An amazing article by Cao et al. brings home the intimate attachment between mental well-being and health - in mice (and by implication, for us too). An enriched environment promotes formation of a nerve growth factor which in turn inhibits tumor growth through a series of biochemical steps, shown in the summary graphic before the abstract. A commentary by Jonah Lehrer notes that we need "a new metaphor for the interactions of the brain and body. They aren't simply connected via some pipes and tubes. They are emulsified together, so hopelessly intertwined that everything that happens in one affects the other. Holism is the rule."
Cancer is influenced by its microenvironment, yet broader, environmental effects also play a role but remain poorly defined. We report here that mice living in an enriched housing environment show reduced tumor growth and increased remission. We found this effect in melanoma and colon cancer models, and that it was not caused by physical activity alone. Serum from animals held in an enriched environment (EE) inhibited cancer proliferation in vitro and was markedly lower in leptin. Hypothalamic brain-derived neurotrophic factor (BDNF) was selectively upregulated by EE, and its genetic overexpression reduced tumor burden, whereas BDNF knockdown blocked the effect of EE. Mechanistically, we show that hypothalamic BDNF downregulated leptin production in adipocytes via sympathoneural β-adrenergic signaling. These results suggest that genetic or environmental activation of this BDNF/leptin axis may have therapeutic significance for cancer.