Inhibition of SIRT1 by miR-138-5p provides a mechanism for inhibiting osteoblast proliferation and promoting apoptosis under simulated microgravity

Mechanisms of pyroptosis in modulating osteoblast function under simulated microgravity

BACKGROUND

Bone mass loss resulting from mechanical unloading in a microgravity environment constitutes a primary impediment to the advancement of space exploration for astronauts. However, the underlying mechanism remains unclear. In this study, we primarily investigated the impact of pyroptosis on osteoblasts under simulated microgravity and its influence on osteoblast functionality.

METHODS

A rotary cell culture system was employed to establish a simulated microgravity environment. The proliferation of osteoblasts was assessed by cell counting kit-8 (CCK-8) assay. Lactate dehydrogenase (LDH) Release Assay Kit was used to measure cell necrosis. Osteoblast differentiation and mineralization were evaluated using an ALP kit and alizarin red staining. Fluorescence Hoechst/PI double staining and scanning electron microscopy (SEM) were used to detect pyroptosis, and a caspase-1 kit measured caspase-1 activity. The expression of NLRP3, caspase-1, GSDMD, IL-1β, IL-18, OCN, and COL-I was analyzed by qPCR and Western blot. Additionally, ELISA was used to quantify the release of IL-1β and IL-18.

RESULTS

The PI fluorescence in osteoblasts exhibited significant enhancement under simulated microgravity conditions, accompanied by increased membrane pore formation, decreased cell proliferation, and elevated LDH release. Moreover, the expression levels of NLRP3, caspase-1, GSDMD, IL-1β, and IL-18 were upregulated while caspase-1 activity was increased. Treatment with MCC950 and VX-765 effectively attenuated pyroptosis levels as well as caspase-1 activity while reducing the expression of NLRP3, GSDMD, IL-1β, and IL-18. Notably, this treatment significantly enhanced the expression of OCN and COL-I.

CONCLUSION

Under simulated microgravity conditions, pyroptosis occurs in osteoblasts and alters their osteogenic differentiation function. Pyroptosis modulates the functionality of osteoblasts and contributes to the mechanical response process, potentially serving as one of the mechanisms underlying mechanical-regulated osteoblast function in a microgravity environment. This finding may offer a novel approach for addressing bone tissue damage and repair under extreme mechanical conditions.

CLINICAL TRIAL NUMBER

Not applicable.

Enhancing Osteoblast Activity and Accelerating Fracture Healing via miR-656-3p Downregulation: A Novel Targeting Strategy Focused on BMP-2 Expression

Delayed fracture healing (DFH), a common complication of post-fracture surgery, exhibits an incompletely understood pathogenesis. The present study endeavors to investigate the roles and underlying mechanisms of miR-656-3p and Bone Morphogenetic Protein-2 (BMP-2) in DFH. It was recruited 94 patients with normal fracture healing (NFH) and 88 patients with DFH of the femoral neck. Serum miR-656-3p and BMP-2 expressions were quantified using RT-qPCR and the diagnostic potential of them for DFH was evaluated using ROC analysis. Factors influencing fracture healing were identified through logistic regression analysis. Osteogenic differentiation of MC3T3-E1 cells was induced, followed by evaluations of cell proliferation, apoptosis, and differentiation capabilities utilizing CCK-8, flow cytometry, and mRNA expression analysis of osteogenic markers. The targeting relationship between miR-656-3p and BMP-2 was validated through luciferase reporter assays. The levels of miR-656-3p were significantly elevated in DFH patients compared to those with NFH, whereas BMP-2 levels exhibited a decrease, a negative correlation between their expression patterns. Logistic regression analysis revealed that miR-656-3p and BMP-2 serve as influential factors in fracture healing, with their combined assessment exhibiting enhanced predictive value for DFH. Downregulation of miR-656-3p promoted proliferation and differentiation of MC3T3-E1 cells while inhibiting apoptosis. BMP-2, identified as a target of miR-656-3p, negated the effects of miR-656-3p downregulation when BMP-2 expression was inhibited. miR-656-3p modulates osteoblast function by targeting BMP-2, offering novel therapeutic and diagnostic targets for the management of DFH.

Recent progresses on space life science research in China

In the past decades, China has made significant progress on space life science research. Since completing the construction of the China Space Station (CSS) at the end of 2022, space life science research in China has entered a new era. Through carrying out numerous experiments on space life sciences, space medicine, and space agriculture conducted aboard the Shenzhou series, the CSS, and ground-based space environment simulation platforms, Chinese scientists have uncovered the effects of the space environment on the physiological and molecular mechanisms of live organisms. These findings provide essential theoretical support for long-term manned space exploration. In this article, we review the new discoveries made by Chinese researchers, focusing on the impacts of both actual and simulated space environment on cells, microorganisms, plants, animals, and human health.

Omics Studies of Tumor Cells under Microgravity Conditions

Cancer is defined as a group of diseases characterized by abnormal cell growth, expansion, and progression with metastasis. Various signaling pathways are involved in its development. Malignant tumors exhibit a high morbidity and mortality. Cancer research increased our knowledge about some of the underlying mechanisms, but to this day, our understanding of this disease is unclear. High throughput omics technology and bioinformatics were successful in detecting some of the unknown cancer mechanisms. However, novel groundbreaking research and ideas are necessary. A stay in orbit causes biochemical and molecular biological changes in human cancer cells which are first, and above all, due to microgravity (µg). The µg-environment provides conditions that are not reachable on Earth, which allow researchers to focus on signaling pathways controlling cell growth and metastasis. Cancer research in space already demonstrated how cancer cell-exposure to µg influenced several biological processes being involved in cancer. This novel approach has the potential to fight cancer and to develop future cancer strategies. Space research has been shown to impact biological processes in cancer cells like proliferation, apoptosis, cell survival, adhesion, migration, the cytoskeleton, the extracellular matrix, focal adhesion, and growth factors, among others. This concise review focuses on publications related to genetic, transcriptional, epigenetic, proteomic, and metabolomic studies on tumor cells exposed to real space conditions or to simulated µg using simulation devices. We discuss all omics studies investigating different tumor cell types from the brain and hematological system, sarcomas, as well as thyroid, prostate, breast, gynecologic, gastrointestinal, and lung cancers, in order to gain new and innovative ideas for understanding the basic biology of cancer.

Downregulation of miR-138-5p alleviates propofol-induced neurotoxicity and autophagy by regulating SIRT1

BACKGROUND

Propofol, a commonly utilized anesthetic, has been shown to induce neurotoxicity in developing neurons. A previous study showed that microRNA (miR)-138-5p was dysregulated in hippocampus tissue of mice administrated with propofol. The current study aimed to investigate the functions of miR-138-5p and its target gene in propofol-induced neurotoxicity.

METHODS

SH-SY5Y neuronal cells were treated with increasing doses of propofol for indicated time to identify the optimal concentration and treatment time. MiR-138-5p and SIRT1 expression in SH-SY5Y neuronal cells stimulated with propofol were measured by RT-qPCR. Western blotting was performed to quantify protein levels of SIRT1 and autophagy markers. After interference of miR-138-5p and/or SIRT1 expression, the toxicity of SH-SY5Y neuronal cells was evaluated by cell counting kit-8 (CCK-8) assays and flow cytometry. The formation of autophagosomes was estimated by monodansylcadaverine staining.

RESULTS

Propofol induced neurotoxicity in a dose- or time-dependent manner. Propofol upregulated miR-138-5p while downregulating SIRT1 in SH-SY5Y neuronal cells. The propofol-stimulated neurotoxicity and autophagy was inhibited by miR-138-5p knockdown. Moreover, miR-138-5p bound to SIRT1 3'untranslated region. SIRT1 overexpression increased cell viability while inhibiting apoptosis and autophagy in the context of propofol. SIRT1 downregulation reversed the ameliorative effect of miR-138-5p inhibition on propofol-induced neurotoxicity and autophagy.

CONCLUSION

Downregulation of miR-138-5p alleviates propofol-induced neurotoxicity and autophagy via upregulation of SIRT1.

MicroRNA-138: an emerging regulator of skeletal development, homeostasis, and disease

Noncoding microRNAs are powerful epigenetic regulators of cellular processes by their ability to target and suppress expression of numerous protein-coding mRNAs. This multitargeting function is a unique and complex feature of microRNAs. It is now well-described that microRNAs play important roles in regulating the development and homeostasis of many cell/tissue types, including those that make up the skeletal system. In this review, we focus on microRNA-138 (miR-138) and its effects on regulating bone and cartilage cell differentiation and function. In addition to its reported role as a tumor suppressor, miR-138 appears to function as an inhibitor of osteoblast differentiation. This review provides additional information on studies that have attempted to alter miR-138 expression in vivo as a means to dampen ectopic calcification or alter bone mass. However, a review of the published literature on miR-138 in cartilage reveals a number of contradictory and inconclusive findings with respect to regulating chondrogenesis and chondrocyte catabolism. This highlights the need for more research in understanding the role of miR-138 in cartilage biology and disease. Interestingly, a number of studies in other systems have reported miR-138-mediated effects in dampening inflammation and pain responses. Future studies will reveal if a multifunctional role of miR-138 involving suppression of ectopic bone, inflammation, and pain will be beneficial in skeletal conditions such as osteoarthritis and heterotopic ossification.

SIRT1 Asn346 sugar chain promoting collagen deacetylation protective effect on osteoblasts under stress

Silencing type information regulator homolog 1 (SIRT1) is a class of nicotinamide adenine dinucleotide (NAD+) dependent deacetylases, which is the convergence point of important physiological processes in vivo, namely, osteoblast aging, energy metabolism, and bone remodeling. To verify whether the O-acetylglucosamine (O-GlcNAc) modification of SIRT1 in the nucleus of osteoblasts enhances its deacetylase activity under stress and protects osteoblasts through the RANK/RANKL signaling pathway by collagen deacetylation. The R language and online data research identified SIRT1 as being involved in bone metabolism. Enrichment analysis showed that SIRT1 is involved in osteoblast transcription, apoptosis, and deacetylation pathways. Interactive Immuno-blotting and immunofluorescence experiments revealed that SIRT1 and O-glycosylation catalytic enzyme (OGT) were localized in the nucleus. Mass Spectrometry analysis showed that O-glycosylation occurred on the asparagine at the 346th position of SIRT1, and N346th was located in the central domain of SIRT1. Furthermore, the protein structure analysis of PyMol also proved that the OGT binding region was in the central domain of SIRT1. Under physiological conditions, both wtSIRT1 and SIRT1N346R can inhibit RANKL-mediated transcriptional activation. The RT-PCR detection results showed that wtSIRT1 reduced RANKL transcription under the conditions of apoptotic agent treatment. The finding that SIRT1 can regulate the physiological process of bone remodeling through the RANK/RANKL signaling pathway in osteoblasts under stress. The O-glycosylation and deacetylation activity of SIRT1 significantly increased, regulating the balance between osteoblast survival and apoptosis by deacetylation of key proteins such as RANKL.

Exosomes from Microvascular Endothelial Cells under Mechanical Unloading Inhibit Osteogenic Differentiation via miR-92b-3p/ELK4 Axis

Mechanical unloading-related bone loss adversely harms astronauts' health. Nevertheless, the specific molecular basis underlying the phenomenon has not been completely elucidated. Although the bone microvasculature contributes significantly to bone homeostasis, the pathophysiological role of microvascular endothelial cells (MVECs) in bone loss induced by mechanical unloading is not apparent. Here, we discovered that MC3T3-E1 cells could take up exosomes produced by MVECs under clinorotation-unloading conditions (Clino Exos), which then prevented MC3T3-E1 cells from differentiating into mature osteoblasts. Moreover, miR-92b-3p was found to be highly expressed in both unloaded MVECs and derived exosomes. Further experiments demonstrated that miR-92b-3p was transferred into MC3T3-E1 cells by exosomes, resulting in the suppression of osteogenic differentiation, and that encapsulating miR-92b-3p inhibitor into the Clino Exos blocked their inhibitory effects. Furthermore, miR-92b-3p targeted ELK4 and the expression of ELK4 was lessened when cocultured with Clino Exos. The inhibitor-92b-3p-promoted osteoblast differentiation was partially reduced by siRNA-ELK4. Exosomal miR-92b-3p secreted from MVECs under mechanical unloading has been shown for the first time to partially attenuate the function of osteoblasts through downregulation of ELK4, suggesting a potential strategy to protect against the mechanical unloading-induced bone loss and disuse osteoporosis.