Effects of the proteasome inhibitor, bortezomib, on cytodifferentiation and mineralization of periodontal ligament cells

Lysosomal acid lipase regulates bioenergetic process during the cytodifferentiation of human periodontal ligament cells

Lipid metabolism is one of energy metabolic pathways that produce adenosine triphosphate (ATP). In this pathway, lysosomal acid lipase (LAL) encoded by Lipase A (LIPA), plays an important role in catalyzing lipids to fatty acids (FAs), which drive oxidative phosphorylation (OXPHOS) and generate ATP. Previously, we found that a LIPA single nucleotide polymorphism rs143793106, which decreases the LAL activity, suppressed the cytodifferentiation of human periodontal ligament (HPDL) cells. However, the mechanisms underlying that suppression are still not fully clarified. Thus, we aimed to investigate the mechanisms regulating the cytodifferentiation of HPDL cells by LAL in terms of energy metabolism. We performed the osteogenic induction of HPDL cells with or without Lalistat-2, a LAL inhibitor. To visualize lipid droplet (LD) utilization, we performed confocal microscopy on HPDL cells. We also performed real-time PCR to analyze the gene expression of calcification-related and metabolism-related genes. Furthermore, we measured the ATP production rate from two major energy production pathways, OXPHOS and glycolysis, and OXPHOS-related parameters of HPDL cells during their cytodifferentiation. We found that LDs were utilized during the cytodifferentiation of HPDL cells. Alkaline phosphatase (ALPL), collagen type 1 alpha 1 chain (COL1A1), ATP synthase F1 subunit alpha (ATP5F1A), and carnitine palmitoyltransferase 1A (CPT1A) mRNA expressions were upregulated, whereas lactate dehydrogenase A (LDHA) mRNA expression was downregulated. Additionally, total ATP production rate was significantly increased. In contrast, in the presence of Lalistat-2, LD utilization was inhibited and ALPL, COL1A1, and ATP5F1A mRNA expression was downregulated. Additionally, ATP production rate and spare respiratory capacity of the OXPHOS pathway were decreased in HPDL cells during their cytodifferentiation. Collectively, the defect of LAL in HPDL cells decreased LD utilization and OXPHOS capacity, resulting in reduced energy to sustain the adequate ATP production required for the cytodifferentiation of HPDL cells. Thus, LAL is important for periodontal tissue homeostasis as a regulator of bioenergetic process of HPDL cells.

Lipase-a single-nucleotide polymorphism rs143793106 is associated with increased risk of aggressive periodontitis by negative influence on the cytodifferentiation of human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Aggressive periodontitis (AgP) is characterized by general health and rapid destruction of periodontal tissue. The familial aggregation of this disease highlights the involvement of genetic factors in its pathogeny. We conducted a genome-wide association study (GWAS) to identify AgP-related genes in a Japanese population, and the lipid metabolism-related gene, lipase-a, lysosomal acid type (LIPA), was suggested as an AgP candidate gene. However, there is no report about the expression and function(s) of LIPA in periodontal tissue. Hence, we studied the involvement of how LIPA and its single-nucleotide polymorphism (SNP) rs143793106 in AgP by functional analyses of LIPA and its SNP in human periodontal ligament (HPDL) cells.

MATERIALS AND METHODS

GWAS was performed using the genome database of Japanese AgP patients, and the GWAS result was confirmed using Sanger sequencing. We examined the mRNA expression level of LIPA and the protein expression level of the encoded protein lysosomal acid lipase (LAL) in periodontium-composing cells using conventional and real-time polymerase chain reaction (PCR) and western blotting, respectively. Lentiviral vectors expressing LIPA wild-type (LIPA WT) and LIPA SNP rs143793106 (LIPA mut) were transfected into HPDL cells. Western blotting was performed to confirm the transfection. LAL activity of transfected HPDL cells was determined using the lysosomal acid lipase activity assay. Transfected HPDL cells were cultured in mineralization medium. During the cytodifferentiation of transfected HPDL cells, mRNA expression of calcification-related genes, alkaline phosphatase (ALPase) activity and calcified nodule formation were assessed using real-time PCR, ALPase assay, and alizarin red staining, respectively.

RESULTS

The GWAS study identified 11 AgP-related candidate genes, including LIPA SNP rs143793106. The minor allele frequency of LIPA SNP rs143793106 in AgP patients was higher than that in healthy subjects. LIPA mRNA and LAL protein were expressed in HPDL cells; furthermore, they upregulated the cytodifferentiation of HPDL cells. LAL activity was lower in LIPA SNP-transfected HPDL cells during cytodifferentiation than that in LIPA WT-transfected HPDL cells. In addition, ALPase activity, calcified nodule formation, and calcification-related gene expression levels were lower during cytodifferentiation in LIPA SNP-transfected HPDL cells than those in LIPA WT-transfected HPDL cells.

CONCLUSION

LIPA, identified as an AgP-related gene in a Japanese population, is expressed in HPDL cells and is involved in regulating cytodifferentiation of HPDL cells. LIPA SNP rs143793106 suppressed cytodifferentiation of HPDL cells by decreasing LAL activity, thereby contributing to the development of AgP.

Advanced Biomaterials and Techniques for Oral Tissue Engineering and Regeneration-A Review

The reconstruction or repair of oral and maxillofacial functionalities and aesthetics is a priority for patients affected by tooth loss, congenital defects, trauma deformities, or various dental diseases. Therefore, in dental medicine, tissue reconstruction represents a major interest in oral and maxillofacial surgery, periodontics, orthodontics, endodontics, and even daily clinical practice. The current clinical approaches involve a vast array of techniques ranging from the traditional use of tissue grafts to the most innovative regenerative procedures, such as tissue engineering. In recent decades, a wide range of both artificial and natural biomaterials and scaffolds, genes, stem cells isolated from the mouth area (dental follicle, deciduous teeth, periodontal ligament, dental pulp, salivary glands, and adipose tissue), and various growth factors have been tested in tissue engineering approaches in dentistry, with many being proven successful. However, to fully eliminate the problems of traditional bone and tissue reconstruction in dentistry, continuous research is needed. Based on a recent literature review, this paper creates a picture of current innovative strategies applying dental stem cells for tissue regeneration in different dental fields and maxillofacial surgery, and offers detailed information regarding the available scientific data and practical applications.

GLP-1 Receptor Activation Abrogates β-Cell Dysfunction by PKA Cα-Mediated Degradation of Thioredoxin Interacting Protein

Glucagon-like peptide 1 receptor (GLP-1R) agonist (Exendin-4) is a well-known agent used to improve β-cell dysfunctions via protein kinase A (PKA), but the detailed downstream molecular mechanisms are still elusive. We have now found that PKA Cα mediated- TXNIP phosphorylation and degradation played a vital role in the β-cell protective role of exendin-4. After PKA activator (Exendin-4 or FSK) treatment, PKA Cα could directly interact with TXNIP by bimolecular fluorescence complementation and Co-IP assays in INS-1 cells. And PKA Cα overexpression decreased TXNIP level, whereas TXNIP level was largely increased in PKA Cα-KO β-cells by CRISPR-Cas9. Interestingly, TXNIP overexpression or PKA Cα-KO has impaired β-cell functions, including loss of insulin secretion and activation of inflammation. PKA Cα directly phosphorylated TXNIP at Ser307 and Ser308 positions, leading to its degradation via activation of cellular proteasome pathway. Consistent with this observation, TXNIP (S307/308A) mutant resisted the degradation effects of PKA Cα. However, exendin-4 neither affected TXNIP level in TXNIP (S307/308A) mutant overexpressed β-cells nor in PKA Cα-KO β-cells. Moreover, exendin-4 treatment reduced the inflammation gene expression in TXNIP overexpressed β-cells, but exendin-4 treatment has no effect on the inflammation gene expression in TXNIP (S307/308A) overexpressed β-cells. In conclusion, our study reveals the integral role of PKA Cα/TXNIP signaling in pancreatic β-cells and suggests that PKA Cα-mediated TXNIP degradation is vital in β-cell protective effects of exendin-4.

Bortezomib Facilitates Reparative Dentin Formation after Pulp Access Cavity Preparation in Mouse Molar

INTRODUCTION

The aim of this study was to evaluate in vitro and ex vivo roles of bortezomib, a proteasome inhibitor that binds to the active site of the 26S proteasome, in tertiary dentin formation.

METHODS

We established pulpal access cavity preparation that was treated with or without bortezomib before direct pulp capping with a calcium hydroxide-based material. We also analyzed bone morphogenetic protein (Bmp)- and Wnt-related signaling molecules using quantitative real-time polymerase chain reaction.

RESULTS

In the short-term observation period, the bortezomib-treated pulp specimens showed the period-altered immunolocalization patterns of nestin, CD31, and myeloperoxidase, whereas the control specimens did not. The bortezomib-treated group showed a complete dentin bridge with very few irregular tubules after 42 days. The micro-computed tomographic images showed more apparent dentin bridge structures in the treated specimens than were in the controls. Quantitative real-time polymerase chain reaction analysis showed up-regulated Bmp and Wnt.

CONCLUSIONS

These findings revealed that treatment with 1 μmol/L bortezomib induced reparative dentin formation that facilitated the maintenance of the integrity of the remaining pulpal tissue via early vascularization and regulation of Bmp and Wnt signaling.

Ubiquitination in Periodontal Disease: A Review

Periodontal disease (periodontitis) is a chronic inflammatory condition initiated by microbial infection that leads to gingival tissue destruction and alveolar bone resorption. The periodontal tissue's response to dental plaque is characterized by the accumulation of polymorphonuclear leukocytes, macrophages, and lymphocytes, all of which release inflammatory mediators and cytokines to orchestrate the immunopathogenesis of periodontal disease. Ubiquitination is achieved by a mechanism that involves a number of factors, including an ubiquitin-activating enzyme, ubiquitin-conjugating enzyme, and ubiquitin-protein ligase. Ubiquitination is a post-translational modification restricted to eukaryotes that are involved in essential host processes. The ubiquitin system has been implicated in the immune response, development, and programmed cell death. Increasing numbers of recent reports have provided evidence that many approaches are delivering promising reports for discovering the relationship between ubiquitination and periodontal disease. The scope of this review was to investigate recent progress in the discovery of ubiquitinated protein in diseased periodontium and to discuss the ubiquitination process in periodontal diseases.

Sphingomyelin Phosphodiesterase 3 Enhances Cytodifferentiation of Periodontal Ligament Cells

Sphingomyelin phosphodiesterase 3 ( Smpd3), which encodes neutral sphingomyelinase 2 (nSMase2), is a key molecule for skeletal development as well as for the cytodifferentiation of odontoblasts and alveolar bone. However, the effects of nSMase2 on the cytodifferentiation of periodontal ligament (PDL) cells are still unclear. In this study, the authors analyzed the effects of Smpd3 on the cytodifferentiation of human PDL (HPDL) cells. The authors found that Smpd3 increases the mRNA expression of calcification-related genes, such as alkaline phosphatase (ALPase), type I collagen, osteopontin, Osterix (Osx), and runt-related transcription factor (Runx)-2 in HPDL cells. In contrast, GW4869, an inhibitor of nSMase2, clearly decreased the mRNA expression of ALPase, type I collagen, and osteocalcin in HPDL cells, suggesting that Smpd3 enhances HPDL cytodifferentiation. Next, the authors used exome sequencing to evaluate the genetic variants of Smpd3 in a Japanese population with aggressive periodontitis (AgP). Among 44 unrelated subjects, the authors identified a single nucleotide polymorphism (SNP), rs145616324, in Smpd3 as a putative genetic variant for AgP among Japanese people. Moreover, Smpd3 harboring this SNP did not increase the sphingomyelinase activity or mRNA expression of ALPase, type I collagen, osteopontin, Osx, or Runx2, suggesting that this SNP inhibits Smpd3 such that it has no effect on the cytodifferentiation of HPDL cells. These data suggest that Smpd3 plays a crucial role in maintaining the homeostasis of PDL tissue.

A Putative Association of a Single Nucleotide Polymorphism in GPR126 with Aggressive Periodontitis in a Japanese Population

Periodontitis is an inflammatory disease causing loss of tooth-supporting periodontal tissue. Disease susceptibility to the rapidly progressive form of periodontitis, aggressive periodontitis (AgP), appears to be influenced by genetic risk factors. To identify these in a Japanese population, we performed whole exome sequencing of 41 unrelated generalized or localized AgP patients. We found that AgP is putatively associated with single nucleotide polymorphism (SNP) rs536714306 in the G-protein coupled receptor 126 gene, GPR126 [c.3086 G>A (p.Arg1029Gln)]. Since GPR126 activates the cAMP/PKA signaling pathway, we performed cAMP ELISA analysis of cAMP concentrations, and found that rs536714306 impaired the signal transactivation of GPR126. Moreover, transfection of human periodontal ligament (HPDL) cells with wild-type or mutant GPR126 containing rs536714306 showed that wild-type GPR126 significantly increased the mRNA expression of bone sialoprotein, osteopontin, and Runx2 genes, while mutant GPR126 had no effect on the expression of these calcification-related genes. The increase in expression of these genes was through the GPR126-induced increase of bone morphogenic protein-2, inhibitor of DNA binding (ID) 2, and ID4 expression. These data indicate that GPR126 might be important in maintaining the homeostasis of periodontal ligament tissues through regulating the cytodifferentiation of HPDL cells. The GPR126 SNP rs536714306 negatively influences this homeostasis, leading to the development of AgP, suggesting that it is a candidate genetic risk factor for AgP in the Japanese population.

Bortezomib Inhibits Osteoclastogenesis and Porphyromonas gingivalis Lipopolysaccharide-induced Alveolar Bone Resorption

Healthy bone is maintained by the coordinated activities of osteoblast-mediated bone formation and osteoclast-dependent bone resorption. Pathologic conditions such as hormonal imbalance and inflammation cause increased osteoclastogenesis resulting in osteoporosis, rheumatoid arthritis, and periodontitis. Bortezomib is novel antimyeloma agent that has a direct beneficial effect on bone formation. However, the role of bortezomib in osteoclastogenesis and underlying mechanisms remains to be fully comprehended. In the present study, we show that bortezomib directly inhibited the receptor activator of nuclear factor κB ligand (RANKL)– and lipopolysaccharide-dependent osteoclast differentiation. Interestingly, the bortezomib-mediated inhibition of osteoclastogenesis was transient, since the removal of bortezomib from culture completely restored osteoclast differentiation. Bortezomib impeded the induction and nuclear localization of nuclear factor of activated T cells, cytoplasmic 1 and reduced both macrophage colony-stimulating factor– and RANKL-induced extracellular-signal-regulated kinase (ERK) phosphorylation. In a mouse model of periodontitis, bortezomib prevented alveolar bone erosion induced by Porphyromonas gingivalis lipopolysaccharide. These data not only suggest a previously unappreciated mechanism by which bortezomib regulates bone resorption but also propose novel applications of bortezomib beyond its use as an antimyeloma agent.

Human dental pulp stem cells: Applications in future regenerative medicine

Stem cells are pluripotent cells, having a property of differentiating into various types of cells of human body. Several studies have developed mesenchymal stem cells (MSCs) from various human tissues, peripheral blood and body fluids. These cells are then characterized by cellular and molecular markers to understand their specific phenotypes. Dental pulp stem cells (DPSCs) are having a MSCs phenotype and they are differentiated into neuron, cardiomyocytes, chondrocytes, osteoblasts, liver cells and β cells of islet of pancreas. Thus, DPSCs have shown great potentiality to use in regenerative medicine for treatment of various human diseases including dental related problems. These cells can also be developed into induced pluripotent stem cells by incorporation of pluripotency markers and use for regenerative therapies of various diseases. The DPSCs are derived from various dental tissues such as human exfoliated deciduous teeth, apical papilla, periodontal ligament and dental follicle tissue. This review will overview the information about isolation, cellular and molecular characterization and differentiation of DPSCs into various types of human cells and thus these cells have important applications in regenerative therapies for various diseases. This review will be most useful for postgraduate dental students as well as scientists working in the field of oral pathology and oral medicine.