Effects of phospholipase D during cultured osteoblast mineralization and bone formation

Lipidomics by Nuclear Magnetic Resonance Spectroscopy and Liquid Chromatography-High-Resolution Mass Spectrometry in Osteosarcoma: A Pilot Study

Cancer is a complex disease that can also affect the younger population; however, it is responsible for a relatively high mortality rate of children and youth, especially in low- and middle-income countries (LMICs). Besides that, lipidomic studies in this age range are scarce. Therefore, we analyzed blood serum samples from young patients (12 to 35 years) with bone sarcoma (osteosarcoma) and compared their lipidomics to the ones from the control group of samples, named healthy control (HC group), using NMR and LC-MS techniques. Furthermore, differences in the lipidomic profiles between OS patients with and without metastasis indicate higher glycerophosphocholine (GPC) and glycerophospholipid (GPL) levels in osteosarcoma and increased cholesterol, choline, polyunsaturated fatty acids (PUFAs), and glycerols during the metastasis. These differences, detected in the peripheral blood, could be used as biomarkers for liquid biopsy.

Expanding the therapeutic potential of Salvia miltiorrhiza: a review of its pharmacological applications in musculoskeletal diseases

Salvia miltiorrhiz, commonly known as "Danshen" in Chinese medicine, has longstanding history of application in cardiovascular and cerebrovascular diseases. Renowned for its diverse therapeutic properties, including promoting blood circulation, removing blood stasis, calming the mind, tonifying the blood, and benefiting the "Qi", recent studies have revealed its significant positive effects on bone metabolism. This potential has garnered attention for its promising role in treating musculoskeletal disorders. Consequently, there is a high anticipation for a comprehensive review of the potential of Salvia miltiorrhiza in the treatment of various musculoskeletal diseases, effectively introducing an established traditional Chinese medicine into a burgeoning field.

AIM OF THE REVIEW

Musculoskeletal diseases (MSDs) present significant challenges to healthcare systems worldwide. Previous studies have demonstrated the high efficacy and prospects of Salvia miltiorrhiza and its active ingredients for treatment of MSDs. This review aims to illuminate the newfound applications of Salvia miltiorrhiza and its active ingredients in the treatment of various MSDs, effectively bridging the gap between an established medicine and an emerging field.

METHODS

In this review, previous studies related to Salvia miltiorrhiza and its active ingredients on the treatment of MSD were collected, the specific active ingredients of Salvia miltiorrhiza were summarized, the effects of Salvia miltiorrhiza and its active ingredients for the treatment of MSDs, as well as their potential molecular mechanisms were reviewed and discussed.

RESULTS

Based on previous publications, Salvianolic acid A, salvianolic acid B, tanshinone IIA are the representative active ingredients of Salvia miltiorrhiza. Their application has shown significant beneficial outcomes in osteoporosis, fractures, and arthritis. Salvia miltiorrhiza and its active ingredients protect against MSDs by regulating different signaling pathways, including ROS, Wnt, MAPK, and NF-κB signaling.

CONCLUSION

Salvia miltiorrhiza and its active ingredients demonstrate promising potential for bone diseases and have been explored across a wide variety of MSDs. Further exploration of Salvia miltiorrhiza's pharmacological applications in MSDs holds great promise for advancing therapeutic interventions and improving the lives of patients suffering from these diseases.

Osteosarcoma cells/cell lines are not appropriate for studies on bone regeneration in vitro

Cite this article: Bone Joint Res 2023;12(5):311–312.

Functional Role of Phospholipase D in Bone Metabolism

Phospholipase D (PLD) proteins are major enzymes that regulate various cellular functions, such as cell growth, cell migration, membrane trafficking, and cytoskeletal dynamics. As they are responsible for such important biological functions, PLD proteins have been considered promising therapeutic targets for various diseases, including cancer and vascular and neurological diseases. Intriguingly, emerging evidence indicates that PLD1 and PLD2, 2 major mammalian PLD isoenzymes, are the key regulators of bone remodeling; this suggests that these isozymes could be used as potential therapeutic targets for bone diseases, such as osteoporosis and rheumatoid arthritis. PLD1 or PLD2 deficiency in mice can lead to decreased bone mass and dysregulated bone homeostasis. Although both mutant mice exhibit similar skeletal phenotypes, PLD1 and PLD2 play distinct and nonredundant roles in bone cell function. This review summarizes the physiological roles of PLD1 and PLD2 in bone metabolism, focusing on recent findings of the biological functions and action mechanisms of PLD1 and PLD2 in bone cells.

Phospholipase D and cancer metastasis: A focus on exosomes

In mammals, phospholipase D (PLD) enzymes involve 6 isoforms, of which only three have established lipase activity to produce the signaling lipid phosphatidic acid (PA). This phospholipase activity has been postulated to contribute to cancer progression for over three decades now, but the exact mechanisms involved have yet to be uncovered. Indeed, using various models, an altered PLD activity has been proposed altogether to increase cell survival rate, promote angiogenesis, boost rapamycin resistance, and favor metastasis. Although for some part, the molecular pathways by which this increase in PA is pro-oncogenic are partially known, the pleiotropic functions of PA make it quite difficult to distinguish which among these simple signaling pathways is responsible for each of these PLD facets. In this review, we will describe an additional potential contribution of PA generated by PLD1 and PLD2 in the biogenesis, secretion, and uptake of exosomes. Those extracellular vesicles are now viewed as membrane vehicles that carry informative molecules able to modify the fate of receiving cells at distance from the original tumor to favor homing of metastasis. The perspectives for a better understanding of these complex role of PLDs will be discussed.

Dickkopf1 (Dkk1) Alleviates Vascular Calcification by Regulating the Degradation of Phospholipase D1 (PLD1)

Vascular calcification (VC) is a significant risk factor for cardiovascular mortality and morbidity in patients with atherosclerosis (AS), chronic kidney disease, and diabetes. Dickkopf1 (Dkk1) is a multifunctional secreted glycoprotein that has been explored as a novel potential antitumor target. Recently, Dkk1 was shown to be closely associated with AS development. However, the role of Dkk1 in VC remains elusive. In this study, we explored the role and molecular mechanisms of Dkk1 in VC based on a smooth muscle-specific Dkk1-knockout (Dkk1SMKO) mouse model. Our data indicated that Dkk1 expression was decreased under calcifying conditions and that Dkk1 overexpression alleviated high phosphate-induced vascular calcification. In vivo, smooth muscle Dkk1-specific knockout aggravated vascular calcification in mice. However, phospholipase D1 (PLD1) overexpression partially weakened the protective effect of Dkk1 against vascular calcification. Mechanistically, Dkk1 slowed vascular calcification by promoting the degradation of PLD1 via the regulating autophagosome formation and maturation. In conclusion, we found that Dkk1 could alleviate vascular calcification by regulating the degradation of PLD1.

Phospholipase D2 controls bone homeostasis by modulating M-CSF-dependent osteoclastic cell migration and microtubule stability

Phospholipase D2 (PLD2), a signaling protein, plays a central role in cellular communication and various biological processes. Here, we show that PLD2 contributes to bone homeostasis by regulating bone resorption through osteoclastic cell migration and microtubule-dependent cytoskeletal organization. Pld2-deficient mice exhibited a low bone mass attributed to increased osteoclast function without altered osteoblast activity. While Pld2 deficiency did not affect osteoclast differentiation, its absence promoted the migration of osteoclast lineage cells through a mechanism involving M-CSF-induced activation of the PI3K–Akt–GSK3β signaling pathway. The absence of Pld2 also boosted osteoclast spreading and actin ring formation, resulting in elevated bone resorption. Furthermore, Pld2 deletion increased microtubule acetylation and stability, which were later restored by treatment with a specific inhibitor of Akt, an essential molecule for microtubule stabilization and osteoclast bone resorption activity. Interestingly, PLD2 interacted with the M-CSF receptor (c-Fms) and PI3K, and the association between PLD2 and c-Fms was reduced in response to M-CSF. Altogether, our findings indicate that PLD2 regulates bone homeostasis by modulating osteoclastic cell migration and microtubule stability via the M-CSF-dependent PI3K–Akt–GSK3β axis.

A signaling protein that regulates bone resorption may prove a useful target in treating skeletal conditions such as osteoporosis and rheumatoid arthritis. Bone is synthesized by cells called osteoblasts, while osteoclasts trigger bone resorption, keeping the skeleton healthy. Imbalances in this recycling process are common in bone disorders. Je-Young Choi and Hyun-Ju Kim at Kyungpook National University in Daegu, South Korea, and co-workers demonstrated that phospholipase D2 (PLD2), a membrane protein, directly regulates bone resorption in mice. Mice without the Pld2 gene had increased osteoclast activity, resulting in low bone mass. The absence of PLD2 promotes the migration of osteoclasts via a particular signaling pathway. This increased the organization of microtubules, polymers that help form the cytoskeleton. The results suggest that regulating PLD2 activity could form the basis of a future treatment method.

Intracellular density is a novel indicator of differentiation stages of murine osteoblast lineage cells

Osteoblasts are primary bone-making cells originating from mesenchymal stem cells (MSCs) in the bone marrow. The differentiation of MSCs to mature osteoblasts involves an intermediate stage called preosteoblasts, but the details of this process remain unclear. This study focused on the intracellular density of immature osteoblast lineage cells and hypothesized that the density might vary during differentiation and might be associated with the differentiation stages of osteoblast lineage cells. This study aimed to clarify the relationship between intracellular density and differentiation stages using density gradient centrifugation. Primary murine bone marrow stromal cell cultures were prepared in an osteogenic induction medium, and cells were separated into three fractions (low, intermediate, and high-density). The high-density fraction showed elevated expression of osteoblast differentiation markers (Sp7, Col1a1, Spp1, and Bglap) and low expression of MSC surface markers (Sca-1, CD73, CD105, and CD106). In contrast, the low-density fraction showed a high expression of MSC surface markers. These results indicated that intracellular density increased during differentiation from preosteoblasts to committed osteoblasts. Intracellular density may be a novel indicator for osteoblast differentiation stages. Density gradient centrifugation is a novel technique to study the process by which preosteoblasts transform into bone-forming cells.

miRNA Let-7a-5p targets RNA KCNQ1OT1 and Participates in Osteoblast Differentiation to Improve the Development of Osteoporosis

It is known that miRNA mediates the formation of osteogenesis, but the mechanism by which miRNA let-7a-5p regulates osteogenesis in osteoporosis (OP) is not yet understood. This paper aims to probe into the regulatory mechanism of miRNA let-7a-5p in the development of OP. Fresh femoral trabecular bones of patients with osteoporotic fracture (OP group, n = 25) and non-OP osteoarthritis (Non-OP group, n = 23) who underwent hip replacement in our hospital from December 2016 to December 2019 were collected. The expression and protein levels of miRNA let-7a-5p and V-AKT murine thymoma viral oncogene homolog 3 (RNA KCNQ1OT1) were detected. C2C12 cells were purchased and osteogenic differentiation model was constructed by BMP2 induction. After miRNA let-7a-5p up-regulation or down-regulation by transfection of corresponding mimics and inhibitors, the impacts of miRNA let-7a-5p and RNA KCNQ1OT1 on osteogenic differentiation-related factors (OC, ALP, COL1A1) in C2C12 cells were analyzed. The determination of targeting correlation of miRNA let-7a-5p with RNA KCNQ1OT1 was performed by dual-luciferase reporter (DLR). In OP samples, miRNA let-7a-5p was notably declined while RNA KCNQ1OT1 were remarkably up-regulated. MiRNA let-7a-5p reduced in C2C12 cells as BMP2 treatment proceeded. MiRNA let-7a-5p up-regulation or RNA KCNQ1OT1 down-regulation increased OC, ALP, COL1A1 levels and ALP activity. RNA KCNQ1OT1 was directly targeted to miR-497-5p. RNA KCNQ1OT1 up-regulation weakened the promoting effect of miRNA let-7a-5p up-regulation on osteoblast differentiation. MiRNA let-7a-5p up-regulation can target to reduce RNA KCNQ1OT1 and promote osteoblast differentiation, thereby improving the development of osteoporosis.

Cyanidin-3-glucoside Regulates Osteoblast Differentiation via the ERK1/2 Signaling Pathway

Osteoporosis, characterized by a gradual decrease in the number of osteoblasts and a gradual increase in bone resorption of osteoclasts in bone tissue, is a global chronic disease, which severely impairs the quality of life of the elderly. Therefore, it is extremely urgent to study the prevention and treatment of osteoporosis. It has been reported that anthocyanins can regulate bone metabolism and prevent osteoporosis. Cyanidin-3-O-glucoside (C3G), the most common type of anthocyanin in nature, widely exists in a variety of vegetables and fruits. Although it has been shown that C3G has multiple effects on osteoclasts, its impact(s) and underlying mechanism(s) on osteoblasts are still not clear. Here, we evaluated the effect of C3G on cell proliferation and differentiation of osteoblasts (extracted from the hip joint of patients with osteoporosis) and MC3T3-E1 (a kind of osteoblast cell line from mice). We also test the ability of osteoblasts to mineralize after C3G treatment. To find the underlying mechanism of the above effects, we further evaluated the role of the ERK signaling pathway in C3G regulation of osteoblasts. The results showed that C3G treatment enhanced osteoblast proliferation rate, osteoblast mineralization points, the mRNA levels and protein expression levels of OC (osteocalcin), and the level of ERK phosphorylation, which could be blocked by pretreatment with ERK signaling pathway inhibitor. The above results not only indicate that the ERK pathway was involved in C3G regulation of osteoblast differentiation but also provide strong suggestive evidence that osteoblasts may be promising targets in preventive and therapeutic strategies for osteoporosis.

From organic and inorganic phosphates to valvular and vascular calcifications

Calcification of the arterial wall and valves is an important part of the pathophysiological process of peripheral and coronary atherosclerosis, aortic stenosis, ageing, diabetes, and chronic kidney disease. This review aims to better understand how extracellular phosphates and their ability to be retained as calcium phosphates on the extracellular matrix initiate the mineralization process of arteries and valves. In this context, the physiological process of bone mineralization remains a human model for pathological soft tissue mineralization. Soluble (ionized) calcium precipitation occurs on extracellular phosphates; either with inorganic or on exposed organic phosphates. Organic phosphates are classified as either structural (phospholipids, nucleic acids) or energetic (corresponding to phosphoryl transfer activities). Extracellular phosphates promote a phenotypic shift in vascular smooth muscle and valvular interstitial cells towards an osteoblast gene expression pattern, which provokes the active phase of mineralization. A line of defense systems protects arterial and valvular tissue calcifications. Given the major roles of phosphate in soft tissue calcification, phosphate mimetics, and/or prevention of phosphate dissipation represent novel potential therapeutic approaches for arterial and valvular calcification.

Deletion of phospholipase D1 decreases bone mass and increases fat mass via modulation of Runx2, β-catenin-osteoprotegerin, PPAR-γ and C/EBPα signaling axis

In osteoporosis, mesenchymal stem cells (MSCs) prefer to differentiate into adipocytes at the expense of osteoblasts. Although the balance between adipogenesis and osteogenesis has been closely examined, the mechanism of commitment determination switch is unknown. Here we demonstrate that phospholipase D1 (PLD1) plays a key switch in determining the balance between bone and fat mass. Ablation of Pld1 reduced bone mass but increased fat in mice. Mechanistically, Pld1^/- MSCs inhibited osteoblast differentiaion with diminished Runx2 expression, while osteoclast differentiation was accelerated in Pld1^-/- bone marrow-derived macrophages. Pld1^-/- osteoblasts showed decreased expression of osteogenic makers. Increased number and resorption activity of osteoclasts in Pld1^-/- mice were corroborated with upregulation of osteoclastogenic markers. Moreover, Pld1^-/- osteoblasts reduced β-catenin mediated-osteoprotegerin (OPG) with increased RANKL/OPG ratio which resulted in accelerated osteoclast differentiation. Thus, low bone mass with upregulated osteoclasts could be due to the contribution of both osteoblasts and osteoclasts during bone remodeling. Moreover, ablation of Pld1 further increased bone loss in ovariectomized mice, suggesting that PLD1 is a negative regulator of osteoclastogenesis. Furthermore, loss of PLD1 increased adipogenesis, body fat mass, and hepatic steatosis along with upregulation of PPAR-γ and C/EBPα. Interestingly, adipocyte-specific Pld1 transgenic mice rescued the compromised phenotypes of fat mass and adipogenesis in Pld1 knockout mice. Collectively, PLD1 regulated the bifurcating pathways of mesenchymal cell lineage into increased osteogenesis and decreased adipogenesis, which uncovered a previously unrecognized role of PLD1 in homeostasis between bone and fat mass.

Prostate cancer-derived exosomes promote osteoblast differentiation and activity through phospholipase D2

Prostate cancer (PCa) is the most frequent cancer in men aged 65 and over. PCa mainly metastasizes in the bone, forming osteosclerotic lesions, inducing pain, fractures, and nerve compression. Cancer cell-derived exosomes participate in the metastatic spread, ranging from oncogenic reprogramming to the formation of pre-metastatic niches. Moreover, exosomes were recently involved in the dialog between PCa cells and the bone metastasis microenvironment. Phospholipase D (PLD) isoforms PLD1/2 catalyze the hydrolysis of phosphatidylcholine to yield phosphatidic acid (PA), regulating tumor progression and metastasis. PLD is suspected to play a role in exosomes biogenesis. We aimed to determine whether PCa-derived exosomes, through PLD, interact with the bone microenvironment, especially osteoblasts, during the metastatic process. Here we demonstrate for the first time that PLD2 is present in exosomes of C4-2B and PC-3 cells. C4-2B-derived exosomes activate proliferation and differentiation of osteoblasts models, by stimulating ERK 1/2 phosphorylation, by increasing the tissue-nonspecific alkaline phosphatase activity and the expression of osteogenic differentiation markers. Contrariwise, when C4-2B exosomes are generated in the presence of halopemide, a PLD pan-inhibitor, they lose their ability to stimulate osteoblasts. Furthermore, the number of released exosomes diminishes significantly (-40%). When the PLD product PA is combined with halopemide, exosome secretion is fully restored. Taken together, our results indicate that PLD2 stimulates exosome secretion in PCa cell models as well as their ability to increase osteoblast activity. Thus, PLD2 could be considered as a potent player in the establishment of PCa bone metastasis acting through tumor cell derived-exosomes.

Increased phospholipase D activity contributes to tumorigenesis in prostate cancer cell models

Prostate cancer (PCa) is the most frequent cancer among men and the first cause of death over 65. Approximately 90% of patients with advanced disease will develop bone metastasis, which dramatically reduces long-term survival. Therefore, effective therapies need to be developed, especially when disease is still well-localized. Phospholipase D (PLD), an enzyme that hydrolyzes phosphatidylcholine to yield phosphatidic acid, regulates several cellular functions as proliferation, survival, migration or vesicular trafficking. PLD is implicated in numerous diseases such as neurodegenerative, cardiovascular, autoimmune disorders or cancer. Indeed, PLD controls different aspects of oncogenesis including tumor progression and resistance to targeted therapies such as radiotherapy. PLD1 and PLD2 are the only isoforms with catalytic activity involved in cancer. Surprisingly, studies deciphering the role of PLD in the pathophysiology of PCa are scarce. Here we describe the correlation between PLD activity and PLD1 and PLD2 expression in PCa bone metastasis-derived cell lines C4-2B and PC-3. Next, by using PLD pharmacological inhibitors and RNA interference strategy, we validate the implication of PLD1 and PLD2 in cell viability, clonogenicity and proliferation of C4-2B and PC-3 cells and in migration capacity of PC-3 cells. Last, we show an increase in PLD activity as well as PLD2 protein expression during controlled starvation of PC-3 cells, concomitant with an augmentation of its migration capacity. Specifically, upregulation of PLD activity appears to be PKC-independent. Taken together, our results indicate that PLD, and in particular PLD2, could be considered as a potential therapeutic target for the treatment of PCa-derived bone metastasis.