Purification and neuroprotective activity of MIP-16, a peptide derived from Morchella edulis
Parkinson’s disease (PD) is the second largest neurodegenerative disease in humans, with a prevalence rate of 2% to 3% among individuals aged 65 and above. The pathological characteristics of PD can be summarized as the loss of a large number of dopaminergic neurons in the substantia nigra pars compacta, leading to a decrease in dopamine biosynthesis in the substantia nigra and striatum. The pathogenic mechanism of PD is not yet clear. Studies have confirmed that environmental factors, genetic factors, oxidative stress, and other factors may be involved in the degeneration and death of dopaminergic neurons in PD. Among them, oxidative stress is an important cause of neuronal degeneration and degeneration. On the one hand, the brain is the organ with the highest oxygen consumption in normal physiological activities of humans, but the relative lack of antioxidant enzymes in the brain makes it very susceptible to oxidative stress damage; On the other hand, early studies have shown that an increase in mitochondrial oxidative stress in dopaminergic neurons in the substantia nigra pars compacta can trigger a dopamine dependent toxic cascade, leading to lysosomal dysfunction and accumulation of alpha synuclein, which are the two main pathological features of Parkinson’s disease. At present, classic dopamine replacement therapy is mostly used in medicine to treat PD, such as the supplementation of L-3,4-dihydroxyphenylalanine (L-DOPA). But more and more studies have found that this classic therapy has significant side effects. Clinical observations have found that long-term L-DOPA treatment has a certain probability of causing movement disorders in PD patients. Therefore, starting from reducing oxidative stress and seeking new neuroprotective agents is one of the potential ways to prevent and treat PD.
In recent years, the extraction and purification of neuroprotective agents with antioxidant activity from natural products have received widespread attention and significant progress has been made. The salidroside extracted from the roots of Rhodiola rosea L., a plant in the Sedaceae family, can inhibit oxidative stress and inflammation to protect apoptotic PC12 cells. Paeoniflorin alleviates 6-hydroxydopamine induced apoptosis in PC12 cells by inhibiting the activation of NF – κ B. However, compared to plants, there is relatively less research on fungal neuroprotective agents. Some fungal polysaccharides can exhibit good free radical scavenging activity and exert neuroprotective effects. However, fungal polysaccharides have a large molecular weight, complex structure, and are difficult to penetrate the blood-brain barrier, which limits their application as neuroprotective agents. The ethanol or water extracts of certain fungi contain neuroprotective factors, but the composition of the extracts is still unclear and the structure of the functional substances needs to be identified.
Morchella spp. is a precious edible and medicinal fungus, which is recorded in the Compendium of Materia Medica as “sweet and cold, non-toxic, phlegm resolving and qi regulating, and beneficial to the gastrointestinal tract”. Morchella importuna M. Kuo. is a widely cultivated variety in China. In our previous research, it was confirmed that the water extract of Morchella importuna contains a substance resembling nerve growth factor (NGF), which can promote the differentiation of PC12 cells and form neural networks. Based on this, this study further purified and identified the functional components in the fruiting body of Morchella prolifera, constructed a PC12 cell model damaged by 6-OHDA, verified the neuroprotective activity of the functional components in the fruiting body of Morchella prolifera, provided data for the development of the health benefits of artificially cultivated Morchella prolifera, and provided alternative resources for the screening of fungal derived neuroprotective agents.

Some large fungi have extremely high food and medicinal value, and are rich in protein, making them ideal raw materials for obtaining natural peptides. Cordymin is a peptide extracted from Cordyceps sinensis, which can inhibit inflammation and alleviate brain damage caused by ischemia and hypoxia in rats. The peptide PEMP isolated from the mycelium of Pleurotus eryngii has antioxidant, anti-tumor, and immune enhancing functions. At present, the active ingredients of fungi are mainly focused on the research of polysaccharides. Compared with fungal polysaccharides, peptides have a simple structure, low immunogenicity, and are easy to synthesize artificially, making them a highly promising part of modern drug development. At present, chromatographic column methods are often used to separate and purify polypeptides from protein hydrolysates, including ion exchange chromatography and/or gel filtration chromatography. The former can be separated according to the charge of ions and polar molecules, while the latter can be separated according to the molecular size. However, there are currently no reports on standard methods for extracting fungal peptides, and the pH value of the extraction buffer and whether protease hydrolysis is required during the extraction process have not been explored. In addition, extracting peptides from different types of fungi often corresponds to different extraction methods, which is not conducive to the promotion and application of fungal peptides. Compared to the standard extraction method for fungal polysaccharide maturity, further exploration is needed for the extraction method of fungal peptides. In this study, MIP-16 was purified using a combination of molecular exclusion chromatography and reverse high-performance liquid chromatography. The method first roughly divided the molecules based on their size, and then subdivided them based on their polarity. The experiment proved that this method has good discriminability, but the experimental time required is relatively long and further improvement is needed.
The degeneration and cell death of dopaminergic neurons in the substantia nigra striatum lead to dopamine deficiency, which is the main cause of Parkinson’s disease. Therefore, dopamine replacement therapy (such as supplementing L-DOPA) is currently one of the best methods for treating idiopathic Parkinson’s disease, which alleviates symptoms through the supplementation of exogenous dopamine. However, after the initial optimal treatment response period, long-term L-DOPA treatment often accompanies side effects such as loss of motor function. In addition, scholars have detected 6-OHDA in the urine of Parkinson’s disease patients who have been taking L-DOPA for a long time. Therefore, in this study, we treated PC12 cells with 6-OHDA to simulate the early occurrence of PD and search for new neuroprotective agents. In our study, we found that treatment with 6-OHDA increases the level of ROS in PC12 cells, which in turn triggers cell apoptosis. We speculate that long-term L-DOPA treatment may produce more 6-OHDA, which may have a negative feedback regulatory effect on the treatment of PD. Based on the above analysis, starting from reducing oxidative pressure and minimizing oxidative damage, it is expected to screen for efficient and safe neuroprotective agents. And the polysaccharides, peptides, triterpenes and other components contained in higher fungi have good antioxidant activity. Therefore, we are searching for neuroprotective agents from fungi to provide resources for drug screening in PD.
Oxidation reactions can provide energy for human life activities, but the superoxide anion radicals and hydroxyl radicals generated during the reaction can cause oxidative damage. The presence of endogenous antioxidant enzymes and other antioxidants tends to balance the production and consumption of ROS, maintaining a steady state under normal conditions. However, studies have found that as age increases, the efficiency of the antioxidant system gradually decreases. In the elderly population, the increase in reactive oxygen species exceeds the clearance capacity of the antioxidant system, leading to oxidative stress and potentially causing neurodegenerative diseases such as Parkinson’s disease. Endogenous antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH Px), etc., are the body’s natural defense system against oxidative stress. After treatment with 6-OHDA, the intracellular antioxidant enzyme activity significantly decreased. It can be inferred that at this time, the intracellular antioxidant enzyme system significantly exceeds the normal load. MIP-16 pretreatment for 6 hours significantly increased endogenous antioxidant enzyme activity in PC12 cells. SOD levels reflect the load of the intracellular antioxidant enzyme system and indirectly reflect the level of intracellular free radicals. This result may indicate that the generation of anionic superoxide was reduced after MIP-16 pretreatment. In addition, GSH Px is a core component of cellular antioxidant defense and an electron donor for ROS, suggesting that MIP-16, as another detoxification system, may affect GSH metabolism and avoid 6-OHDA induced cell death.
When the endogenous antioxidant enzyme system cannot clear ROS in a timely manner, ROS can easily damage biomolecules, ultimately leading to cell apoptosis. Bcl-2 and Bax are the most representative apoptosis inhibiting genes and apoptosis promoting genes in the Bcl-2 protein family, respectively. The Bax protein encoded by the Bax gene can form heterodimers with Bcl-2, inhibiting the expression of Bcl-2. Research has found that the ratio of Bax/Bcl-2 proteins is a key factor determining the strength of cell apoptosis inhibition, and Bax/Bcl-2 can also be considered as a molecular switch for apoptosis. The mechanism of Bax induced cell apoptosis is that Bax enters mitochondria under the action of tBid, increases the permeability of mitochondrial membrane, and then releases cytochrome C. The release of cytochrome C is a key step in the endogenous pathway of cell apoptosis, which occurs by targeting and activating Caspase-9, leading to the activation of effector caspases (such as Caspase-3). Therefore, this study investigated the protective effect of MIP-16 on 6-OHDA induced cell apoptosis by detecting the expression levels of Bcl-2 and Bax, as well as the activity of Caspase (Caspase-3 and Caspase-9). From our research, we observed that pretreatment of 6-OHDA with MIP-16 significantly increased Bcl-2 levels and decreased Bax levels, while inhibiting Caspase-3 and Caspase-9 activity. These results suggest that MIP-16 may exert anti apoptotic effects by regulating the Bcl-2/Bax ratio and inhibiting Caspase-3/-9 activity.
The research results indicate that MIP-16 has a significant inhibitory effect on 6-OHDA induced apoptosis in PC12 cells: reshaping endogenous antioxidant enzyme activity, including SOD, CAT, and GSH Px, as an endogenous antioxidant promoter. Reduce ROS levels and MDA production, thereby lowering cellular oxidation levels and inhibiting the initiation of apoptosis. Regulating the Bax/BCl-2 ratio, inhibiting the expression of Caspase-9 and Caspase-3, thereby blocking the mitochondrial apoptosis pathway in cells. MIP-16 has a simple structure and is easy to synthesize artificially, which is expected to be developed and utilized as a drug for alleviating and assisting the treatment of PD.