3.1 Effects on MAPK signaling pathway The mitogen-activated protein kinase (MAPK) signaling pathway is an important signal transduction system in the body, mediating various physiological and pathological processes such as cell growth, development, differentiation and apoptosis. The main families are ERK, JNK, p38. In the nervous system, the increased activity of ERK mediates the proliferation and differentiation of most neuronal cells. The activated ERK has anti-apoptotic activity. The activation of JNK and p38 is mainly reflected in astrocytes and microglia. Stress and apoptosis are necessary, and activation has a pro-apoptotic effect, thereby affecting the expression of the lower cascade signaling factors Bcl-2, Bax, Caspase-9, and Caspase-3, mediating apoptosis and inflammatory responses.
Studies have shown that PF intervention can protect against TNF-α-induced apoptosis and neuronal loss, and this protective effect of PF may be achieved by inhibiting MAPK/NF-κB-mediated ischemic injury-induced peripheral and brain inflammatory responses of. Zhou et al. found that PF (20, 40, 60 mg/kg) could significantly reduce the expression of p-p38 and p-JNK protein levels in a neuropathic pain rat model, and at the same time reduce the levels of inflammatory factors IL-1 and TNF-α. This effect may be achieved by inhibiting the expression of upstream signal ASK1 and then inhibiting p38 and JNK. Zhong et al. found that PF (30 mg/kg and 60 mg/kg) could increase the expression of p-ERK protein level in a rat model of chronic unpredictable stress disorder, indicating that PF could play a neuroprotective role by regulating ERK signaling pathway.
3.2 Influence on PI3K/Akt signaling pathway PI3K/Akt signaling pathway mediates cell reproduction, differentiation, apoptosis and other reactions, and it has many downstream effectors, among which Akt is the central link of this signal transduction. Akt activation acts on the downstream Bcl-2 family, Caspase family, NF-κB family, etc. The activation of PI3K/Akt signaling pathway can increase the expression of anti-apoptotic protein Bcl-2, and reduce the expression of pro-apoptotic proteins Caspase and Bax. Studies have shown that PF may upregulate Bcl-2 and downregulate the protein expression levels of Caspase-9, Caspase-3 and Bax by activating the PI3K/Akt pathway, thereby protecting neurons from apoptosis. Pretreatment with PF (50-400 mg/L) can increase the protein levels of p-PI3K and p-Akt-1 in neural progenitor cells with H2O2-induced injury, and this effect of PF can be abolished by the PI3K inhibitor LY294002, indicating that PF is mediated by PF. The neuroprotective effect of H2O2 injury depends on the activation of PI3K/Akt-1 pathway.
3.3 Activation of Nrf2/ARE signaling pathway Oxidative stress is an important factor in the initiation and development of many neurodegenerative diseases, and Nrf2/ARE signaling pathway is a key pathway in cellular oxidative stress response. When oxidative stress occurs, Nrf2 dissociates from Keap1, translocates into the nucleus, and binds to antioxidant response elements (AREs) to promote the gene expression of detoxification enzymes and antioxidant enzymes, playing an important role in cellular defense protection.
Nrf2 plays a crucial role in maintaining normal physiological processes in the brain. Nrf2 knockout in mice results in proteasome dysfunction, neuronal apoptosis, age-related forebrain atrophy, and neurobehavioral deficits. PF (10, 50, 100 μmol/L) can promote the expression of Nrf2 protein in the brain tissue of rats with cerebral ischemia-reperfusion injury, and also promote the transfer of Nrf2 from the cytoplasm to the nucleus in PC12 cells in a dose-dependent manner. Knockdown of Nrf2 by siRNA attenuated the protective effect of PF in PC12 cells, and found that its antioxidant and anti-inflammatory activities were weakened, suggesting that PF may regulate the expression of genes related to antioxidant response elements by promoting the expression and activation of Nrf2, thereby reducing cerebral ischemia and reactivation. Exhibits antioxidant and anti-inflammatory effects after perfusion injury.