Effects of housing conditions on behaviors and biochemical parameters in juvenile cynomolgus monkeys (Macaca fascicularis)

Improving transparency-A call to include social housing information in biomedical research articles involving nonhuman primates

The social setting of animal subjects in the research environment has known effects on a variety of dependent measures used in biomedical research. Proper evaluation of the robustness of published research is dependent upon transparent, detailed, and accurate reporting of research methods, including the animals' social housing conditions. However, to date, most research articles utilizing nonhuman primates (NHPs) provide only partial data on this topic, hampering transparency, and reproducibility. Therefore, we call for the inclusion of information pertaining to the social aspects of the animals' housing conditions in publications involving NHPs to improve transparency. We argue that including this information in scientific publications is crucial for the interpretation of research findings in the appropriate context and for understanding unexplained variability in study findings. Finally, the inclusion of this information in publications will additionally familiarize scientists with how other researchers conducting similar studies are housing their animals and will encourage them to consider the implications of various housing conditions on their research outcomes.

A gut-derived metabolite alters brain activity and anxiety behaviour in mice

Integration of sensory and molecular inputs from the environment shapes animal behaviour. A major site of exposure to environmental molecules is the gastrointestinal tract, in which dietary components are chemically transformed by the microbiota1 and gut-derived metabolites are disseminated to all organs, including the brain2. In mice, the gut microbiota impacts behaviour3, modulates neurotransmitter production in the gut and brain4,5, and influences brain development and myelination patterns6,7. The mechanisms that mediate the gut-brain interactions remain poorly defined, although they broadly involve humoral or neuronal connections. We previously reported that the levels of the microbial metabolite 4-ethylphenyl sulfate (4EPS) were increased in a mouse model of atypical neurodevelopment8. Here we identified biosynthetic genes from the gut microbiome that mediate the conversion of dietary tyrosine to 4-ethylphenol (4EP), and bioengineered gut bacteria to selectively produce 4EPS in mice. 4EPS entered the brain and was associated with changes in region-specific activity and functional connectivity. Gene expression signatures revealed altered oligodendrocyte function in the brain, and 4EPS impaired oligodendrocyte maturation in mice and decreased oligodendrocyte-neuron interactions in ex vivo brain cultures. Mice colonized with 4EP-producing bacteria exhibited reduced myelination of neuronal axons. Altered myelination dynamics in the brain have been associated with behavioural outcomes7,9-14. Accordingly, we observed that mice exposed to 4EPS displayed anxiety-like behaviours, and pharmacological treatments that promote oligodendrocyte differentiation prevented the behavioural effects of 4EPS. These findings reveal that a gut-derived molecule influences complex behaviours in mice through effects on oligodendrocyte function and myelin patterning in the brain.

Environmental Complexity and Research Outcomes

Environmental complexity is an experimental paradigm as well as a potential part of animals' everyday housing experiences. In experimental uses, researchers add complexity to stimulate brain development, delay degenerative brain changes, elicit more naturalistic behaviors, and test learning and memory. Complexity can exacerbate or mitigate behavioral problems, give animals a sense of control, and allow for expression of highly driven, species-typical behaviors that can improve animal welfare. Complex environments should be designed thoughtfully with the animal's natural behaviors in mind, reported faithfully in the literature, and evaluated carefully for unexpected effects.

Paracrine-endocrine FGF chimeras as potent therapeutics for metabolic diseases

Background

The development of a clinically useful fibroblast growth factor 21 (FGF21) hormone has been impeded by its inherent instability and weak FGF receptor (FGFR) binding affinity. There is an urgent need for innovative approaches to overcome these limitations.

Methods

We devised a structure-based chimerisation strategy in which we substituted the thermally labile and low receptor affinity core of FGF21 with an HS binding deficient endocrinised core derived from a stable and high receptor affinity paracrine FGF1 (FGF1^ΔHBS). The thermal stability, receptor binding ability, heparan sulfate and βKlotho coreceptor dependency of the chimera were measured using a thermal shift assay, SPR, SEC-MALS and cell-based studies. The half-life, tissue distribution, glucose lowering activity and adipose tissue remodeling were analyzed in normal and diabetic mice and monkeys.

Findings

The melting temperature of the engineered chimera (FGF1^ΔHBS-FGF21^C-tail) increased by ∼22 °C relative to wild-type FGF21 (FGF21^WT), and resulted in a ∼5-fold increase in half-life in vivo. The chimera also acquired an ability to bind the FGFR1c isoform – the principal receptor that mediates the metabolic actions of FGF21 – and consequently was dramatically more effective than FGF21^WT in correcting hyperglycemia and in ameliorating insulin resistance in db/db mice. Our chimeric FGF21 also exerted a significant beneficial effect on glycemic control in spontaneous diabetic cynomolgus monkeys.

Interpretation

Our study describes a structure-based chimerisation approach that effectively mitigates both the intrinsically weak receptor binding affinities and short half-lives of endocrine FGFs, and advance the development of the FGF21 hormone into a potentially useful drug for Type 2 diabetes.