Histone hypo-acetylation of Sox9 mediates nicotine-induced weak cartilage repair by suppressing BMSC chondrogenic differentiation

α7nAChR activation in AT2 cells promotes alveolar regeneration through WNT7B signaling in acute lung injury

Reducing inflammatory damage and improving alveolar epithelium regeneration are two key approaches to promoting lung repair in acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Stimulation of cholinergic α7 nicotinic acetylcholine receptor (α7nAChR, coded by Chrna7) signaling could dampen lung inflammatory injury. However, whether activation of α7nAChR in alveolar type II (AT2) cells promotes alveolar epithelial injury repair and underlying mechanisms is elusive. Here, we found that α7nAChR was expressed on AT2 cells and was upregulated in response to LPS-induced ALI. Meanwhile, deletion of Chrna7 in AT2 cells impeded lung repair process and worsened lung inflammation in ALI. Using in vivo AT2 lineage-labeled mice and ex vivo AT2 cell-derived alveolar organoids, we demonstrated that activation of α7nAChR expressed on AT2 cells improved alveolar regeneration by promoting AT2 cells to proliferate and subsequently differentiate toward alveolar type I cells. Then, we screened out the WNT7B signaling pathway by the RNA-Seq analysis of in vivo AT2 lineage-labeled cells and further confirmed its indispensability for α7nAChR activation-mediated alveolar epithelial proliferation and differentiation. Thus, we have identified a potentially unrecognized pathway in which cholinergic α7nAChR signaling determines alveolar regeneration and repair, which might provide us a novel therapeutic target for combating ALI.

Acetylcholine Receptors in Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are well known for their regenerative potential. Even though the ability of MSCs to proliferate and differentiate has been studied extensively, there remains much to learn about the signaling mechanisms and pathways that control proliferation and influence the differentiation phenotype. In recent years, there has been growing evidence for the utility of non-neuronal cholinergic signaling systems and that acetylcholine (ACh) plays an important ubiquitous role in cell-to-cell communication. Indeed, cholinergic signaling is hypothesized to occur in stem cells and ACh synthesis, as well as in ACh receptor (AChR) expression, has been identified in several stem cell populations, including MSCs. Furthermore, AChRs have been found to influence MSC regenerative potential. In humans, there are two major classes of AChRs, muscarinic AChRs and nicotinic AChRs, with each class possessing several subtypes or subunits. In this review, the expression and function of AChRs in different types of MSC are summarized with the aim of highlighting how AChRs play a pivotal role in regulating MSC regenerative function.

Lithium-Containing Biomaterials Stimulate Cartilage Repair through Bone Marrow Stromal Cells-Derived Exosomal miR-455-3p and Histone H3 Acetylation

The repair of damaged cartilage still remains a great challenge in clinic. It is demonstrated that bone marrow stromal cells (BMSCs)-chondrocytes communication is of great significance for cartilage repair. Moreover, BMSCs have been confirmed to enhance biological function of chondrocytes via exosome-mediated paracrine pathway. Lithium-containing scaffolds have been reported to effectively promote cartilage regeneration; however, whether lithium-containing biomaterial could facilitate cartilage regeneration through regulating BMSCs-derived exosomes has not been illustrated. In the study, the model lithium-substituted bioglass ceramic (Li-BGC) is selected and regulatory effects of BMSCs-derived exosomes after Li-BGC treatment (Li-BGC-Exo) are systemically evaluated. The data reveal that Li-BGC-Exo notably promotes chondrogenesis, which attributes to the upregulated exosomal miR-455-3p transfer, consequently leads to suppression of histone deacetylase 2 (HDAC2) and enhanced histone H3 acetylation in chondrocytes. Notably, BMSCs-derived exosomes after LiCl treatment (LiCl-Exo) exhibits the similar regulatory effect with Li-BGC-Exo, indicating that the pro-chondrogenesis capability of them is mainly owing to the lithium ions. Furthermore, the in vivo study proves that LiCl-Exo remarkably facilitates cartilage regeneration. The research may provide novel possibility for the intrinsic mechanism of chondrogenesis trigged by lithium-containing biomaterials, and suggests that application of lithium-containing scaffolds may be a promising strategy for cartilage regeneration.

Cyclic Polypeptide D7 Protects Bone Marrow Mesenchymal Cells and Promotes Chondrogenesis during Osteonecrosis of the Femoral Head via Growth Differentiation Factor 15-Mediated Redox Signaling

Osteonecrosis of the femoral head (ONFH) is a debilitating disease that is closely associated with the clinical application of high-dose glucocorticoids. Elevated oxidative stress contributes to the pathophysiological changes observed in ONFH. The lack of effective treatments besides surgical intervention highlights the importance of finding novel therapeutics. Our previous studies demonstrated that D7, a cyclic polypeptide, enhances the adhesion, expansion, and proliferation of bone marrow mesenchymal stem cells (BMSCs). Therefore, in this study, we investigated the therapeutic effects of D7 against ONFH in BMSCs and evaluated the underlying mechanisms. First, we screened for ONFH risk factors. Then, we applied D7 treatment to steroid-induced ONFH (SONFH) in an in vitro model produced by dexamethasone (DEX) to further elucidate the underlying mechanisms. We found negative correlations among oxidative stress marker expression, growth differentiation factor 15 (GDF15) levels, and ONFH. Furthermore, we demonstrated that DEX inhibited the proliferation and induced apoptosis of BMSCs by suppressing GDF15/AKT/mammalian target of rapamycin (mTOR) signaling. D7 alleviated DEX-induced BMSCs injury and restored the chondrogenic function of BMSCs by activating GDF15/AKT/mTOR signaling. In addition, DEX-induced excessive reactive oxygen species (ROS) generation was an upstream trigger of GDF15-mediated signaling, and D7 ameliorated this DEX-induced redox imbalance by restoring the expression of antioxidants, including superoxide dismutase (SOD) 1, SOD2, and catalase, via regulation of GDF15 expression. In conclusion, our findings revealed the potential therapeutic effects of D7 in SONFH and showed that this protective function may be mediated via inhibition of DEX-induced ROS and activation of GDF15/AKT/mTOR signaling, thereby providing insights into the potential applications of D7 in SONFH treatment.

Nanog/NFATc1/Osterix signaling pathway-mediated promotion of bone formation at the tendon-bone interface after ACL reconstruction with De-BMSCs transplantation

Background

Bone formation plays an important role in early tendon–bone healing after anterior cruciate ligament reconstruction (ACLR). Dedifferentiated osteogenic bone marrow mesenchymal stem cells (De-BMSCs) have enhanced osteogenic potential. This study aimed to investigate the effect of De-BMSCs transplantation on the promotion of bone formation at the tendon–bone interface after ACLR and to further explore the molecular mechanism of the enhanced osteogenic potential of De-BMSCs.

Methods

BMSCs from the femurs and tibias of New Zealand white rabbits were subjected to osteogenic induction and then cultured in medium without osteogenic factors; the obtained cell population was termed De-BMSCs. De-BMSCs were induced to undergo osteo-, chondro- and adipo-differentiation in vitro to examine the characteristics of primitive stem cells. An ACLR model with a semitendinosus tendon was established in rabbits, and the animals were divided into a control group, BMSCs group, and De-BMSCs group. At 12 weeks after surgery, the rabbits in each group were sacrificed to evaluate tendon–bone healing by histologic staining, micro-computed tomography (micro-CT) examination, and biomechanical testing. During osteogenic differentiation of De-BMSCs, an siRNA targeting nuclear factor of activated T-cells 1 (NFATc1) was used to verify the molecular mechanism of the enhanced osteogenic potential of De-BMSCs.

Results

De-BMSCs exhibited some properties similar to BMSCs, including multiple differentiation potential and cell surface markers. Bone formation at the tendon–bone interface in the De-BMSCs group was significantly increased, and biomechanical strength was significantly improved. During the osteogenic differentiation of De-BMSCs, the expression of Nanog and NFATc1 was synergistically increased, which promoted the interaction of NFATc1 and Osterix, resulting in increased expression of osteoblast marker genes such as COL1A, OCN, and OPN.

Conclusions

De-BMSCs transplantation could promote bone formation at the tendon–bone interface after ACLR and improve the biomechanical strength of the reconstruction. The Nanog/NFATc1/Osterix signaling pathway mediated the enhanced osteogenic differentiation efficiency of De-BMSCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02643-9.

Histone Modifications and Chondrocyte Fate: Regulation and Therapeutic Implications

The involvement of histone modifications in cartilage development, pathology and regeneration is becoming increasingly evident. Understanding the molecular mechanisms and consequences of histone modification enzymes in cartilage development, homeostasis and pathology provides fundamental and precise perspectives to interpret the biological behavior of chondrocytes during skeletal development and the pathogenesis of various cartilage related diseases. Candidate molecules or drugs that target histone modifying proteins have shown promising therapeutic potential in the treatment of cartilage lesions associated with joint degeneration and other chondropathies. In this review, we summarized the advances in the understanding of histone modifications in the regulation of chondrocyte fate, cartilage development and pathology, particularly the molecular writers, erasers and readers involved. In addition, we have highlighted recent studies on the use of small molecules and drugs to manipulate histone signals to regulate chondrocyte functions or treat cartilage lesions, in particular osteoarthritis (OA), and discussed their potential therapeutic benefits and limitations in preventing articular cartilage degeneration or promoting its repair or regeneration.

The neuroprotective effects of activated α7 nicotinic acetylcholine receptor against mutant copper-zinc superoxide dismutase 1-mediated toxicity

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective and progressive loss of motor neurons. Although many drugs have entered clinical trials, few have shown effectiveness in the treatment of ALS. Other studies have shown that the stimulation of α7 nicotinic acetylcholine receptor (nAChR) can have neuroprotective effects in some models of neurodegenerative disease, as well as prevent glutamate-induced motor neuronal death. However, the effect of α7 nAChR agonists on ALS-associated mutant copper-zinc superoxide dismutase 1 (SOD1) aggregates in motor neurons remains unclear. In the present study, we examined whether α7 nAChR activation had a neuroprotective effect against SOD1^G85R-induced toxicity in a cellular model for ALS. We found that α7 nAChR activation by PNU282987, a selective agonist of α7 nAChR, exhibited significant neuroprotective effects against SOD1^G85R-induced toxicity via the reduction of intracellular protein aggregates. This reduction also correlated with the activation of autophagy through the AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) signaling pathway. Furthermore, the activation of α7 nAChRs was found to increase the biogenesis of lysosomes by inducing translocation of the transcription factor EB (TFEB) into the nucleus. These results support the therapeutic potential of α7 nAChR activation in diseases that are characterized by SOD1^G85R aggregates, such as ALS.

Association of Nicotine with Osteochondrogenesis and Osteoarthritis Development: The State of the Art of Preclinical Research

The deleterious effects of nicotine on various health conditions have been well documented. Although many orthopedic diseases are adversely affected by nicotine, little is known about its preclinical effects on chondrogenesis or osteogenesis, cartilage formation, osteoarthritis (OA), and osteochondral repair. A systematic review was conducted examining the current scientific evidence on the effects of nicotine on chondrogenesis or osteogenesis in vitro, possible consequences of prenatal nicotine exposure (PNE) on cartilage and OA susceptibility in the offspring, and whether nicotine affects OA development and osteochondral repair in vivo, always focusing on their underlying mechanisms. The data reveal dose-dependent effects on articular chondrocytes and on the chondrogenesis and osteogenesis of medicinal signaling cells in vitro, with lower doses often resulting in positive effects and higher doses causing negative effects. PNE negatively affects articular cartilage development and induces OA in the offspring without or with nicotine exposure. In contrast, protective effects on OA development were only reported in monosodium iodoacetate-induced small animal models. Finally, nicotine repressed MSC-based osteochondral repair in vivo. Future studies need to investigate dose-dependent clinical effects of smoking on cartilage quality in offspring, OA susceptibility and progression, and osteochondral repair more in detail, thus identifying possible thresholds for its pathological effects.

LncRNA HOXA-AS2 positively regulates osteogenesis of mesenchymal stem cells through inactivating NF-κB signalling

As is previously reported, mesenchymal stem cells have potential ability to differentiate into osteocytes. However, the underlying mechanism during this biological process is poorly understood. In the present study, we identify a novel long non-coding RNA named HOXA-AS2 as a critical regulator during the formation of osteogenesis. Attenuation of HOXA-AS2 can reduce the calcium deposition and repress the alkaline phosphatase activity. Moreover, the expressions of osteogenic marker genes are markedly downregulated after HOXA-AS2 depletion. Mechanistically, we found HOXA-AS2 can regulate the transcriptional activity of NF-κB, a critical inhibitor of osteogenesis. More importantly, HOXA-AS2 knockdown could result in the transcriptional repression of the osteogenic master transcription factor SP7 by a NF-κB/HDAC2-coordinated H3K27 deacetylation mechanism. Based on these studies, we conclude that HOXA-AS2 may serve as a promising therapeutic target for bone tissue repair and regeneration in the near future.