Behavior, Neural Structure, and Metabolism in Adult Male Mice Exposed to Environmentally Relevant Doses of Di(2-ethylhexyl) Phthalate Alone or in a Phthalate Mixture.

BACKGROUND: We have previously shown that chronic exposure of adult male mice to low doses of di(2-ethylhexyl) phthalate (DEHP) altered male sexual behavior and induced down-regulation of the androgen receptor (AR) in the neural circuitry controlling this behavior. OBJECTIVES: The cellular mechanisms induced by chronic exposure of adult male mice to low doses of DEHP alone or in an environmental phthalate mixture were studied. METHODS: Two-month-old C57BL/6J males were exposed orally for 8 wk to DEHP alone (0, 5, or 50µg/kg/d) or to DEHP (50µg/kg/d) in a phthalate mixture. Behavior, dendritic density per 50-µm length, pre-/postsynaptic markers, synapse ultrastructure, and bioenergetic activity were analyzed. RESULTS: Mice exposed to DEHP either alone or in a phthalate mixture differed in mating, emission of ultrasonic vocalizations, and the ability to attract receptive females in urinary preference tests from control mice. Analyses in the medial preoptic area, the key hypothalamic region involved in male sexual behavior, showed lower dendritic spine density and protein levels of glutamate receptors and differences in other postsynaptic components and presynaptic markers between the treated groups. Ultrastructural observation of dendritic synapses by electron microscopy showed comparable morphology between the treated groups. Metabolic analyses highlighted differences in hypothalamic metabolites of males exposed to DEHP alone or in a phthalate mixture compared to control mice. These differences included lower tryptophan and higher NAD+ levels, respectively, a precursor and end product of the kynurenine pathway of tryptophan metabolism. The protein amounts of the xenobiotic aryl hydrocarbon receptor, one of the targets of this metabolic pathway and known negative regulator of the AR, were higher in the medial preoptic area of exposed male mice. DISCUSSION: Differences in behavior of male mice exposed to environmental doses of phthalates were associated with differences in neural structure and metabolism, with possibly a key role of the kynurenine pathway of tryptophan metabolism in the effects mediated by these substances. https://doi.org/10.1289/EHP11514.

Cognitive and hippocampal effects of adult male mice exposure to environmentally relevant doses of phthalates.

We recently showed that chronic exposure of adult male mice to environmental doses of DEHP alone or in a phthalate mixture altered blood brain barrier integrity and induced an inflammatory profile in the hippocampus. Here, we investigate whether such exposure alters hippocampus-dependent behavior and underlying cellular mechanisms. Adult C57BL/6 J male mice were continuously exposed orally to the vehicle or DEHP alone (5 or 50 µg/kg/d) or to DEHP (5 µg/kg/d) in a phthalate mixture. In the Morris water maze, males showed reduced latencies across days to find the platform in the cue and spatial reference memory tasks, regardless of their treatment group. In the probe test, DEHP-50 exposed males displayed a higher latency to find the platform quadrant. In the temporal order memory test, males exposed to DEHP alone or in a phthalate mixture were unable to discriminate between the most recently and previously seen objects. They also displayed reduced ability to show a preference for the new object in the novel object recognition test. These behavioral alterations were associated with a lowered dendritic spine density and protein levels of glutamate receptors and postsynaptic markers, and increased protein levels of the presynaptic synaptophysin in the hippocampus. Metabolomic analysis of the hippocampus indicated changes in amino acid levels including reduced tryptophan and L-kynurenine and elevated NAD + levels, respectively, a precursor, intermediate and endproduct of the kynurenine pathway of tryptophan metabolism. Interestingly, the protein amounts of the xenobiotic aryl hydrocarbon receptor, a target of this metabolic pathway, were elevated in the CA1 area. These data indicate that chronic exposure of adult male mice to environmental doses of DEHP alone or in a phthalate mixture impacted hippocampal function and structure, associated with modifications in amino acid metabolites with a potential involvement of the kynurenine pathway of tryptophan metabolism.

The primary cilium and lipophagy translate mechanical forces to direct metabolic adaptation of kidney epithelial cells.

Organs and cells must adapt to shear stress induced by biological fluids, but how fluid flow contributes to the execution of specific cell programs is poorly understood. Here we show that shear stress favours mitochondrial biogenesis and metabolic reprogramming to ensure energy production and cellular adaptation in kidney epithelial cells. Shear stress stimulates lipophagy, contributing to the production of fatty acids that provide mitochondrial substrates to generate ATP through ß-oxidation. This flow-induced process is dependent on the primary cilia located on the apical side of epithelial cells. The interplay between fluid flow and lipid metabolism was confirmed in vivo using a unilateral ureteral obstruction mouse model. Finally, primary cilium-dependent lipophagy and mitochondrial biogenesis are required to support energy-consuming cellular processes such as glucose reabsorption, gluconeogenesis and cytoskeletal remodelling. Our findings demonstrate how primary cilia and autophagy are involved in the translation of mechanical forces into metabolic adaptation.

Fluid flow-induced shear stress controls the metabolism of proximal tubule kidney epithelial cells through primary cilium-dependent lipophagy and mitochondria biogenesis.

The kidney, similar to many other organs, has to face shear stress induced by biological fluids. How epithelial kidney cells respond to shear stress is poorly understood. Recently we showed in vitro and in vivo that proximal tubule epithelial cells use lipophagy to fuel mitochondria with fatty acids. Lipophagy is stimulated by a primary cilium-dependent signaling that converges at AMP kinase. AMP kinase is a central signaling hub to trigger lipophagy and also to stimulate mitochondrial biogenesis. These two pathways contribute to generate ATP needed to support energy-consuming cellular processes such as glucose reabsorption, gluconeogenesis. These findings demonstrate the role of the primary cilium and selective macroautophagy/autophagy to integrate shear stress and to sustain the execution of a specific cellular program.