The essential role of Mkx in periodontal ligament on the metabolism of alveolar bone and cementum.

Introduction: The periodontium is a connective tissue which consists of periodontal ligament, alveolar bone, cementum and gingiva. Periodontal ligament (PDL) is a specialized connective tissue that connects the cementum - coating the surface of the tooth - to the alveolar bone. Mohawk homeobox (Mkx) is a transcription factor that is expressed in PDL, that is known to play a vital role in the development and homeostasis of PDL. A detailed functional analysis of Mkx in the periodontal ligament for alveolar bone and cementum metabolism has not yet been conducted. Materials and methods: Alveolar bone height, bone mineral density (BMD) and bone volume fractions (Bone volume/Total volume: BV/TV) were measured and analyzed using micro-computed tomography (Micro-CT) and 3DBon on 7-week-old male wild-type (WT) (Mkx+/+) (n = 10) and Mkx-knockout (Mkx-/-) (n = 6) rats. Hematoxylin and Eosin (H&E), tartrate-resistant acid phosphatase (TRAP), alkaline phosphatase (ALP) and Masson Trichrome staining were performed on 5, 6, and 7-week-old Mkx+/+ and Mkx-/- rats. Cementum surface area and the number of TRAP-positive osteoclasts/mm were quantified, measured, and compared for 5,6 and 7-week-old Mkx+/+ and Mkx-/- rats (n = 3 each). Results: The level of alveolar bone height was significantly higher in Mkx-/- rats than in Mkx+/+ rats. On the other hand, there was significantly less BMD in Mkx-/- alveolar bone. A significant increase in cellular cementum could be observed as early as 5 weeks in Mkx-/- rats when compared with Mkx+/+ rats of the same age. More TRAP-positive osteoclasts were observed in Mkx-/- rats. Conclusion: Our findings further reveal the essential roles of Mkx in the homeostasis of the periodontal tissue. Mkx was found to contribute to bone and cementum metabolism and may be essential to the prevention of diseases such as periodontitis, and could show potential in regenerative treatments.

Cartilage Homeostasis and Osteoarthritis.

Healthy limb joints are important for maintaining health and attaining longevity. Endochondral ossification (the replacement of cartilage with bone, occurring during skeletal development) is essential for bone formation, especially in long-axis bones. In contrast to endochondral ossification, chondrocyte populations in articular cartilage persist and maintain joint tissue into adulthood. Articular cartilage, a connective tissue consisting of chondrocytes and their surrounding extracellular matrices, plays an essential role in the mechanical cushioning of joints in postnatal locomotion. Osteoarthritis (OA) pathology relates to disruptions in the balance between anabolic and catabolic signals, that is, the loss of chondrocyte homeostasis due to aging or overuse of cartilages. The onset of OA increases with age, shortening a person's healthy life expectancy. Although many people with OA experience pain, the mainstay of treatment is symptomatic therapy, and no fundamental treatment has yet been established. To establish regenerative or preventative therapies for cartilage diseases, further understanding of the mechanisms of cartilage development, morphosis, and homeostasis is required. In this review, we describe the general development of cartilage and OA pathology, followed by a discussion on anabolic and catabolic signals in cartilage homeostasis, mainly microRNAs.

Single Cell RNA Sequencing Reveals Critical Functions of Mkx in Periodontal Ligament Homeostasis.

The periodontal ligament (PDL) comprises a fibrous tissue that connects teeth to alveolar bone and is essential for periodontal function. The transcription factor mohawk homeobox (Mkx) is expressed in the PDL where it plays an important role in the development and maintenance of the PDL. However, the precise and critical functions of Mkx in the cell populations comprising PDL have not yet been elucidated. The present study aimed to clarify the effects of a Mkx deficiency on PDL cellular heterogeneity and differences between gene expression in PDL tissues from wild-type (WT) (Mkx +/+ ) and Mkx knockout (Mkx -/- ) rats using single-cell RNA sequencing. We identified 12 cell clusters comprising mesenchymal cells and macrophages. The expression of Mkx and scleraxis (Scx; another key transcription factor of PDL), was mutually exclusive, and partitioned mesenchymal cell clusters into Mkx and Scx types that dominantly expressed proteoglycans and elastic fibers, and type 1 and 3 collagen, respectively. Ossification-related genes were upregulated in mesenchymal cell and osteoblast clusters with more Mkx -/- than Mkx +/+ PDLs. Increased number of cells and inflammatory mediators were observed in macrophage clusters of Mkx -/- PDL. These results suggested that Mkx plays an important role in maintaining PDL homeostasis by regulating specific cell populations and gene expression.

Mkx regulates the orthodontic tooth movement via osteoclast induction.

INTRODUCTION: The periodontal ligament (PDL) plays an important role in orthodontic tooth movement; however, the underlying molecular mechanism remains unclear. We have previously reported that the Mohawk homeobox (Mkx), a tendon-specific transcription factor, is expressed in the PDL and regulates its homeostasis. MATERIALS AND METHODS: In the present study, we examined the role of Mkx in orthodontic tooth movement via bone remodeling induced by mechanical stimulation in Mkx-deficient rats, which are widely used as experimental animals for orthodontic force application. Orthodontic tooth movement of the maxillary first molar was performed in 7-week-old male Mkx-deficient rats (n = 4) and wild-type Wistar rats (n = 4) using coil springs for 14 days. Hematoxylin and eosin (H&E) staining and tartrate-resistant acid phosphatase (TRAP) staining were performed to evaluate morphological changes and osteoclasts. Furthermore, changes in the expression of receptor activator nuclear factor-kappa B ligand (RANKL) were demonstrated using immunostaining. RESULTS: The amount of tooth movement was significantly lower in Mkx-deficient rats than in wild-type rats. The number of TRAP-positive cells was suppressed in Mkx-deficient rats on the compression side. CONCLUSION: Orthodontic tooth movement experiments in Mkx-deficient rats suggested that Mkx is involved in osteoclast induction at the alveolar bone surface on the compression side. This study reveals the possibility that Mkx plays a mechanosensory role in orthodontic tooth movement by inducing RANKL expression and osteoclastogenesis.

Generation of pluripotent stem cells from patients with type 1 diabetes.

Type 1 diabetes (T1D) is the result of an autoimmune destruction of pancreatic beta cells. The cellular and molecular defects that cause the disease remain unknown. Pluripotent cells generated from patients with T1D would be useful for disease modeling. We show here that induced pluripotent stem (iPS) cells can be generated from patients with T1D by reprogramming their adult fibroblasts with three transcription factors (OCT4, SOX2, KLF4). T1D-specific iPS cells, termed DiPS cells, have the hallmarks of pluripotency and can be differentiated into insulin-producing cells. These results are a step toward using DiPS cells in T1D disease modeling, as well as for cell replacement therapy.