Endochondral ossification is initiated by the differentiation of mesenchymal precursor cells to chondrocytes (chondrogenesis). This process is characterized by a strong interdependence of cell shape, cytoskeletal organization, and the onset of chondrogenic gene expression, but the molecular mechanisms mediating these interactions are not known. Here we investigated the role of the RhoA/ROCK pathway, a well characterized regulator of cytoskeletal organization, in chondrogenesis. We show that pharmacological inhibition of ROCK signaling by Y27632 resulted in increased glycosaminoglycan synthesis and elevated expression of the chondrogenic transcription factor Sox9, whereas overexpression of RhoA in the chondrogenic cell line ATDC5 had the opposite effects. Suppression of Sox9 expression by ROCK signaling was achieved through repression of Sox9 promoter activity. These molecular changes were accompanied by reorganization of the actin cytoskeleton, where RhoA/ROCK signaling suppressed cortical actin organization, a hallmark of differentiated chondrocytes. This led us to analyze the regulation of Sox9 expression by drugs affecting cytoskeletal dynamics. Both inhibition of actin polymerization by cytochalasin D and stabilization of existing actin filaments by jasplakinolide resulted in increased Sox9 mRNA levels, whereas inhibition of microtubule polymerization by colchicine completely blocked Sox9 expression. In conclusion, our data suggest that RhoA/ROCK signaling suppresses chondrogenesis through the control of Sox9 expression and actin organization.

Chondrocyte differentiation is a multi-step process characterized by successive changes in cell morphology and gene expression. In addition to tight regulation by numerous soluble factors, these processes are controlled by adhesive events. During the early phase of the chondrocyte life cycle, cell-cell adhesion through molecules such as N-cadherin and neural cell adhesion molecule (N-CAM) is required for differentiation of mesenchymal precursor cells to chondrocytes. At later stages, for example in growth plate chondrocytes, adhesion signaling from extracellular matrix (ECM) proteins through integrins and other ECM receptors such as the discoidin domain receptor (DDR) 2 (a collagen receptor) and Annexin V is necessary for normal chondrocyte proliferation and hypertrophy. Cell-matrix interactions are also important for chondrogenesis, for example through the activity of CD44, a receptor for Hyaluronan and collagens. The roles of several signaling molecules involved in adhesive signaling, such as integrin-linked kinase (ILK) and Rho GTPases, during chondrocyte differentiation are beginning to be understood, and the actin cytoskeleton has been identified as a common target of these adhesive pathways. Complete elucidation of the pathways connecting adhesion receptors to downstream effectors and the mechanisms integrating adhesion signaling with growth factor-and hormone-induced pathways is required for a better understanding of physiological and pathological skeletal development.

Medical Internet of Things, also well known as MIoT, is playing a more and more important role in improving the health, safety, and care of billions of people after its showing up. Instead of going to the hospital for help, patients' health-related parameters can be monitored remotely, continuously, and in real time, then processed, and transferred to medical data center, such as cloud storage, which greatly increases the efficiency, convenience, and cost performance of healthcare. The amount of data handled by MIoT devices grows exponentially, which means higher exposure of sensitive data. The security and privacy of the data collected from MIoT devices, either during their transmission to a cloud or while stored in a cloud, are major unsolved concerns. This paper focuses on the security and privacy requirements related to data flow in MIoT. In addition, we make in-depth study on the existing solutions to security and privacy issues, together with the open challenges and research issues for future work.

Coordinated proliferation and differentiation of growth plate chondrocytes is required for normal growth and development of the endochondral skeleton, but little is known about the intracellular signal transduction pathways regulating these processes. We have investigated the roles of the GTPase RhoA and its effector kinases ROCK1/2 in hypertrophic chondrocyte differentiation. RhoA, ROCK1, and ROCK2 are expressed throughout chondrogenic differentiation. RhoA overexpression in chondrogenic ATDC5 cells results in increased proliferation and a marked delay of hypertrophic differentiation, as shown by decreased induction of alkaline phosphatase activity, mineralization, and expression of the hypertrophic markers collagen X, bone sialoprotein, and matrix metalloproteinase 13. These effects are accompanied by activation of cyclin D1 transcription and repression of the collagen X promoter by RhoA. In contrast, inhibition of Rho/ROCK signaling by the pharmacological inhibitor Y27632 inhibits chondrocyte proliferation and accelerates hypertrophic differentiation. Dominant-negative RhoA also inhibits induction of the cyclin D1 promoter by parathyroid hormone-related peptide. Finally, Y27632 treatment partially rescues the effects of RhoA overexpression. In summary, we identify the RhoA/ROCK signaling pathway as a novel and important regulator of chondrocyte proliferation and differentiation.The development and growth of endochondral bones (such as ribs, vertebrae, and the long bones of vertebrate limbs) are regulated through the highly controlled rates of proliferation and hypertrophic differentiation of growth plate chondrocytes (1-3). In the growth plate, chondrocytes first undergo a series of cell divisions along the longitudinal axis of the growing bone, thereby forming characteristic columns of clonal cells. Chondrocytes then withdraw from the cell cycle and begin to increase their cell volume until reaching the fully differentiated state of hypertrophic chondrocytes. Transition from a proliferating to a hypertrophic phenotype involves numerous changes in gene expression, for example the induction of the collagen X (4, 5), matrix metalloproteinase 13 (6, 7), and bone sialoprotein (BSP) 1 (8 -10) genes. The latter two genes are also expressed by osteoblasts, suggesting similar biological properties of hypertrophic chondrocytes and osteoblasts. The fate of hypertrophic chondrocytes is still debated, but it appears that the majority of these cells undergo apoptosis and are replaced by bone tissue (11). Longitudinal growth of endochondral bones therefore requires both proliferation and differentiation-associated hypertrophy of growth plate chondrocytes.Disruption of chondrocyte proliferation and/or differentiation by gene mutations commonly results in chondrodysplasias that are characterized by skeletal deformities and reduced growth (12)(13)(14). Mutations in genes encoding extracellular matrix molecules, growth factors, receptors, and transcription factors have been identified as causes of several chondrodysplasias. Fo...

Small GTPases of the Rho family have been implicated in the regulation of many intracellular processes. However, their tissue-specific roles in mammalian growth and development in vivo remain largely unknown. Here we describe the effects of cartilage-specific inactivation of the Rac1 gene in mice. Mice carrying this mutation show increased lethality, skeletal deformities, severe kyphosis and dwarfism. Rac1-deficient growth plates are disorganized and hypocellular, with chondrocytes of abnormal shape and size. Rac1-deficient chondrocytes also display reduced adhesion and spreading on collagen II and fibronectin as well as altered organization of the actin cytoskeleton, suggesting that Rac1 is required for normal cell-extracellular matrix interactions in cartilage. This phenotype is accompanied by reduced proliferation, increased apoptosis and deregulated expression of the cell cycle genes cyclin D1 and p57 in vivo. Moreover, phosphorylation of p38 MAP kinases is greatly reduced and expression of a key regulator of cartilage development, Indian hedgehog, is increased in mutant mice. In summary, these data identify a novel, essential and tissue-specific role of Rac1 in skeletal development and demonstrate that Rac1 deficiency affects numerous regulatory pathways in cartilage.