Severe acute respiratory syndrome (SARS) is a respiratory disease, caused by a coronavirus (SARS-CoV), that is characterized by atypical pneumonia. The nucleocapsid protein (N protein) of SARS-CoV plays an important role in inhibition of type I interferon (IFN) production via an unknown mechanism. In this study, the SARS-CoV N protein was found to bind to the SPRY domain of the tripartite motif protein 25 (TRIM25) E3 ubiquitin ligase, thereby interfering with the association between TRIM25 and retinoic acid-inducible gene I (RIG-I) and inhibiting TRIM25-mediated RIG-I ubiquitination and activation. Type I IFN production induced by poly I·C or Sendai virus (SeV) was suppressed by the SARS-CoV N protein. SARS-CoV replication was increased by overexpression of the full-length N protein but not N amino acids 1 to 361, which could not interact with TRIM25. These findings provide an insightful interpretation of the SARS-CoV-mediated host innate immune suppression caused by the N protein.IMPORTANCE The SARS-CoV N protein is essential for the viral life cycle and plays a key role in the virus-host interaction. We demonstrated that the interaction between the C terminus of the N protein and the SPRY domain of TRIM25 inhibited TRIM25-mediated RIG-I ubiquitination, which resulted in the inhibition of IFN production. We also found that the Middle East respiratory syndrome CoV (MERS-CoV) N protein interacted with TRIM25 and inhibited RIG-I signaling. The outcomes of these findings indicate the function of the coronavirus N protein in modulating the host's initial innate immune response.
Mesenchymal stem cells (MSCs) are ideal seed cells for bone tissue engineering. However, intrinsic deficiencies exist for the autologous transplantation strategy of constructing artificial bone with MSCs derived from bone marrow of patients. In this study, MSCs-like cells were isolated from human umbilical cords and were expanded in vitro. Flow cytometric analysis revealed that cells from the fourth passage were positive for CD29, CD44, CD71, CD73, CD90, and CD105 whereas they were negative for CD14, CD34, CD45, and CD117. Furthermore, these cells expressed HLA-A, B, C (MHC-I), but not HLA-DP, DQ, DR (MHC-II), or costimulatory molecules such as CD80 and CD86. Following incubation in specific inductive media for 3 weeks, cultured cells were shown to possess potential to differentiate into adipogenic, osteogenic or chondrogenic lineages in vitro. The umbilical cord-derived MSCs (UC-MSCs) were loaded with a biomimetic artificial bone scaffold material before being implanted subcutaneously in the back of Balb/c nude mice for four to twelve weeks. Our results revealed that UC-MSCs loaded with the scaffold displayed capacity of osteogenic differentiation leading to osteogenesis with human origin in vivo. As a readily available source of seed cells for bone tissue engineering, UC-MSCs should have broad application prospects.
Numerous studies have demonstrated the capacity of mechanical strains to modulate cell behavior through several different signaling pathways. Understanding the response of ligament fibroblasts to mechanically induced strains may provide useful knowledge for treating ligament injury and improving rehabilitation regimens. Biomechanical studies that quantify strains in the anterior cruciate and medial collateral ligaments have shown that these ligaments are subjected to 4-5% strains during normal activities and can be strained to 7.7% during external application of loads to the knee joint. The objective of this study was to characterize the expression of types I and I11 collagen in fibroblast monolayers of anterior cruciate and medial collateral ligaments subjected to equibiaxial strains on flexible growth surfaces (0.05 and 0.075 strains) by quantifying levels of mRNA encoding these two proteins. Both cyclic strain magnitudes were studied under a frequency of 1 Hz. The results indicated marked differences in responses to strain regimens not only between types I and I11 collagen mRNA expression within each cell type but also in patterns of expression between anterior cruciate and medial collateral ligament cells. Whereas anterior cruciate ligament fibroblasts responded to cyclic strains by expression of higher levels of type-I collagen message with almost no significant increases in type-I11 collagen, medial collateral ligament fibroblasts exhibited statistically significant increases in type-111 collagen mRNA at all time points after initiation of strain with almost no significant increases in type-I collagen. Furthermore, differences in responses by fibroblasts from the two ligaments were detected between the two strain magnitudes. In particular, 0.075 strains induced a time-dependent increase in type-I11 collagen mRNA levels in medial collateral ligament fibroblasts whereas 0.05 strains did not. The strain-induced changes in gene expression of these two collageiis may have implications for the healing processes in ligament tissue. The differences may explain, in part, the healing differential between the anterior cruciate and medial collateral ligaments in vivo.
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