Focus on seed cells: stem cells in 3D bioprinting of corneal grafts.

Corneal opacity is one of the leading causes of severe vision impairment. Corneal transplantation is the dominant therapy for irreversible corneal blindness. However, there is a worldwide shortage of donor grafts and consequently an urgent demand for alternatives. Three-dimensional (3D) bioprinting is an innovative additive manufacturing technology for high-resolution distribution of bioink to construct human tissues. The technology has shown great promise in the field of bone, cartilage and skin tissue construction. 3D bioprinting allows precise structural construction and functional cell printing, which makes it possible to print personalized full-thickness or lamellar corneal layers. Seed cells play an important role in producing corneal biological functions. And stem cells are potential seed cells for corneal tissue construction. In this review, the basic anatomy and physiology of the natural human cornea and the grafts for keratoplasties are introduced. Then, the applications of 3D bioprinting techniques and bioinks for corneal tissue construction and their interaction with seed cells are reviewed, and both the application and promising future of stem cells in corneal tissue engineering is discussed. Finally, the development trends requirements and challenges of using stem cells as seed cells in corneal graft construction are summarized, and future development directions are suggested.

Gene expression analysis during recovery process indicates the mechanism for innate immune injury and repair from Coxsackievirus B3-induced myocarditis.

To investigate the innate immune injury and repair mechanism during recovery from Coxsackievirus B3 (CVB3) induced myocarditis, we established an acute viral myocarditis recovery model by infecting BALB/c mice with CVB3. Histopathological examination of cardiac tissues after infection showed a gradual increase of myocardial injury to the maximum degree at 8 dpi (days post infection), followed by a recovery process with reduced viral replication. We also measured expression changes of innate immune genes in heart after 4, 8 and 12 days of infection using innate immune real-time PCR array. The results showed expression alterations in many Pattern Recognition Receptors (PRRs) genes upon CVB3 infection, which activated multiple important signaling pathways during recovery process. The expression of TLRs, RLRs, PKR and cytokines were strongly induced and reached the peak at 4 dpi in early myocarditis stage, followed by a gradual reduction in recovery stage, during which the levels were even lower than normal at 12 dpi. The strong correlation between cardiac histopathology score and chemokine expression level suggested that the chemokines might play a role in pathological changes during early myocarditis stage. In addition, we also found that both cell survival signaling pathways (AKT1, p38MAPK) and antiviral signaling pathways (IKKα/ß/ε) were activated and promoted the recovery during late myocarditis stage. Altogether, our observations improved the understanding of formation and progression of the pathological lesions, as well as the repair mechanism for acute viral myocarditis.

Coxsackievirus B3 2A protease promotes encephalomyocarditis virus replication.

To determine whether 2A protease of the enterovirus genus with type I internal ribosome entry site (IRES) effect on the viral replication of type II IRES, coxsackievirus B3(CVB3)-encoded protease 2A and encephalomyocarditis virus (EMCV) IRES (Type II)-dependent or cap-dependent report gene were transiently co-expressed in eukaryotic cells. We found that CVB3 2A protease not only inhibited translation of cap-dependent reporter genes through the cleavage of eIF4GI, but also conferred high EMCV IRES-dependent translation ability and promoted EMCV replication. Moreover, deletions of short motif (aa13-18 RVVNRH, aa65-70 KNKHYP, or aa88-93 PRRYQSH) resembling the nuclear localization signals (NLS) or COOH-terminal acidic amino acid motif (aa133-147 DIRDLLWLEDDAMEQ) of CVB3 2A protease decreased both its EMCV IRES-dependent translation efficiency and destroy its cleavage on eukaryotic initiation factor 4G (eIF4G) I. Our results may provide better understanding into more effective interventions and treatments for co-infection of viral diseases.