Cyclocarya paliurus polysaccharides alleviate type 2 diabetic symptoms by modulating gut microbiota and short-chain fatty acids.

BACKGROUND: Cyclocarya paliurus polysaccharide (CCPP), a primary active component in the leaves of Cyclocarya paliurus (Batal.) Iljinsk (C. paliurus), has the ability to treat type 2 diabetes mellitus (T2DM), but cannot be digested by our digestive system. Therefore, mechanisms of regulating the gut microbiota and intestinal metabolites might exist. PURPOSE: To reveal the potential mechanism of CCPP treatment, this study aimed to investigate the alterations of the gut microbiota and intestinal metabolites especially short chain fatty acids (SCFAs) in type 2 diabetic rats. STUDY DESIGN AND METHODS: Type 2 diabetic rat models were developed, and the therapeutic effects of CCPP were evaluated. Metagenomics analysis was utilized to analyze the alterations to the gut microbiota, and UHPLC-QTOF/MS-based untargeted metabolomics analysis of colon contents was used to identify the differential intestinal metabolites. GC/MS was used to measure the SCFAs in rat's colon contents and human fecal inoculums. Furthermore, the expression of SCFA receptors including GPR41, GPR43 and GPR109a was verified by qRT-PCR and the concentration of glucagon-like peptide-1(GLP-1) and peptide tyrosinetyrosine (PYY) was measured by Elisa. RESULTS: Inhibition of the blood glucose levels and improvements in glucose tolerance and serum lipid parameters were observed after CCPP treatment. Eleven SCFA-producing species including Ruminococcus_bromii, Anaerotruncus_colihominis, Clostridium_methylpentosum, Roseburia_intestinalis, Roseburia_hominis, Clostridium_asparagiforme, Pseudoflavonifractor_capillosus, Intestinimonas_butyriciproducens, Intestinimonas_sp._GD2, Oscillibacter_valericigenes and Oscillibacter_ruminantium were clearly increased in the CCPP group. Furthermore, our study indicated that CCPP increases the production of SCFAs both in vivo and in vitro, and the gut microbiota are the key factor of this process. The SCFA receptors including GPR41, GPR43 and GPR109a, were significantly stimulated in the CCPP treated rats, which was accompanied by the upregulated expression of GLP-1 and PYY. CONCLUSION: These results demonstrated that CCPP could alleviate type 2 diabetic symptoms by increasing the SCFA-producing bacteria, promoting the production of SCFAs and upregulating SCFA-GLP1/PYY associated sensory mediators.

Variation in ectomycorrhizal fungal communities associated with Oreomunnea mexicana (Juglandaceae) in a Neotropical montane forest.

Neotropical montane forests are often dominated by ectomycorrhizal (EM) tree species, yet the diversity of their EM fungal communities remains poorly explored. In lower montane forests in western Panama, the EM tree species Oreomunnea mexicana (Juglandaceae) forms locally dense populations in forest otherwise characterized by trees that form arbuscular mycorrhizal (AM) associations. The objective of this study was to compare the composition of EM fungal communities associated with Oreomunnea adults, saplings, and seedlings across sites differing in soil fertility and the amount and seasonality of rainfall. Analysis of fungal nrITS DNA (nuclear ribosomal internal transcribed spacers) revealed 115 EM fungi taxa from 234 EM root tips collected from adults, saplings, and seedlings in four sites. EM fungal communities were equally species-rich and diverse across Oreomunnea developmental stages and sites, regardless of soil conditions or rainfall patterns. However, ordination analysis revealed high compositional turnover between low and high fertility/rainfall sites located ca. 6 km apart. The EM fungal community was dominated by Russula (ca. 36 taxa). Cortinarius, represented by 14 species and previously reported to extract nitrogen from organic sources under low nitrogen availability, was found only in low fertility/high rainfall sites. Phylogenetic diversity analyses of Russula revealed greater evolutionary distance among taxa found on sites with contrasting fertility and rainfall than was expected by chance, suggesting that environmental differences among sites may be important in structuring EM fungal communities. More research is needed to evaluate whether EM fungal taxa associated with Oreomunnea form mycorrhizal networks that might account for local dominance of this tree species in otherwise diverse forest communities.

Soil-borne pathogens restrict the recruitment of a subtropical tree: a distance-dependent effect.

The Janzen-Connell hypothesis suggests that density- and/or distance-dependent juvenile mortality driven by host-specific natural enemies can explain high species diversity in tropical forests. However, such density and distance effects may not occur simultaneously and may not be driven by the same mechanism. Also, reports of attempts to identify and quantify the differences between these processes in tropical forests are scarce. In a primary subtropical forest in China, we (1) experimentally examined the relative influence of the distance to parent trees vs. conspecific seedling density on mortality patterns in Engelhardia fenzelii, (2) tested the role of soil-borne pathogens in driving density- or distance-dependent processes that cause seedling mortality, and (3) inspected the susceptibilities of different tree species to soil biota of E. fenzelii and the effects of soil biota from different tree species on E. fenzelii. The results from these field experiments showed that distance- rather than density-dependent processes driven by soil pathogens strongly affect the seedling survival of this species in its first year. We also observed increased survival of a fungicide treatment for E. fenzelii seedlings in the parent soil but not for the seedlings of the other three species in the E. fenzelii parent soil, or for E. fenzelii seedlings in the parent soil of three other species. This study illustrates how the distance-dependent pattern of seedling recruitment for this species is driven by soil pathogens, a mechanism that likely restricts the dominance of this abundant species.