Knockout of glutathione peroxidase 5 down-regulates the piRNAs in the caput epididymidis of aged mice

The mammalian epididymis not only plays a fun dame ntal role in the maturati on of spermatozoa,but also provides protecti on agai nst various stressors.The foremost among these is the threat posed by oxidative stress,which arises from an imbalance in reactive oxygen species and can elicit damage to cellular lipids,proteins,and nucleic acids.In mice,the risk of oxidative damage to spermatozoa is mitigated through the expression and secretion of glutathione peroxidase 5(GPX5)as a major luminal scavenger in the proximal caput epididymidal segment.Accordingly,the loss of GPX5^-/-mediated protection leads to impaired DNA integrity in the spermatozoa of aged Gpx57 mice.To explore the underlying mechanism,we have conducted transcriptomic analysis of caput epididymidal epithelial cells from aged(13 months old)Gpx5^-/-m mice.This analysis revealed the dysregulation of several thousand epididymal mRNA transcripts,in eluding the downregulation of a subgroup of piRNA pathway gen es,in aged Gpx5^-/-mice.In agreeme nt with these fin dings,we also observed the loss of piRNAs,which potentially bind to the P-element-induced wimpy testis(PlWI)-like proteins PIWIL1 and PIWIL2.The absence of these piRNAs was correlated with the elevated mRNA levels of their putative gene targets in the caput epididymidis of Gpx5^-/-mice.Importantly,the oxidative stress response genes tend to have more targeting piRNAs,and many of them were among the top increased genes upon the loss of GPX5^-/-.Taken together,our findings suggest the existence of a previously uncharacterized somatic piRNA pathway in the mammalian epididymis and its possible invoIvement in the aging and oxidative stress-mediated responses.

Resin Matrix Shear Band and Its Special Effect on Stress Concentration of Fiber Composites

A constitutive model is constructed to consider the resin matrix post-yield softening and progressive hardening behaviors. A user-defined material mechanical behavior （UMAT） subroutine is created, then the non-linear three-dimensional finite element analysis on the tensile processes of multi-fiber composites is conducted. The approximate 45° shear bands emanating from the matrix crack tip are found, being coincided with the experimental observations. The shear stress on the adjacent intact fiber/matrix interface is strongly influenced by the shear band and thus the stress concentration factor （SCF） changes obviously in the adjacent fibers. The distinct stress redistribution in the adjacent intact fibers implies the significant effect of the shear bands on the progressive fiber fracture initiation. As the inter-fiber spacing increases, the peak value of the SCF in the adjacent intact fiber decreases, whereas the overload zone becomes wider. The research has provided a helpful tool to evaluate the failure of fiber composites and optimize the composite performance through the proper selection of resin matrix properties and fiber volume fraction.