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PARK7 (DJ1) is a multifunctional oxidative stress response protein that protects cells against reactive oxygen species (ROS) and mitochondrial damage. PARK7 defects are known to cause various physiological dysfunctions, including infertility. Asthenozoospermia (AS), i.e. low-motile spermatozoa in the ejaculate, is a common cause of human male infertility. In this study, we found that downregulation of PARK7 resulted in increased levels of lipid peroxide and ROS, decreased mitochondrial membrane potential, and reduced mitochondrial complex I enzyme activity in the spermatozoa from AS patients. Furthermore, it was observed that PARK7 was translocated into the mitochondria of damaged spermatozoa in AS. Finally, we examined the oxidative state of PARK7 and the results demonstrated the enhancement of oxidation, expressed by increased sulfonic acid residues, the highest form of oxidation, as the sperm motility decreased. Taken together, these results revealed that PARK7 deficiency may increase the oxidative stress damage to spermatozoa. Our present findings open new avenues of therapeutic intervention targeting PARK7 for the treatment of AS.

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In this paper, we present an application-oriented investigation of parasitic limitation on the large signal performance of VCSELs when multilevel modulation is applied. VCSELs with different damping are taken into consideration. The parasitic parameters are extracted by fitting the measured S 11 data toward a frequency of 40 GHz. In the large signal analysis, four-level pulse amplitude modulation (PAM-4) signaling is embedded into the tool of VCSEL integrated spatio-temporal advanced simulator (VISTAS) and analyzed with extracted parameters. The transmitter and dispersion eye closure quaternary (TDECQ) of the 50-Gb/s PAM-4 signals from VCSEL model is evaluated to understand the relationship between parasitic parameters and signal quality. It is found that the over-damped VCSEL would benefit from larger parasitic bandwidth for PAM-4 modulation while the under-damped VCSEL with moderate parasitic bandwidth would present the best large signal response for PAM-4 modulation. The results indicate that for multilevel modulation, the parasitic parameters need to be carefully designed according to the VCSEL intrinsic parameters to achieve better large signal performance. By co-optimizing the key parasitic parameters, the parasitic circuit design criteria for each type of VCSEL are provided to obtain the best large signal performance under multilevel modulation. The results could provide a designing guidance for VCSELs aiming at multilevel modulation applications.