Ensemble structural analyses depict the regulatory mechanism of non-phosphorylated human MAP2K4

Quantitative phosphoproteomics explain cryopreservation-induced reductions in ram sperm motility

Sperm cryopreservation decreases motility, probably due to changes in protein phosphorylation. Our objective was to use quantitative phosphoproteomics for systematic comparative analyses of fresh versus frozen-thawed sperm to identify factors causing cryo-injury. Ejaculates were collected (artificial vagina) from six Dorper rams, pooled, extended, and frozen over liquid nitrogen. Overall, 915, 3382, and 6875 phosphorylated proteins, phosphorylated peptides, and phosphorylation sites, respectively, were identified. At least two modified sites were present in 57.94% of the 6875 phosphosites identified, of which AKAP4 protein contained up to 331 modified sites. There were 732 phosphorylated peptides significantly up-regulated and 909 significantly down-regulated in frozen-thawed versus fresh sperm. Moreover, the conserved motif [RxxS] was significantly down-regulated in frozen-thawed sperm. Phosphorylation of sperm-specific proteins, e.g., AKAP3/4, CABYR, FSIP2, GSK3A/B, GPI, and ODF1/2 make them potential biomarkers to assess the quality of frozen-thawed ram sperm. Furthermore, these differentially phosphorylated proteins and modification sites were implicated in cryopreservation-induced changes in sperm energy production, fiber sheath composition, and various biological processes. We concluded that abnormal protein phosphorylation modifications are key regulators of reduced sperm motility. These novel findings implicated specific protein phosphorylation modifications in sperm cryo-injury. SIGNIFICANCE: This study used phosphorylated TMT quantitative proteomics to explore regulation of epigenetic modifications in frozen-thawed ram sperm. This experiment demonstrated that ram sperm freezing affects phosphorylation site modifications of proteins, especially those related to functions such as sperm motility and energy production. Furthermore, it is important to link functions of phosphorylated proteins with changes in sperm quality after freezing and thawing, and to clarify intrinsic reasons for sperm quality changes, which is of great importance for elucidating mechanisms of sperm freezing damage. Based on these protein markers and combined with cryoprotectant design theory, it provides a theoretical basis and data reference to study sperm cryoprotectants.

Enhancing the correlation between in vitro and in vivo experiments in dental implant osseointegration: investigating the role of Ca ions

This study delves into the osteogenic potential of a calcium-ion modified titanium implant surface, unicCa, employing state-of-the-art proteomics techniques both in vitro (utilizing osteoblasts and macrophage cell cultures) and in vivo (in a rabbit condyle model). When human osteoblasts (Hobs) were cultured on unicCa surfaces, they displayed a marked improvement in cell adhesion and differentiation compared to their unmodified counterparts. The proteomic analysis also revealed enrichment in functions associated with cell migration, adhesion, extracellular matrix organization, and proliferation. The analysis also underscored the involvement of key signalling pathways such as PI3K-Akt and mTOR. In the presence of macrophages, unicCa initially exhibited improvement in immune-related functions and calcium channel activities at the outset (1 day), gradually tapering off over time (3 days). Following a 5-day implantation in rabbits, unicCa demonstrated distinctive protein expression profiles compared to unmodified surfaces. The proteomic analysis highlighted shifts in adhesion, immune response, and bone healing-related proteins. unicCa appeared to influence the coagulation cascade and immune regulatory proteins within the implant site. In summary, this study provides a comprehensive proteomic analysis of the unicCa surface, drawing correlations between in vitro and in vivo results. It emphasizes the considerable potential of unicCa surfaces in enhancing osteogenic behavior and immunomodulation. These findings significantly contribute to our understanding of the intricate molecular mechanisms governing the interplay between biomaterials and bone cells, thereby facilitating the development of improved implant surfaces for applications in bone tissue engineering.

FGF21 at physiological concentrations regulates vascular endothelial cell function through multiple pathways

Cardiovascular diseases are closely associated with dysfunction of vascular endothelial cells (VECs), which can be influenced by various intrinsic and extrinsic factors, including fibroblast growth factor 21 (FGF21), but the effects of serum FGF21 on VECs remain unclear. We performed a cross-sectional study nested within a prospective cohort to assess the range of physiological concentrations of fasting serum FGF21 in 212 healthy individuals. We also treated human umbilical VECs (HUVECs) with recombinant FGF21 at different concentrations. The effects of FGF21 treatment on glycolysis, nitric oxide release and reduction of intracellular reactive oxygen species were assessed. The cells were also collected for RNA transcriptomic sequencing to investigate the potential mechanisms induced by FGF21 treatment. In addition, the roles of SIRT1 in the regulation of FGF21 were evaluated by SIRT1 knockdown. The results showed that the serum FGF21 concentration in healthy individuals ranged from 15.70 to 499.96 pg/mL and was positively correlated with age and pulse wave velocity. FGF21 at 400 pg/mL was sufficient to enhance glycolysis, increase nitric oxide release and protect cells from H₂O₂-induced oxidative damage. The upregulated genes after FGF21 treatment were mostly enriched in metabolic pathways, whereas the downregulated genes were mostly enriched in inflammation and apoptosis signaling pathways. Moreover, SIRT1 may be involved in the regulation of some genes by FGF21. In conclusion, our data indicate that FGF21 at a level within the physiological concentration range has a beneficial effect on HUVECs and that this effect may partly depend on the regulation of SIRT1.

The autoinhibited state of MKK4: Phosphorylation, putative dimerization and R134W mutant studied by molecular dynamics simulations

Protein kinases are crucial components of the cell-signalling machinery that orchestrate and convey messages to their downstream targets. Most often, kinases are activated upon a phosphorylation to their activation loop, which will shift the kinase into the active conformation. The Dual specificity mitogen-activated protein kinase kinase 4 (MKK4) exists in a unique conformation in its inactive unphosphorylated state, where its activation segment appears in a stable α-helical conformation. However, the precise role of this unique conformational state of MKK4 is unknown. Here, by all-atom molecular dynamics simulations (MD simulations), we show that this inactive state is unstable as monomer even when unphosphorylated and that the phosphorylation of the activation segment further destabilizes the autoinhibited α-helix. The specific phosphorylation pattern of the activation segment has also a unique influence on MKK4 dynamics. Furthermore, we observed that this specific inactive state is stable as a dimer, which becomes destabilized upon phosphorylation. Finally, we noticed that the most frequent MKK4 mutation observed in cancer, R134W, which role has not been disclosed to date, contributes to the dimer stability. Based on these data we postulate that MKK4 occurs as a dimer in its inactive autoinhibited state, providing an additional layer for its activity regulation.