Cai Song, M.D., Ph.D.
Director and professor of Research Institute for Marine Drugs and Nutrition, Guangdong Ocean University
Background. Clinical and experimental studies have found that increased proinflammatory cytokines in the blood and the cerebrospinal fluid of schizophrenia patients. By contrast, the expression of autophagy function is decreased. The mRNA level of a crucial autophagy-related protein, Beclin 1 was reported to be decreased in the hippocampus of schizophrenia patients. Over-expression of pro-inflammatory cytokines may inhibit autophagy. Autophagy regulates inflammation through innate immune signalling pathways, which removes endogenous inflammasome agonists and negatively regulates secretion of pro-inflammation. Conversely, downregulated autophagy leads to excessive interleukin (IL-1β) secretion, which in turn stimulates autocrine secretion of other pro-inflammatory cytokines and the inflammatory response. The kinase mammalian target of rapamycin (mTOR) is a major regulator of the autophagic process in which the phosphatidylinositol 3-kinase (PI3K/AKT) pathway is upstream of mTOR and modulates its activity. Both mTOR and PI3K/AKT expression are up-regulated in schizophrenia. However, the inter-relationship between chronic inflammation and autophagy, and whether inflammation suppresses autophagy via PI3K/AKT/mTOR signaling pathway, remains unknown in schizophrenia. The aim of current study is to answer these two questions.
Method Proinflammatory cytokines in the plasma of schizophrenia were measured by ELISA. Ultrastructural changes of the peripheral blood mononuclear cells (PBMCs) were examined by transmission electron microscopy. The components of autophagy vesicles, monodasylcadaverine (MDC) autophagy specific fluorescence staining, were measured by flow cytometry. The mRNA and protein expression of PI3K, Akt, mTOR, p70 ribosomal protein S6 kinase(p70S6k), 4EBP1 and Beclin1, and microtubule associated protein 1 light chain 3(LC3)-B/ LC3-A were assayed by real-time fluorescence quantitative RT-PCR and Western blotting respectively.
Result In the blood of schizophrenia patients, mRNA and protein expression of Beclin1 and LC3-B/ LC3-A were significantly decreased while p62 was significantly increased. Expression of mRNA for PI3K, Akt, mTOR, p70S6k and 4EBP1was significantly increased. In parallel, protein expression of PI3K, p-Akt (Ser473), p-mTOR (Ser2448), p-p70S6k (Thr389), and p-4E-BP1 (Thr37/46) was also significantly increased. Furthermore, the concentration of proinflammatory cytokines, such as IL-1β and interferon (IFN-γ) were significantly increased in the plasma of schizophrenia patients.
Conclusion Elevation of IFN-γ and IL-1β levels indicates an increasing inflammatory response in the patients. While the decrease in mRNA and protein expression of beclin1 and LC3-B/ LC3-A mRNA, but increased P62 in the PBMCs of schizophrenia, patients suggests that the function of autophagy was damaged. Furthermore, the results demonstrated that the class I PI3K pathway was activated, followed by the activation of Akt and mTOR, which resulted in the phosphorylation of p70S6K and 4EBP1. These results suggest that activation of the PI3K-Akt-mTOR signaling pathway may inhibit autophagy in schizophrenia. To further reveal the inter-relationship between inflammation and autophagy activity, we plan to incubate rapamycin (autophagy activator) and 3-methyxanthine (autophagy blocker) with PBMCs of schizophrenia patients to define the inflammatory response. This will be followed by incubation of proinflammatory (IL-6) and anti-inflammatory (IL-10) cytokines with PBMCs of schizophrenia patients to investigate autophagy activity.
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