Mechanisms underlying the inhibition of chondrocyte apoptosis and inflammatory cytokine expression in knee osteoarthritis by rehmannia glutinosa polysaccharides via PI3K/AKT pathway activation at different concentrations.
Abstract
Background
Knee osteoarthritis (KOA) is a persistent articular disorder primarily defined by cartilage degradation and inflammatory response, where chondrocyte apoptosis serves as a critical pathological mechanism.
Objective
This work aimed to investigate the effects of rehmannia glutinosa polysaccharides (RGP) on interleukin-1β (IL-1β)-induced apoptosis and inflammation in KOA chondrocytes, and to elucidate its relationship with the PI3K/AKT pathway.
Methods
An in vitro injury model was established by inducing human knee osteoarthritis (KOA) chondrocytes with IL-1β. The cells were divided into a control group, a model group, low-, medium-, and high-dose RGP groups, and a high-dose RGP + LY294002 group. The evaluated parameters included cell viability (CCK-8 assay), apoptosis (Caspase-3 activity and TUNEL staining), inflammatory cytokines (IL-1β, IL-6, TNF-α; mRNA levels detected by qRT-PCR), and PI3K/AKT/mTOR pathway activity (AKT, p-AKT, mTOR, p-mTOR; as well as Bax, Bcl-2, and cleaved PARP detected by Western blot).
Results
Compared with the model group, RGP improved cell viability, inhibited Caspase-3 activity, and reduced the apoptosis index as well as the levels of inflammatory cytokines at both the protein and mRNA levels in a dose-dependent manner. Moreover, RGP significantly upregulated p-AKT and p-mTOR, increased Bcl-2 expression, decreased Bax and cleaved PARP expression, and elevated the Bcl-2/Bax ratio, without affecting total AKT or mTOR. LY294002 completely abolished these effects. The p-AKT/AKT ratio was significantly negatively correlated with apoptosis and inflammation.
Conclusion
Rehmannia glutinosa polysaccharide (RGP) exerts a protective effect on cartilage by activating the PI3K/AKT/mTOR signaling pathway to regulate the mitochondrial apoptosis pathway, thereby inhibiting IL-1β-induced apoptosis and inflammatory responses in knee osteoarthritis chondrocytes.