Glucocorticoid-induced autophagy and apoptosis in bone

PMAIP1 regulates autophagy in osteoblasts via the AMPK/mTOR pathway in osteoporosis

Osteoporosis (OP) is a highly prevalent disorder characterized by low bone mass that severely reduces patient quality of life. Although numerous treatments for OP have been introduced in clinic, many have side effects and high costs. Therefore, there is still an unmet need for optimal solutions. Here, raw signal analysis was used to identify potential high-risk factors for OP, and the biological functions and possible mechanisms of action (MOAs) of these factors were explored via gene set enrichment analysis (GSEA). Subsequently, molecular biological experiments were performed to verify and analyze the discovered risk factors in vitro and in vivo. PMAIP1 was identified as a potential risk factor for OP and significantly suppressed autophagy in osteoblasts via the AMPK/mTOR pathway, thereby inhibiting the proliferation and differentiation of osteoblasts. Furthermore, we constructed an ovariectomy (OVX) model of OP in rats and simultaneously applied si-PMAIP1 for in vivo interference. si-PMAIP1 upregulated the expression of LC3B and p-AMPK and downregulated the expression of p-mTOR, and these effects were reversed by the autophagy inhibitor. Micro-CT revealed that, si-PMAIP1 significantly inhibited the development of osteoporosis in OVX model rats, and this therapeutic effect was attenuated by treatment with an autophagy inhibitor. This study explored the role and mechanism of PMAIP1 in OP and demonstrated that PMAIP1 may serve as a novel target for OP treatment.

Global Trends in Research of Programmed Cell Death in Osteoporosis: A Bibliometric and Visualized Analysis (2000-2023)

Osteoporosis (OP) is a systemic metabolic bone disease that is characterized by decreased bone mineral density and microstructural damage to bone tissue. Recent studies have demonstrated significant advances in the research of programmed cell death (PCD) in OP. However, there is no bibliometric analysis in this research field. This study searched the Web of Science Core Collection (WoSCC) database for literature related to OP and PCD from 2000 to 2023. This study used VOSviewers 1.6.20, the "bibliometrix" R package, and CiteSpace (6.2.R3) for bibliometric and visualization analysis. A total of 2905 articles from 80 countries were included, with China and the United States leading the way. The number of publications related to PCD in OP is increasing year by year. The main research institutions are Shanghai Jiao Tong University, Chinese Medical University, Southern Medical University, Zhejiang University, and Soochow University. Bone is the most popular journal in the field of PCD in OP, and the Journal of Bone and Mineral Research is the most co-cited journal. These publications come from 14,801 authors, with Liu Zong-Ping, Yang Lei, Manolagas Stavros C, Zhang Wei, and Zhao Hong-Yan having published the most papers. Ronald S. Weinstein was co-cited most often. Oxidative stress and autophagy are the current research hot spots for PCD in OP. This bibliometric study provides the first comprehensive summary of trends and developments in PCD research in OP. This information identifies the most recent research frontiers and hot directions, which will provide a definitive reference for scholars studying PCD in OP.

Curcumin-loaded scaffolds in bone regeneration

In recent years, there has been a notable surge in the development of engineered bone scaffolds intended for the repair of bone defects. While autografts and allografts have traditionally served as the primary methods in bone tissue engineering, their inherent limitations have spurred the exploration of novel avenues in biomedical implant development. The emergence of bone scaffolds not only facilitates bone reconstruction but also offers a platform for the targeted delivery of therapeutic agents. There exists a pervasive interest in leveraging various drugs, proteins, growth factors, and biomolecules with osteogenic properties to augment bone formation, as the enduring side effects associated with current clinical modalities necessitate the pursuit of safer alternatives. Curcumin, the principal bioactive compound found in turmeric, has demonstrated notable efficacy in regulating the proliferation and differentiation of bone cells while promoting bone formation. Nevertheless, its utility is hindered by restricted water solubility and poor bioavailability. Strategies aimed at enhancing the solubility, stability, and bioavailability of curcumin, including formulation techniques such as liposomes and nanoparticles or its complexation with metals, have been explored. This investigation is dedicated to exploring the impact of curcumin on the proliferation, differentiation, and migration of osteocytes, osteoblasts, and osteoclasts.

Glycyrrhetinic Acid as a Hepatocyte Targeting Ligand-Functionalized Platinum(IV) Complexes for Hepatocellular Carcinoma Therapy and Overcoming Multidrug Resistance

Promising targeted therapy options to overcome drug resistance and side effects caused by platinum(II) drugs for treatment in hepatocellular carcinoma are urgently needed. Herein, six novel multifunctional platinum(IV) complexes through linking platinum(II) agents and glycyrrhetinic acid (GA) were designed and synthesized. Among them, complex 20 showed superior antitumor activity against tested cancer cells including cisplatin resistance cells than cisplatin and simultaneously displayed good liver-targeting ability. Moreover, complex 20 can significantly cause DNA damage and mitochondrial dysfunction, promote reactive oxygen species generation, activate endoplasmic reticulum stress, and eventually induce apoptosis. Additionally, complex 20 can effectively inhibit cell migration and invasion and trigger autophagy and ferroptosis in HepG-2 cells. More importantly, complex 20 demonstrated stronger tumor inhibition ability than cisplatin or the combo of cisplatin/GA with almost no systemic toxicity in HepG-2 or A549 xenograft models. Collectively, complex 20 could be developed as a potential anti-HCC agent for cancer treatment.

Alleviation of Glucocorticoid-Induced Osteoporosis in Rats by Ethanolic Reynoutria multiflora (Thunb.) Moldenke Extract

Secondary osteoporosis is frequently due to the use of high-dose glucocorticoids (GCs). The existing strategy for managing glucocorticoid-induced osteoporosis (GIOP) is considered insufficient and remains in a state of ongoing evolution. Therefore, it is crucial to develop more precise and effective agents for the treatment of GIOP. The constituents of Reynoutria multiflora (Thunb.) Moldenke, specifically Polygonum multiflorum (PM) Thunb, have previously shown promise in mitigating osteopenia. This study aimed to investigate the therapeutic effects of an ethanolic PM extract (PMR30) against GIOP in male rats. Prednisone (6 mg/kg/day, GC) was continuously administered to rats to induce GIOP, and they were subjected to treatment with or without ethanolic PMR30 for a duration of 120 days. Serum was collected for biochemical marker analysis. Bone histomorphometric, histological, and TUNEL analyses were performed on tibia samples. The protein expressions of LC3, Agt5, and Beclin 1 in the femur underwent examination through western blotting. Prolonged and excessive GC treatment significantly impeded bone formation, concomitant with reduced bone mass and body weight. It also suppressed OCN and OPG/RANKL in serum, and decreased Beclin 1 and LC3 in bone. Simultaneously, there was an elevation in bone resorption markers and apoptosis. Treatments with both high dose and low dose of PMR30 alleviated GIOP, stimulated bone formation, and upregulated OCN and OPG/RANKL, while suppressing TRACP-5b, CTX-I, and apoptosis. The impact of PMR30 possibly involves the enhancement of autophagy proteins (LC3, Agt5, and Beclin 1) and the inhibition of apoptosis within the bone. PMR30 holds promise as a prospective therapeutic agent for preventing and treating GIOP.

Integrated network pharmacology, molecular docking and pharmacodynamic study reveals protective effects and mechanisms of corilagin against cerebral ischemia-induced injury

BACKGROUND

Stroke is one of the leading causes of death and long-term disability worldwide. Previous studies have found that corilagin has antioxidant, anti-inflammatory, anti-atherosclerotic and other pharmacological activities and has a protective effect against cardiac and cerebrovascular injury.

OBJECTIVES

The aim of this study was to investigate the protective effects of corilagin against ischemic stroke and to elucidate the underlying molecular mechanisms using network pharmacology, molecular docking, and animal and cell experiments.

METHODS

We investigated the potential of corilagin to ameliorate cerebral ischemia-reperfusion injury using in vivo rat middle cerebral artery occlusion/reperfusion (MCAO/R) and in vitro oxygen-glucose deprivation/reoxygenation (OGD/R) models.

RESULTS

Our results suggest that corilagin may exert its anti-ischemic stroke effect by interacting with 92 key targets, including apoptosis-associated proteins (Bcl-2, Bax, caspase-3) and PI3K/Akt signaling pathway-related proteins. In vivo and in vitro experiments showed that corilagin treatment improved neurological deficits, attenuated cerebral infarct volume, and mitigated neuronal damage in MCAO/R rats. Corilagin treatment also enhanced the survival of PC12 cells exposed to OGD/R, reduced the rate of LDH leakage, inhibited cell apoptosis, and activated the PI3K/Akt signaling pathway. Importantly, the effects of corilagin on the PI3K/Akt signaling pathway and apoptosis-associated proteins were reversed by the PI3K-specific inhibitor LY294002.

CONCLUSIONS

These results indicate that the molecular mechanism of the anti-ischemic effect of corilagin involves inhibiting neuronal apoptosis and activating the PI3K/Akt signaling pathway. These findings provide a theoretical and experimental basis for the further development and application of corilagin as a potential anti-ischemic stroke agent.

Targeting proteostasis network in osteoporosis: Pathological mechanisms and therapeutic implications

As the most common bone disease, osteoporosis (OP) increases bone fragility and makes patients more vulnerable to the threat of osteoporotic fractures. With the ageing population in today's society, OP has become a huge and growing public health problem. Unfortunately, the clear pathogenesis of OP is still under exploration, and effective interventions are still scarce. Therefore, exploring new targets for pharmacological interventions to develop promising therapeutic drugs for OP is of great clinical value. Previous studies have shown that normal bone remodeling depends on proteostasis, whereas loss of proteostasis during ageing leads to the dysfunctional proteostasis network (PN) that fails to maintain bone homeostasis. Nevertheless, only a few studies have revealed the pathophysiological relationship between bone metabolism and a single component of PN, yet the role of PN as a whole in the pathogenesis of OP is still under investigation. This review comprehensively summarized the role of PN in the pathogenesis of OP and further discussed the potential of PN as innovative drug targets for the therapy of OP.

Pharmacological Interventions for Glucocorticoid-Induced Osteoporosis: An Umbrella Review

There is still a lack of high-quality evidence-based studies on the efficacy of drug treatment for glucocorticoid-induced osteoporosis (GIOP). The purpose of this umbrella review is to comprehensively evaluate the existing evidence to determine the efficacy and safety of pharmacological interventions for GIOP. We searched PubMed, Embase, and the Cochrane Library for systematic reviews and/or meta-analyses (SRs) of randomized controlled trials (RCTs) aimed at evaluating drug therapy for GIOP. Both the methodological quality and the strength of recommendation of the endpoints included in the SRs were evaluated by using the AMSTAR-2 tool and GRADE system, respectively. Six SRs involving 7225 GIOP patients in 59 RCTs were included in this umbrella review. The results of the methodological quality evaluation showed that 2 high-quality, 2 low-quality and 2 critically low-quality SRs were included. The GRADE evaluation results showed that the quality of evidence and the strength of recommendation of 46 outcome indicators were evaluated in the umbrella review; there were 3 with high-level evidence, 20 with moderate-level evidence, 15 with low-level evidence, and 8 with very low-level evidence. Moderate- to high-level evidence suggests that teriparatide, bisphosphonates, and denosumab can improve the bone mineral density in patients with GIOP. The findings of this umbrella review can enable patients and clinical healthcare professionals to choose the best drug prescription.

Low-dose dexamethasone promotes osteoblast viability by activating autophagy via the SGK1/FOXO3a signaling pathway

Autophagy contributes to bone homeostasis and development under physiological conditions. Although previous studies have demonstrated the induction of the autophagy machinery by endogenous glucocorticoids (GCs), the precise mechanisms involved have not yet been clarified. The current study aimed to explore the effect of a low dose of GC (10^-8 M dexamethasone, Dex) on autophagy in mouse embryonic osteoblastic precursor cells (MC3T3-E1 cells) and the potential mechanisms. The results showed that 10^-8 M Dex induced significant time-dependent increases in the expression and activation of serum- and glucocorticoid-induced kinase-1 (SGK1) in MC3T3-E1 cells and that these effects were accompanied by increased cell viability and decreased apoptosis. The autophagy inhibitor 3-MA significantly inhibited Dex-mediated promotion of viability. Moreover, Dex increased LC3II and Beclin-1 levels and decreased SQSTM/p62 levels in a time-dependent manner, and these effects were attenuated by pretreatment with 3-MA. Transfection of Dex-treated MC3T3-E1 cells with shRNA-SGK1 resulted in a significant reduction in cell viability and an increase in apoptosis. 3-MA further exacerbated these effects of SGK1 inhibition. Knocking down SGK1 before Dex exposure significantly reduced the phosphorylated forkhead box O3a (p-FOXO3a)/FOXO3 ratio, suppressed LC3II and Beclin-1 levels, and increased SQSTM/p62 levels in MC3T3-E1 cells, and these effects were amplified by 3-MA. In conclusion, the results revealed that low-dose GC treatment increased osteoblast viability by activating autophagy via the SGK1/FOXO3a pathway.

Mechanism of vascular endothelial cell-derived exosomes modified with vascular endothelial growth factor in steroid-induced femoral head necrosis

Steroid-induced avascular necrosis of the femoral head (SANFH) is an intractable orthopedic disease. This study investigated the regulatory effect and molecular mechanism of vascular endothelial cell (VEC)-derived exosomes (Exos) modified with vascular endothelial growth factor (VEGF) in osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in SANFH. VECs were culturedin vitroand transfected with adenovirus Adv-VEGF plasmids. Exos were extracted and identified.In vitro/vivoSANFH models were established and treated with VEGF-modified VEC-Exos (VEGF-VEC-Exos). The internalization of Exos by BMSCs, proliferation and osteogenic and adipogenic differentiation of BMSCs were determined by the uptake test, cell counting kit-8 (CCK-8) assay, alizarin red staining, and oil red O staining. Meanwhile, the mRNA level of VEGF, the appearance of the femoral head, and histological analysis were assessed by reverse transcription quantitative polymerase chain reaction and hematoxylin-eosin staining. Moreover, the protein levels of VEGF, osteogenic markers, adipogenic markers, and mitogen-activated protein kinase (MAPK)/extracellular regulated protein kinases (ERK) pathway-related indicators were examined by Western blotting, along with evaluation of the VEGF levels in femur tissues by immunohistochemistry. Glucocorticoid (GC) induced adipogenic differentiation of BMSCs and inhibited osteogenic differentiation. VEGF-VEC-Exos accelerated the osteogenic differentiation of GC-induced BMSCs and inhibited adipogenic differentiation. VEGF-VEC-Exos activated the MAPK/ERK pathway in GC-induced BMSCs. VEGF-VEC-Exos promoted osteoblast differentiation and suppressed adipogenic differentiation of BMSCs by activating the MAPK/ERK pathway. VEGF-VEC-Exos accelerated bone formation and restrained adipogenesis in SANFH rats. VEGF-VEC-Exos carried VEGF into BMSCs and motivated the MAPK/ERK pathway, thereby promoting osteoblast differentiation of BMSCs in SANFH, inhibiting adipogenic differentiation, and alleviating SANFH.

Interleukin 6 promotes BMP9-induced osteoblastic differentiation through Stat3/mTORC1 in mouse embryonic fibroblasts

Interleukin 6 (IL-6) plays a dual role in regulating bone metabolism, although the concrete mechanism is unclear. Bone morphogenetic protein 9 (BMP9) is one of the most potent osteogenic inducers, and a promising alternative for bone tissue engineering. The relationship between IL-6 and BMP9 in osteogenic differentiation remains to be elucidated, and the osteoblastic potential of BMP9 needs to be enhanced to overcome certain shortcomings of BMP9. In this study, we used real-time PCR, western blot, immunofluorescent stain, fetal limb culture and cranial defects repair model to explore the IL-6 role in BMP9-induced osteogenic differentiation in mouse embryonic fibroblasts (MEFs). We found that the rat serum level of IL-6 was increased in the dexamethasone-induced osteoporosis model, and IL-6 expression was detectable in several progenitor cells and MEFs. BMP9 upregulated IL-6 in MEFs, and the BMP9-induced osteoblastic markers were elevated by IL-6, but reduced by IL-6 knockdown. BMP9 and/or IL-6 both activated mTOR, and the IL-6 effect on BMP9-induced osteoblastic markers and bone formation were reduced greatly by mTOR inhibition. Raptor was up-regulated by IL-6 and/or BMP9 specifically, and the osteoblastic markers induced by IL-6 and/or BMP9 were reduced by Raptor knockdown. Meanwhile, Stat-3 was activated by IL-6 and/or BMP9, and the increase of Raptor or osteoblastic markers by IL-6 and/or BMP9 were reduced by Stat-3 inhibition. The Raptor promoter activity was regulated by p-Stat-3. Our finding suggested that IL-6 can promote the BMP9 osteoblastic potential, which may be mediated through activating Stat-3/mTORC1 pathway.

Cell death regulation: A new way for natural products to treat osteoporosis

Osteoporosis is a common metabolic bone disease that results from the imbalance of homeostasis within the bone. Intra-bone homeostasis is dependent on a precise dynamic balance between bone resorption by osteoclasts and bone formation by mesenchymal lineage osteoblasts, which comprises a series of complex and highly standardized steps. Programmed cell death (PCD) (e.g., apoptosis, autophagy, ferroptosis, pyroptosis, and necroptosis) is a cell death process that involves a cascade of gene expression events with tight structures. These events play a certain role in regulating bone metabolism by determining the fate of bone cells. Moreover, existing research has suggested that natural products derived from a wide variety of dietary components and medicinal plants modulate the PCDs based on different mechanisms, which show great potential for the prevention and treatment of osteoporosis, thus revealing the emergence of more acceptable complementary and alternative drugs with lower costs, fewer side effects and more long-term application. Accordingly, this review summarizes the common types of PCDs in the field of osteoporosis. Moreover, from the perspective of targeting PCDs, this review also discussed the roles of currently reported natural products in the treatment of osteoporosis and the involved mechanisms. Based on this, this review provides more insights into new molecular mechanisms of osteoporosis and provides a reference for developing more natural anti-osteoporosis drugs in the future.

Glucocorticoid induced bone disorders in children: Research progress in treatment mechanisms

Long-term or supra-physiological dose of glucocorticoid (GC) application in clinic can lead to impaired bone growth and osteoporosis. The side effects of GC on the skeletal system are particularly serious in growing children, potentially causing growth retardation or even osteoporotic fractures. Children's bone growth is dependent on endochondral ossification of growth plate chondrocytes, and excessive GC can hinder the development of growth plate and longitudinal bone growth. Despite the availability of drugs for treating osteoporosis, they have failed to effectively prevent or treat longitudinal bone growth and development disorders caused by GCs. As of now, there is no specific drug to mitigate these severe side effects. Traditional Chinese Medicine shows potential as an alternative to the current treatments by eliminating the side effects of GC. In summary, this article comprehensively reviews the research frontiers concerning growth and development disorders resulting from supra-physiological levels of GC and discusses the future research and treatment directions for optimizing steroid therapy. This article may also provide theoretical and experimental insight into the research and development of novel drugs to prevent GC-related side effects.

Autophagy: An important target for natural products in the treatment of bone metabolic diseases

Bone homeostasis depends on a precise dynamic balance between bone resorption and bone formation, involving a series of complex and highly regulated steps. Any imbalance in this process can cause disturbances in bone metabolism and lead to the development of many associated bone diseases. Autophagy, one of the fundamental pathways for the degradation and recycling of proteins and organelles, is a fundamental process that regulates cellular and organismal homeostasis. Importantly, basic levels of autophagy are present in all types of bone-associated cells. Due to the cyclic nature of autophagy and the ongoing bone metabolism processes, autophagy is considered a new participant in bone maintenance. Novel therapeutic targets have emerged as a result of new mechanisms, and bone metabolism can be controlled by interfering with autophagy by focusing on certain regulatory molecules in autophagy. In parallel, several studies have reported that various natural products exhibit a good potential to mediate autophagy for the treatment of metabolic bone diseases. Therefore, we briefly described the process of autophagy, emphasizing its function in different cell types involved in bone development and metabolism (including bone marrow mesenchymal stem cells, osteoblasts, osteocytes, chondrocytes, and osteoclasts), and also summarized research advances in natural product-mediated autophagy for the treatment of metabolic bone disease caused by dysfunction of these cells (including osteoporosis, rheumatoid joints, osteoarthritis, fracture nonunion/delayed union). The objective of the study was to identify the function that autophagy serves in metabolic bone disease and the effects, potential, and challenges of natural products for the treatment of these diseases by targeting autophagy.

A novel BMP2 secretagogue ameliorates glucocorticoid induced oxidative stress in osteoblasts by activating NRF2 dependent survival while promoting Wnt/β-catenin mediated osteogenesis

In our previous study, a novel BMP2 secretagogue was synthesized belonging to a class of galloyl conjugates of flavanones, with remarkable osteogenic potential that promoted bone regeneration. We aimed to establish the protective effect of our compound against bone loss that co-exists with excess Glucocorticoid (GC) therapy. GC therapy induces osteoblast damage leading to apoptosis by increasing reactive oxygen species (ROS). Our results delineate that compound 5e (a BMP2 secretagogue) activates NRF2 signalling to counter the disturbed cellular redox homeostasis and escalate osteoblast survival as assessed by Western blot and immunocytochemistry. Depletion of NRF2 by siRNA blocked activation of the NRF2/HO-1 pathway, magnified oxidative stress, increased apoptosis and abrogated the protective effects of compound 5e. 5e, on the other hand, increased ALP, mineralization activity, and promoted osteoblast differentiation by activating WNT/β-catenin signalling in BMP2 dependent manner, validated by Western blot of WNT3A, SOST, GSK3-β and β-catenin nuclear translocation. Treatment of 5e in presence of BMP inhibitor noggin attenuated the osteogenic efficacy and minimized Wnt//β-catenin signalling in presence of dexamethasone. Our compound prevents GC challenged trabecular and cortical bone loss assessed by micro-CT and promotes bone formation and osteocyte survival determined by calcein labelling and TUNEL assay in GC treated animals. The osteogenic potential of the compound was authenticated by bone turnover markers. On a concluding note, compounds with BMP upregulation can be potential therapeutics for the prevention and treatment of glucocorticoid-induced osteoporosis.

Autophagy: A Key Regulator of Homeostasis and Disease: An Overview of Molecular Mechanisms and Modulators

Autophagy is a highly conserved lysosomal degradation pathway active at basal levels in all cells. However, under stress conditions, such as a lack of nutrients or trophic factors, it works as a survival mechanism that allows the generation of metabolic precursors for the proper functioning of the cells until the nutrients are available. Neurons, as post-mitotic cells, depend largely on autophagy to maintain cell homeostasis to get rid of damaged and/or old organelles and misfolded or aggregated proteins. Therefore, the dysfunction of this process contributes to the pathologies of many human diseases. Furthermore, autophagy is highly active during differentiation and development. In this review, we describe the current knowledge of the different pathways, molecular mechanisms, factors that induce it, and the regulation of mammalian autophagy. We also discuss its relevant role in development and disease. Finally, here we summarize several investigations demonstrating that autophagic abnormalities have been considered the underlying reasons for many human diseases, including liver disease, cardiovascular, cerebrovascular diseases, neurodegenerative diseases, neoplastic diseases, cancers, and, more recently, infectious diseases, such as SARS-CoV-2 caused COVID-19 disease.

Bad to the Bone: The Effects of Therapeutic Glucocorticoids on Osteoblasts and Osteocytes

Despite the continued development of specialized immunosuppressive therapies in the form of monoclonal antibodies, glucocorticoids remain a mainstay in the treatment of rheumatological and auto-inflammatory disorders. Therapeutic glucocorticoids are unmatched in the breadth of their immunosuppressive properties and deliver their anti-inflammatory effects at unparalleled speed. However, long-term exposure to therapeutic doses of glucocorticoids decreases bone mass and increases the risk of fractures - particularly in the spine - thus limiting their clinical use. Due to the abundant expression of glucocorticoid receptors across all skeletal cell populations and their respective progenitors, therapeutic glucocorticoids affect skeletal quality through a plethora of cellular targets and molecular mechanisms. However, recent evidence from rodent studies, supported by clinical data, highlights the considerable role of cells of the osteoblast lineage in the pathogenesis of glucocorticoid-induced osteoporosis: it is now appreciated that cells of the osteoblast lineage are key targets of therapeutic glucocorticoids and have an outsized role in mediating their undesirable skeletal effects. As part of this article, we review the molecular mechanisms underpinning the detrimental effects of supraphysiological levels of glucocorticoids on cells of the osteoblast lineage including osteocytes and highlight the clinical implications of recent discoveries in the field.

Kidney Organoids as a Novel Platform to Evaluate Lipopolysaccharide-Induced Oxidative Stress and Apoptosis in Acute Kidney Injury

Sepsis-associated acute kidney injury (SA-AKI) is a life-threatening syndrome. Lipopolysaccharide (LPS) is a widely used inducer for modeling SA-AKI both in vivo and in vitro. However, due to the innate complexity of the kidney architecture, the mechanisms underlying the pathogenesis of SA-AKI, as well as those involved in LPS-induced kidney injury remain to be clarified. Kidney organoids derived from human pluripotent stem cells (hPSCs) act as a model of multiple types of kidney cells in vitro and eliminate potential confounders in vivo. In the current study, we established LPS-induced kidney injury models both in vivo and in human kidney organoids. Kidney function, pathological changes, and markers of oxidative stress were evaluated with/without the presence of methylprednisolone (MP) treatment both in vivo and in vitro. The extent of LPS-induced oxidative stress and apoptosis in kidney organoids was further investigated in vitro. LPS-induced acute kidney injury in mice, together with pathological changes and increased oxidative stress, as well as enhanced apoptosis in kidney cells were evaluated. These phenomena were ameliorated by MP treatment. Experiments in kidney organoids showed that the LPS-induced apoptotic effects occurred mainly in podocytes and proximal tubular cells. Our experiments demonstrated the efficacy of using kidney organoids as a solid platform to study LPS-induced kidney injury. LPS induced oxidative stress as well as apoptosis in kidney cells independently of changes in perfusion or immune cell infiltration. MP treatment partially alleviated LPS-induced injury by reducing kidney cell oxidative stress and apoptosis.

Antileukemic Effects of Anti-miR-146a, Anti-miR-155, Anti-miR-181a, and Prednisolone on Childhood Acute Lymphoblastic Leukemia

Prednisolone has been used frequently in the treatment of acute lymphoblastic leukemia. However, to overcome the challenges of the treatment, the development of additional therapies is of great importance. Small, non-protein-coding RNAs, namely, microRNAs (miRNAs), are critical epigenetic regulators with physiological and pathological importance. This study is aimed at determining the effects of miR-146a, miR-155, and miR-181a inhibition with their corresponding anti-miRs on both leukemic and healthy cells, individually and with prednisolone. Leukemic (SUP-B15) and healthy B-lymphocyte (NCI-BL 2171) cell lines were used in this study. A total of 12 experimental groups included individual and combinational silenced ALL-associated miRNAs (hsa-miR-155, hsa-miR-146a, and hsa-miR-181a) and their combination with prednisolone. Cytotoxicity, proliferation, cell cycle, and apoptosis analyses were performed by using WST-1, trypan blue, APC-BrdU, Annexin V, and JC-1 methods in each study group, respectively. To control the effectiveness of anti-miR transfection and prednisolone application, miRNA expression analysis was performed from all groups. Anti-miR application was effective on the viability, proliferation, cell cycle, and apoptosis of leukemia cells, and this effect was increased with prednisolone administration. In addition, this activity was found to be very low on healthy cells. In conclusion, anti-miR applications may have the potential for clinical use of adjuvant to or as an alternative to conventional therapies for childhood acute lymphoblastic leukemia.

Up-regulation of SIRT1 induced by 17beta-estradiol promotes autophagy and inhibits apoptosis in osteoblasts

Osteoporosis is a common systemic skeletal metabolism disorder resulting in bone fragility and increased fracture risk. Silent information regulator factor 2 homolog 1 (SIRT1) is crucial in the regulation of several biological processes, including bone metabolism, autophagy, apoptosis, and aging. This study aimed to assess whether the up-regulation of SIRT1 induced by 17beta-estradiol (17β-E2) could promote autophagy and inhibit apoptosis in osteoblasts via the AMPK-mTOR and FOXO3a pathways, respectively. The study found that 17β-E2 (10^-6 M) administration induced the up-regulation of SIRT1 in osteoblasts. Up-regulation of SIRT1 induced by 17β-E2 increased the expression level of LC3, Beclin-1, Bcl-2, p-AMPK, FOXO3a but decreased caspase-3 and p-mTOR expression, and then promoted autophagy and inhibited apoptosis. More autophagosomes were observed under a transmission electron microscope (TEM) in 17β-E2 and SRT1720 (a selective SIRT1 activator) co-treated group. When Ex527 (a SIRT1-specific inhibitor) was pretreated, the reversed changes were observed. Taken together, our findings demonstrated that the up-regulation of SIRT1 induced by 17β-E2 could promote autophagy via the AMPK-mTOR pathway and inhibit apoptosis via the FOXO3a activation in osteoblasts, and SIRT1 might become a more significant target in osteoporosis treatment.

A Neuroprotective Bovine Colostrum Attenuates Apoptosis in Dexamethasone-Treated MC3T3-E1 Osteoblastic Cells

Glucocorticoid-induced osteoporosis (GIO) is one of the most common secondary forms of osteoporosis. GIO is partially due to the apoptosis of osteoblasts and osteocytes. In addition, high doses of dexamethasone (DEX), a synthetic glucocorticoid receptor agonist, induces neurodegeneration by initiating inflammatory processes leading to neural apoptosis. Here, a neuroprotective bovine colostrum against glucocorticoid-induced neuronal damage was investigated for its anti-apoptotic activity in glucocorticoid-treated MC3T3-E1 osteoblastic cells. A model of apoptotic osteoblastic cells was developed by exposing MC3T3-E1 cells to DEX (0-700 μM). Colostrum co-treated with DEX was executed at 0.1-5.0 mg/mL. Cell viability was measured for all treatment schedules. Caspase-3 activation was assessed to determine both osteoblast apoptosis under DEX exposure and its potential prevention by colostrum co-treatment. Glutathione reduced (GSH) was measured to determine whether DEX-mediated oxidative stress-driven apoptosis is alleviated by colostrum co-treatment. Western blot was performed to determine the levels of p-ERK1/2, Bcl-XL, Bax, and Hsp70 proteins upon DEX or DEX plus colostrum exposure. Colostrum prevented the decrease in cell viability and the increase in caspase-3 activation and oxidative stress caused by DEX exposure. Cells, upon colostrum co-treated with DEX, exhibited higher levels of p-ERK1/2 and lower levels of Bcl-XL, Bax, and Hsp70. Our data support the notion that colostrum may be able to reduce DEX-induced apoptosis possibly via the activation of the ERK pathway and modulation of the Hsp70 system. We provided preliminary evidence on how bovine colostrum, as a complex and multi-component dairy product, in addition to its neuroprotective action, may affect osteoblastic cell survival undergoing apoptosis.

Enhanced autophagy suppresses inflammation-mediated bone loss through ROCK1 signaling in bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells (BMSCs) have strong proliferative ability and multi-directional differentiation potential. Osteoarthritis is a degenerative joint disease that is closely related to the loss of osteogenic differentiation function of BMSCs. Autophagy, plays a crucial role in the maintenance of cellular functions, but its regulatory mechanism during the osteogenic differentiation of BMSCs remains unclear. In this study, we analyzed the differential gene networks and pathways during BMSC osteogenesis using bioinformatics, and further validated the regulatory roles of autophagy during the osteogenic differentiation of BMSCs in inflammatory condition in vitro. We found that Tumor necrosis factor alpha (TNF-α) treatment led to actin cytoskeleton rearrangements and inhibited osteogenic differentiation in BMSCs. In addition, TNF-α enhanced Rho-associated protein kinase 1 (ROCK1) expression and decreased autophagy activation. ROCK1 knockdown reduced Endoplasmic Reticulum stress (ER stress) and promoted autophagy, resulting reversion of osteogenic differentiation in BMSCs under inflammatory condition. Rapamycin reversed the TNF-α-induced decrease in osteogenesis of BMSCs, assessed by alkaline phosphatase (ALP) activity and Alizarin staining. Autophagy treated with inhibitor 3-Methyladenine (3-MA) further increased TNF-α-induced osteogenesis inhibition of BMSCs. Collectively, these results indicate that ER stress and dysfunction of autophagy promote inflammation-induced bone loss through the activation of ROCK1 signaling in BMSCs.

Paeoniflorin Attenuates Dexamethasone-Induced Apoptosis of Osteoblast Cells and Promotes Bone Formation via Regulating AKT/mTOR/Autophagy Signaling Pathway

Paeoniflorin, a natural product derived from Paeonia lactiflora, possesses diverse pharmacological activities such as anti-inflammatory, antitumor, and antidiabetic effects. It has been reported for promoting osteoblastogenesis and inhibiting osteoclastogenesis. This study investigates the therapeutic effects of paeoniflorin in glucocorticoid-induced osteoporosis (GIOP) in vitro and in vivo. MC3T3-E1 cells were incubated with dexamethasone (DEX; 200 μM) and/or paeoniflorin (10 μM), followed by the investigation of cell proliferation, differentiation, mineralization, apoptosis, and autophagy. The AKT activator SC79 was used for evaluating the involvement of the AKT/mTOR signaling pathway. After DEX pretreatments, paeoniflorin promoted osteoblast differentiation and mineralization characterized by increase in Runx2, ALP, beclin-1, and LC3-II/LC3-I ratio levels and a decrease in apoptosis. The autophagy-promoting effects of paeoniflorin were reversed by SC79. C57BL/6 mice were given DEX (1 mg/kg) once daily and paeoniflorin (15 mg/kg) 48 hours for a total of 8 weeks followed by the investigation of histological changes, the trabecular bone microarchitecture, and the levels of bone turnover markers. The results showed that paeoniflorin increased alkaline phosphatase (ALP) activity and upregulated the expression of osteocalcin and beclin-1 but reduced the levels of Bax and C-terminal telopeptide of type I collagen (CTX-1). Thus, paeoniflorin may alleviate DEX-induced osteoporosis by promoting osteogenic differentiation and autophagy via inhibition of the AKT/mTOR signaling pathway.

Osteocyte apoptosis: the roles and key molecular mechanisms in resorption-related bone diseases

Vital osteocytes have been well known to function as an important orchestrator in the preservation of robustness and fidelity of the bone remodeling process. Nevertheless, some key pathological factors, such as sex steroid deficiency and excess glucocorticoids, and so on, are implicated in inducing a bulk of apoptotic osteocytes, subsequently resulting in resorption-related bone loss. As much, osteocyte apoptosis, under homeostatic conditions, is in an optimal state of balance tightly controlled by pro- and anti-apoptotic mechanism pathways. Importantly, there exist many essential signaling proteins in the process of osteocyte apoptosis, which has a crucial role in maintaining a homeostatic environment. While increasing in vitro and in vivo studies have established, in part, key signaling pathways and cross-talk mechanism on osteocyte apoptosis, intrinsic and complex mechanism underlying osteocyte apoptosis occurs in various states of pathologies remains ill-defined. In this review, we discuss not only essential pro- and anti-apoptotic signaling pathways and key biomarkers involved in these key mechanisms under different pathological agents, but also the pivotal role of apoptotic osteocytes in osteoclastogenesis-triggered bone loss, hopefully shedding new light on the attractive and proper actions of pharmacotherapeutics of targeting apoptosis and ensuing resorption-related bone diseases such as osteoporosis and fragility fractures.

Pinocembrin alleviates glucocorticoid-induced apoptosis by activating autophagy via suppressing the PI3K/Akt/mTOR pathway in osteocytes

Glucocorticoids are widely used in clinical practice, but are associated with potentially severe side effects like glucocorticoid-induced osteoporosis (GIOP) and glucocorticoid-associated osteonecrosis of the femoral head (GA-ONFH). Glucocorticoid-induced osteocyte apoptosis plays critical roles in the pathological processes of both GIOP and GA-ONFH. Pinocembrin is a natural flavonoid that may exert protective effects on osteocytes. The present study investigated the effects of pinocembrin on glucocorticoid-induced apoptosis of murine long bone osteocyte Y4 (MLO-Y4) cells and sought to elucidate the underlying molecular mechanism. We found that pinocembrin attenuated glucocorticoid-induced cell viability injury and apoptosis of MLO-Y4 cells. Moreover, pinocembrin increased Beclin-1 and LC3B-II level, but decreased p62 expression, suggesting that pinocembrin activates autophagy in glucocorticoid-treated MLO-Y4 cells. The protective effects of pinocembrin on glucocorticoid-induced apoptosis of MLO-Y4 cells were mimicked by a known stimulator of autophagy but prevented by a known inhibitor of autophagy. Pinocembrin also suppressed the PI3K/Akt/mTOR signaling pathway, which regulates cell autophagy, in glucocorticoid-treated MLO-Y4 cells. In conclusion, the results indicate that pinocembrin alleviates glucocorticoid-induced osteocyte apoptosis by activating autophagy via suppressing the PI3K/Akt/mTOR pathway. Pinocembrin may represent a potential natural agent for preventing and treating GIOP and GA-ONFH.

Biological Factors, Metals, and Biomaterials Regulating Osteogenesis through Autophagy

Bone loss raises great concern in numerous situations, such as ageing and many diseases and in both orthopedic and dentistry fields of application, with an extensive impact on health care. Therefore, it is crucial to understand the mechanisms and the determinants that can regulate osteogenesis and ensure bone balance. Autophagy is a well conserved lysosomal degradation pathway, which is known to be highly active during differentiation and development. This review provides a revision of the literature on all the exogen factors that can modulate osteogenesis through autophagy regulation. Metal ion exposition, mechanical stimuli, and biological factors, including hormones, nutrients, and metabolic conditions, were taken into consideration for their ability to tune osteogenic differentiation through autophagy. In addition, an exhaustive overview of biomaterials, both for orthopedic and dentistry applications, enhancing osteogenesis by modulation of the autophagic process is provided as well. Already investigated conditions regulating bone regeneration via autophagy need to be better understood for finely tailoring innovative therapeutic treatments and designing novel biomaterials.