexpression of Irg-1 may suppress LPS-induced inflammation in microglia, while these protective effects were attenuated by Nrf2 silencing. In vivo, overexpression of Irg-1 was shown to suppress neuroinflammation and improve motor function recovery. Furthermore, treatment of microglia with itaconate demonstrated similar inflammation suppressive effects as Irg-1 overexpression in vitro and improved motor function recovery in vivo. In conclusion, the current study shows that Irg-1 and itaconate are involved in the recovery process of SCI, either Irg-1 overexpression or itaconate treatment may provide a promising strategy for the treatment of SCI.
Spinal cord injury (SCI) is a severe neurological disease; however, few drugs have been proved to treat SCI effectively. Neuroinflammation is the major pathogenesis of SCI secondary injury and ...considered to be the therapeutic target of SCI. Salidroside (Sal) has been reported to exert anti‐inflammatory effects in airway, adipose and myocardial tissue; however, the role of Sal in SCI therapeutics has not been clarified. In this study, we showed that Sal could improve the functional recovery of spinal cord in rats as revealed by increased BBB locomotor rating scale, angle of incline, and decreased cavity of spinal cord injury and apoptosis of neurons in vivo. Immunofluorescence double staining of microglia marker and M1/M2 marker demonstrated that Sal could suppress M1 microglia polarization and activate M2 microglia polarization in vivo. To verify how Sal exerts its effects on microglia polarization and neuron protection, we performed the mechanism study in vitro in microglia cell line BV‐2 and neuron cell line PC12. The results showed that Sal prevents apoptosis of PC12 cells in coculture with LPS‐induced M1 BV‐2 microglia, also the inflammatory secretion phenotype of M1 BV‐2 microglia was suppressed by Sal, and further studies demonstrated that autophagic flux regulation through AMPK/mTOR pathway was involved in Sal regulated microglia polarization after SCI. Overall, our study illustrated that Sal could promote spinal cord injury functional recovery in rats, and the mechanism may relate to its microglia polarization modulation through AMPK‐/mTOR‐mediated autophagic flux stimulation.
Ribosomal DNA (rDNA) transcription drives cell growth and cell proliferation via the product ribosomal RNA (rRNA), the essential component of ribosome. Given the fundamental role of rRNA in ribosome ...biogenesis, rDNA transcription has emerged as one of the effective targets for a number of human diseases including various types of cancers. In this study, we identify curcumin, an ancient drug, as a novel natural inhibitor of rDNA transcription. Curcumin treatment impairs the assembly of the RNA polymerase I preinitiation complex at rDNA promoters and represses rDNA promoter activity, which leads to the decrease of rRNA synthesis. In addition, curcumin treatment stimulates autophagosome formation and promotes autophagic degradation in cells. Mechanistically, curcumin inactivates the mechanistic target of rapamycin complex 1 (mTORC1), the upstream regulator of rDNA transcription and autophagy induction, by inhibiting mTOR lysosomal localization. Functionally, curcumin treatment inhibits protein synthesis, cell growth and cell proliferation. Taken together, these findings identify curcumin as an effective inhibitor of rDNA transcription and provide novel mechanisms for the anticancer properties of curcumin.
Abbreviations:
Atg: autophagy-related; GFP: green fluorescent protein; LAMP2: lysosomal associated membrane protein 2; LC3: microtubule-associated protein 1 light chain 3; MEF: mouse embryonic fibroblast; mTORC1: mechanistic target of rapamycin complex 1; rDNA: ribosomal DNA; rRNA: ribosomal RNA; TP53INP2: tumor protein p53 inducible nuclear protein 2.
Diabetes (DB) is a risk factor for osteoarthritis progression. High glucose (HG) is one of the key pathological features of DB and has been demonstrated to induce apoptosis and senescence in ...chondrocytes. Autophagy is an endogenous mechanism that can protect cells against apoptosis and senescence. The effects of HG on autophagy in cells including chondrocytes have been studied; however, the results have been inconsistent. The current study aimed to elucidate the underlying mechanisms, which could be associated with the contrasting outcomes. The present study revealed that HG can induce apoptosis and senescence in chondrocytes, in addition to regulating autophagy dynamically. The present study demonstrated that HG can cause oxidative stress in chondrocytes and suppress the AMPK pathway in a dose-dependent manner. Elimination of oxidative stress by Acetylcysteine, also called N-acetyl cysteine (NAC), downregulated autophagy and alleviated HG-stimulated apoptosis and senescence, while activation of the AMPK signaling pathway by AICAR not only upregulated autophagy but also alleviated HG-stimulated apoptosis and senescence. A combined treatment of NAC and AICAR was superior to treatment with either NAC or AICAR. The study has demonstrated that HG can suppress autophagy through the AMPK pathway and induce autophagy via oxidative stress in chondrocytes.
Abstract Spinal cord injury (SCI) is a destructive neurological disorder that is characterized by impaired sensory and motor function. Inhibition of bromodomain protein 4 (Brd4) has been shown to ...promote the maintenance of cell homeostasis by activating autophagy. However, the role of Brd4 inhibition in SCI and the underlying mechanisms are poorly understood. Thus, the goal of the present study was to evaluate the effects of sustained Brd4 inhibition using the bromodomain and extraterminal domain (BET) inhibitor JQ1 on the regulation of apoptosis, oxidative stress and autophagy in a mouse model of SCI. First, we observed that Brd4 expression at the lesion sites of mouse spinal cords increased after SCI. Treatment with JQ1 significantly decreased the expression of Brd4 and improved functional recovery for up to 28 day after SCI. In addition, JQ1-mediated inhibition of Brd4 reduced oxidative stress and inhibited the expression of apoptotic proteins to promote neural survival. Our results also revealed that JQ1 treatment activated autophagy and restored autophagic flux, while the positive effects of JQ1 were abrogated by autophagy inhibitor 3-MA intervention, indicating that autophagy plays a crucial role in therapeutic effects Brd4 induced by inhibition of the functional recovery SCI. In the mechanistic analysis, we observed that modulation of the AMPK-mTOR-ULK1 pathway is involved in the activation of autophagy mediated by Brd4 inhibition. Taken together, the results of our investigation provides compelling evidence that Brd4 inhibition by JQ1 promotes functional recovery after SCI and that Brd4 may serve as a potential target for SCI treatment.
Low back pain, triggered by intervertebral disc degeneration (IVDD), is one of the most common causes of disability and financial expenditure worldwide. However, except for surgical interventions, ...effective medical treatment to prevent the progression of IVDD is lacking. This study aimed to investigate the effects of circKIF18A, a novel circRNA, on IVDD progression and to explore its underlying mechanism in IVDD. In this study, we found that oxidative stress was positively correlated with nucleus pulposus cell (NPC) senescence in IVDD and that circKIF18A was downregulated in IVDD and attenuated senescent phenotypes such as cell cycle arrest and extracellular matrix degradation in NPCs. Mechanistically, circKIF18A competitively suppressed ubiquitin-mediated proteasomal degradation of MCM7, and the protective effects of circKIF18A on NPCs were partially mediated by MCM7 under oxidative stress. Intradiscal injection of adenoviral circKIF18A ameliorated IVDD in a rat model. This study revealed that circKIF18A regulates NPC degeneration by stabilizing MCM7 and identified a novel signaling pathway, the circKIF18A-MCM7 axis, for anti-senescence molecular therapy in IVDD.
Osteoarthritis (OA) is a common degenerative joint disease featuring the degeneration, destruction, and ossification of cartilage. Inflammation which may facilitate OA occurrence and development is ...considered as the main pathological factor. Betulin, a natural product extracted from birch bark, has been commonly used for inflammation treatment; however, its role in OA remains unclear. This study is aimed to explore whether betulin can suppress IL-1β–induced inflammation in chondrocytes and alleviate OA
in vitro
and
in vivo
. In
in vitro
studies, the generation of pro-inflammatory factors, such as interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), prostaglandin E2 (PGE2), and nitric oxide (NO), was assessed using the enzyme-linked immunosorbent assay (ELISA) and Griess reaction. As revealed by results, betulin inhibited the expression of pro-inflammatory mediators. In addition, the protein expressions of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), matrix metalloproteinase (MMP-13), thrombospondin motifs 5 (ADAMTS5), Collagen II, and Aggrecan were quantified using Western blot analysis. We found that betulin could inhibit the generation of COX-2 and iNOS induced by IL-1β, indicating that betulin has anti-inflammatory effects in chondrocytes. Furthermore, betulin downregulates the expression of MMP-13 and ADAMTS-5 and upregulates the expression of Collagen II and Aggrecan, indicating that it can inhibit the degradation of the extracellular matrix. In mechanism, betulin activated the AKT/Nrf2 pathway and inhibited the phosphorylation of p65. In
in vivo
studies, administration of betulin
in vivo
could inhibit cartilage destruction and inflammatory progression. Therefore, these findings suggest that betulin may alleviate IL-1β–induced OA via the AKT/Nrf2/HO-1/NF-κB signal axis, and betulin may be a potential drug for the treatment of OA.
Oxidative stress-induced apoptosis and senescence of nucleus pulposus (NP) cells play a crucial role in the progression of intervertebral disc degeneration (IVDD). Accumulation of studies has shown ...that activated autophagy and enhanced autophagic flux can alleviate IVDD. In this study, we explored the effects of apigenin on IVDD
and
. Apigenin was found to inhibit tert-butyl hydroperoxide (TBHP)-induced apoptosis, senescence, and ECM degradation in NP cells. In addition, apigenin treatment can restore the autophagic flux blockage caused by TBHP. Mechanistically, we found that TBHP may induce autophagosome and lysosome fusion interruption and lysosomal dysfunction, while apigenin alleviates these phenomena by promoting the nuclear translocation of TFEB
the AMPK/mTOR signaling pathway. Furthermore, apigenin also exerts a protective effect against the progression of IVDD in the puncture-induced rat model. Taken together, these findings indicate that apigenin protects NP cells against TBHP-induced apoptosis, senescence, and ECM degradation
restoration of autophagic flux
, and it also ameliorates IVDD progression in rats
, demonstrating its potential for serving as an effective therapeutic agent for IVDD.
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