OSU53 Rescues Human OB-6 Osteoblastic Cells from Dexamethasone through Activating AMPK Signaling

Small-molecule amines: a big role in the regulation of bone homeostasis

Numerous small-molecule amines (SMAs) play critical roles in maintaining bone homeostasis and promoting bone regeneration regardless of whether they are applied as drugs or biomaterials. On the one hand, SMAs promote bone formation or inhibit bone resorption through the regulation of key molecular signaling pathways in osteoblasts/osteoclasts; on the other hand, owing to their alkaline properties as well as their antioxidant and anti-inflammatory features, most SMAs create a favorable microenvironment for bone homeostasis. However, due to a lack of information on their structure/bioactivity and underlying mechanisms of action, certain SMAs cannot be developed into drugs or biomaterials for bone disease treatment. In this review, we thoroughly summarize the current understanding of SMA effects on bone homeostasis, including descriptions of their classifications, biochemical features, recent research advances in bone biology and related regulatory mechanisms in bone regeneration. In addition, we discuss the challenges and prospects of SMA translational research.

Elevated lncRNA MIAT in peripheral blood mononuclear cells contributes to post-menopausal osteoporosis

Inflammatory cytokines contribute to the development of osteoporosis with sophisticated mechanisms. Globally alteration of long-chain non-coding RNA was screened in osteoporosis, while we still know little about their functional role in the inflammatory cytokine secretion. In this study, we collected the peripheral blood mononuclear cells (PBMCs) from post-menopausal osteoporosis patients to measure lncRNA MIAT (lncMIAT) expression levels, and explored the molecular mechanism of lncMIAT induced inflammatory cytokine secretion. We identified increased lncMIAT expression in the PBMCs of post-menopausal osteoporosis patients, which was an important predictive biomarker for the diagnosis. LncMIAT expression in PBMCs was positively correlated with the inflammatory cytokine secretion. Mechanism study indicated that lncMIAT increased the expression levels of p38MAPK by crosstalk with miR-216a in PBMCs. The lncMIAT/miR-216a/p38MAPK signaling contributed predominantly to the increased inflammatory cytokine secretion in the PBMCs from postmenopausal osteoporosis. In conclusion, we identified that increased lncMIAT in PBMCs induced inflammatory cytokine secretion, which contributed to the development of post-menopausal osteoporosis. lncMIAT/miR-216a axis was critical for the regulation of AMPK/p38MAPK signaling, which may be a promising therapeutic target for osteoporosis treatment by inflammatory cytokine inhibition.

Aucubin prevents steroid-induced osteoblast apoptosis by enhancing autophagy via AMPK activation

Steroid‐induced osteoblast apoptosis is a crucial pathological process in steroid‐induced osteonecrosis of the femoral head (SONFH). Autophagy can resist apoptosis and AMPK plays an important role in autophagy regulation. Aucubin from the small tree Eucommia ulmoides Oliv., which has a long history of use in orthopaedics and traumatology in Asian medicine, can promote bone formation, but whether it can slow or prevent steroid‐osteoblast apoptosis is unclear. Therefore, we investigated the pathogenesis of SONFH and how the osteoblast responds to aucubin under the dexamethasone stimulation. In human femoral head osteonecrosis specimens, we found that the autophage and apoptosis level were increased, and the AMPK signalling was crucial to autophagy. We observed that aucubin could prevent dexamethasone‐induced apoptosis in osteoblasts by enhancing the level of autophagy. Further, we confirmed that the regulatory effect of aucubin on autophagy and apoptosis was achieved by activating AMPK signalling. We have demonstrated a mechanism of disease progression and shown that aucubin could enhance autophagy through AMPK signalling to prevent osteoblast apoptosis. These findings provide a basis for the further investigation of the potential therapeutic role of aucubin in the SONFH.

AMP-activated protein kinase and the down-stream activated process of autophagy regulate the osteogenic differentiation of human dental follicle cells

OBJECTIVE

Dental follicle cells (DFCs) are progenitors of alveolar osteoblasts. AMP-activated protein kinase (AMPK) and the down-stream activated autophagy process play a key role in cellular energy and metabolic homeostasis and are involved in many biological processes including differentiation. Previous studies showed ambiguous results about the role of AMPK and autophagy in osteogenic differentiation of various osteogenic progenitors, but the role of AMPK and autophagy in DFCs is unknown. This study examined the role of AMPK and autophagy in the osteogenic differentiation of DFCs.

MATERIALS AND METHODS

We evaluated the expression of AMPK isoforms and autophagy markers during osteogenic differentiation via Western Blot analyses and the impact of AMPK / autophagy activators and inhibitors and siRNAs on osteogenic differentiation via ALP activity assay, Alizarin Red staining and Real-Time Reverse-Transcription PCR.

RESULTS

We have shown that expression of AMPK and autophagy markers are regulated during osteogenic differentiation and that activation of AMPK inhibits the ALP activity and other osteogenic markers after induction of osteogenic differentiation, while inhibition of AMPK and autophagy increased the expression of some osteogenic markers. In long-term cultures with osteogenic differentiation medium, however, both the activation and the inhibition of AMPK significantly inhibited biomineralization of DFCs. In contrast, activation or inhibition of autophagy barely affected early differentiation markers, while autophagy inhibition enhanced biomineralization and autophagy activation diminished mineralization capability of DFCs.

CONCLUSIONS

AMPK regulates the osteogenic differentiation in earlier stages while indirectly affecting biomineralization at least partly via autophagy. The osteogenic differentiation of DFCs is sensitive to changes in AMPK and autophagic activity.

MicroRNA-155 inhibition up-regulates LEPR to inhibit osteoclast activation and bone resorption via activation of AMPK in alendronate-treated osteoporotic mice

Osteoporosis is characterized by a progressive increase in bone fragility, leading to low bone mass and structural deterioration of bone tissue. MicroRNA-155 (miR-155) is highly expressed in osteoporosis. Thus, the current study aimed to investigate the effect of miR-155 on the inhibition of osteoclast activation and bone resorption by targeting leptin receptor (LEPR) through the adenosine monophosphate activated protein kinase (AMPK) pathway in alendronate-treated osteoporotic mice. An osteoporosis mouse model was established to examine the bone tension and bone density and the expression of miR-155 in osteoclasts. Binding sites between miR-155 and LEPR were verified. Osteoclasts in the treatment group were transfected with different mimic, inhibitor, vector, or siRNA for subsequent experiments. The expression of miR-155, LEPR, AMPK, p-AMPK, RANKL, OPG, M-CSF, RANK, TRAP, Bax, Bcl-2, and the contents of TNF-α and IL-1β were all examined. The proliferation and bone resorption of osteoclasts were also detected. Mice with osteoporosis exhibited decreased bone density and bone tension, along with elevated expression of miR-155. LEPR was verified as a target gene of miR-155. Down-regulated miR-155 was found to increase the expression of LEPR, AMPK, p-AMPK, OPG, Bax, decrease expression of TNF-α, IL-1β, RANKL, M-CSF, RANK, TRAP, Bcl-2, inhibit the cell proliferation and bone resorption of osteoclasts. Taken together, decreased miR-155 up-regulated LEPR via activation of AMPK, which ultimately repressed osteoclast activation and bone resorption of osteoclasts in alendronate-treated osteoporotic mice.

Activation of AMPK by OSU53 protects spinal cord neurons from oxidative stress

The present study tested the potential effect of OSU53, a novel AMPK activator, against hydrogen peroxide (H2O2)-induced spinal cord neuron damages. Treatment with OSU53 attenuated H2O2-induced death and apoptosis of primary murine spinal cord neurons. OSU53 activated AMPK signaling, which is required for its actions in spinal cord neurons. The AMPK inhibitor Compound C or AMPKα1 siRNA almost abolished OSU53-mediated neuroprotection against H2O2. On the other hand, sustained-activation of AMPK by introducing the constitutive-active AMPKα1 mimicked OSU53's actions, and protected spinal cord neurons from oxidative stress. OSU53 significantly attenuated H2O2-induced reactive oxygen species production, lipid peroxidation and DNA damages in spinal cord neurons. Additionally, OSU53 increased NADPH content and heme oxygenase-1 mRNA expression in H2O2-treated spinal cord neurons. Together, we indicate that targeted-activation of AMPK by OSU53 protects spinal cord neurons from oxidative stress.

Oxidative stress and chronic inflammation in osteoarthritis: can NRF2 counteract these partners in crime?

Osteoarthritis (OA) is an age-related joint degenerative disease associated with pain, joint deformity, and disability. The disease starts with cartilage damage but then progressively involves subchondral bone, causing an imbalance between osteoclast-driven bone resorption and osteoblast-driven remodeling. Here, we summarize the data for the role of oxidative stress and inflammation in OA pathology and discuss how these two processes are integrated during OA progression, as well as their contribution to abnormalities in cartilage/bone metabolism and integrity. At the cellular level, oxidative stress and inflammation are counteracted by transcription factor nuclear factor erythroid p45-related factor 2 (NRF2), and we describe the regulation of NRF2, highlighting its role in OA pathology. We also discuss the beneficial effect of some phytonutrients, including the therapeutic potential of NRF2 activation, in OA.