Promoting neurogenesis is a promising strategy for the treatment of cognition impairment associated with Alzheimer’s disease (AD). Ganoderma lucidum is a revered medicinal mushroom for health-promoting benefits in the Orient. Here, we found that oral administration of the polysaccharides and water extract from G. lucidum promoted neural progenitor cell (NPC) proliferation to enhance neurogenesis and alleviated cognitive deficits in transgenic AD mice. G. lucidum polysaccharides (GLP) also promoted self-renewal of NPC in cell culture. Further mechanistic study revealed that GLP potentiated activation of fibroblast growth factor receptor 1 (FGFR1) and downstream extracellular signal-regulated kinase (ERK) and AKT cascades. Consistently, inhibition of FGFR1 effectively blocked the GLP-promoted NPC proliferation and activation of the downstream cascades. Our findings suggest that GLP could serve as a regenerative therapeutic agent for the treatment of cognitive decline associated with neurodegenerative diseases.
NPC proliferation, differentiation, and survival of newborn neurons are critical stages in neurogenesis. We observed that GLP treatment did not alter the proportion of neuronal progeny in APP/PS1 mice. Therefore, it is likely that GLP treatment enhanced NPC proliferation to promote neurogenesis. To test this hypothesis, we monitored the expression of a proliferation marker Ki67 in SOX2-positive NPC. Compared with the vehicle-treated APP/PS1 mice, the number of Ki67 and SOX2 double-positive proliferating NPC was increased in the GLP-treated mice . However, the number of SOX2-positive cells was not changed, indicating GLP did not affect NPC pool in APP/PS1 mice . To further investigate whether GLP also promote NPC proliferation in normal mice, we treated 8-week-old C57BL/6 mice with GLP or vehicle for 14 days and mitotic cells were labeled by three BrdU injections on the last day. Histological analysis revealed that there were more BrdU and SOX2 double-positive proliferating NPC in the subgranular zone (SGZ) of GLP-treated mice than in vehicle-treated mice E–3G). However, the number of SOX2-positive cells in the SGZ was not changed, indicating that the NPC pool was not altered by GLP. These results indicate that GLP treatment has general effects of promoting NPC proliferation in both neurodegenerating and normal brains.
AD is a devastating neurodegenerative disease with no effective treatment as yet. Current US Food and Drug Administration-approved AD drugs such as acetylcholinesterase inhibitors and NMDA receptor antagonists only alleviate disease symptoms in about half of the patients for approximately 6–12 months (Winslow et al., 2011). Recent advances in regenerative medicine, which includes stem cell-based therapy and modulation of endogenous neurogenesis, offer a novel therapeutic avenue (Lie et al., 2004). While both of the strategies proved to be feasible and effective in AD animal models, augmenting endogenous neurogenesis by pharmaceutical approaches seems to be more acceptable for patients because of its easy delivery (Miller and Kaplan, 2012). Here, we demonstrate that GLP and WGL ameliorated cognitive dysfunction and promoted NPC proliferation in transgenic AD model mice. Moreover, in an AD Drosophila model, WGL extended the life span and promoted locomotor function, indicating that the benefits of WGL on AD are conservative across model animals of different species. Our results indicate that GLP and WGL have beneficial potential as both preventives and therapeutics for neurodegenerative diseases.
G. lucidum is a medicinal mushroom well known for its legendary anti-aging benefits. Our findings that GLP not only promote NPC proliferation but also reduce amyloid deposits provide potential underlying mechanisms of its anti-aging effects. Extract of G. lucidum has also been reported to inhibit the lipopolysaccharide-induced inflammatory cytokines by activated microglia and thus to protect dopaminergic neurons (Ding et al., 2010). Moreover, WGL attenuates Aβ-induced synaptotoxicity and apoptosis by preserving the synaptic density protein synaptophysin (Lai et al., 2008). These reports, together with our findings, suggest that the multi-target effects of GLP and WGL may have desirable advantages for the treatment of multi-factorial neurodegenerative diseases such as AD.
Despite progress in revealing therapeutic potentials of G. lucidum, the molecular targets of GLP or WGL are still not clear. bFGF and EGF are two critical growth factors that regulate NPC proliferation, survival, and differentiation in the neurogenic region. In this study, we found that GLP activated FGFR1 signaling but not EGFR signaling in a growth-factor-deficient condition. In line with this, inhibition of FGFR1 blocked GLP-promoted NPC proliferation, while inhibition of either downstream ERK or AKT only had moderate blockade effects. Interestingly, GLP had differential effects on FGFR1 activation in the presence or absence of low concentration of bFGF, suggesting that GLP potentiated the response of FGFR1 to bFGF rather than activating FGFR1 by itself. Our results indicate that GLP could potentiate FGFR signaling to promote neurogenesis upon growth factor deficiency, and may serve as a preventive and therapeutic agent against neurodegenerative diseases.
Animals
APP/PS1 transgenic mice were obtained from The Jackson Laboratory (stock no. 004462) and express a chimeric mouse/human amyloid precursor protein containing the K595N/M596L Swedish mutations (APPswe) and a human presenilin 1 with a deletion of exon 9. Heterozygous mice were maintained by crossing with C57BL/6 mice. C57BL/6 mice were obtained from Shanghai Laboratory Animal Center (Chinese Academy of Sciences). The experimental procedures for the use and care of the animals were approved by the Ethics Committees of the Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. All mice were given ad libitum access to food and water.