Multi-kinase-mediated alterations in Tau phosphorylation, synaptic proteins, and choline metabolism in a human...

Elastin, a key component of the extracellular matrix (ECM), undergoes degradation during aging, leading to the release of shorter bioactive fragments - among which the VGVAPG hexapeptide exhibits the highest biological activity. Although associated with aging-related neurodegeneration, the role of VGVAPG in this context has not been thoroughly investigated. Therefore, this study aimed to assess the effects of VGVAPG on Tau phosphorylation, synaptic proteins, choline metabolism, and the involvement of specific kinases in a human neuronal in vitro model, using selective inhibitors (Roscovitine, TDZD-8, SCH772984, SK1). All-trans retinoic acid (RA) and brain-derived neurotrophic factor (BDNF)-differentiated SH-SY5Y cells were employed due to their well-characterized neuronal phenotype and established utility in screening studies. Our results indicate that VGVAPG-induced signaling is mediated via SRC kinase, likely leading to activation of the RAS-RAF-ERK1/2-ELK1 pathway. This cascade results in increased CDK5 protein expression and elevated CIP2A levels, which may, in turn, inhibit PP2A function. Additionally, VGVAPG downregulated the PI3K-AKT pathway through PTEN activation, thereby relieving the inhibition of GSK3β. Consequently, we observed increased phosphorylation of Tau at S396, S404, S202/T205, and T231. Impairment of synaptic vesicle-associated proteins (SYN2, SNAP-25, SYP), along with alterations in ACh levels and AChE activity, appeared to be linked to ERK1/2 signaling, Tau accumulation, and potentially CDK5-dependent mechanisms. Overall, our findings provide novel insights into the possible contribution of the elastin-derived VGVAPG hexapeptide to the pathogenesis of aging-related neurodegeneration. While our model does not definitively confirm an AD-like phenotype, these results support the need for further investigation in more physiologically relevant systems.