Prox1 heterozygous mice have a defective lymphatic vasculature and develop late-onset obesity. Chyle abnormally leaks from those vessels, accumulates in the surrounding tissues, and causes an increase in adipose tissue. We characterized the lymphatics of Prox1+/– mice to determine whether the extent of obesity correlated with the severity of lymphatic defects. The lymphatic vasculature in Prox1+/– mice exhibited reduced tracer clearance from the ear skin, dysfunctional perfusion of the lower legs, and reduced tracer uptake into the deep lymphatic collectors during mechanostimulation prior to the onset of obesity. Ear lymphatic vessels and leg collectors in Prox1+/– mice were disorganized and irregular, further confirming that defective lymphatic vessels are associated with obesity in Prox1+/– mice. We now provide conclusive in vivo evidence that demonstrates that leaky lymphatics mediate obesity in Prox1+/– mice, as restoration of lymphatic vasculature function was sufficient to rescue the obesity features in Prox1+/– mice. Finally, depth-lipomic profiling of lymph contents showed that free fatty acids induce adipogenesis in vitro.
Authors
Noelia Escobedo, Steven T. Proulx, Sinem Karaman, Miriam E. Dillard, Nicole Johnson, Michael Detmar, Guillermo Oliver
(A) Average body weight of littermate mice measured every week, starting at weaning age. Progressive weight gain was observed in Prox1+/– mice (red dots), but no significant weight gain, compared to that of WT mice (black dots), was observed in Lyve1+/GFPCre;Jojo-Prox1;Prox1+/– (blue dots) littermates. Data are plotted as means ± SEM from male and female mice of at least 7 mice per genotype. (B and C) Leptin (B) and insulin (C) levels were higher in adult Prox1 mice than WT counterparts; however, in Lyve1+/GFPCre;Jojo-Prox1;Prox1+/– mice, the levels were comparable to their WT littermates. (D–M) Rescue of ear lymph flow. Representative photographs of ears at 0 and 24 hours after injection of Evans blue dye into 7-week-old female WT (D–F), Prox1+/– (G–I), and Lyve1+/GFPCre;Jojo-Prox1;Prox1+/– (J–L) mice. (M) Extravasation of Evans blue dye was measured via absorbance at 620 nm. Quantification of the total dye remaining in the ear skin for each genotype shows that the lymph flow defect seen in Prox1+/– mice was improved in Lyve1+/GFPCre;Jojo-Prox1;Prox1+/– mice to the same extent seen in WT siblings. Results are representative of 3 independent experiments. WT, Lyve1+/GFPCre, or Jojo-Prox1 mice were used as WT control mice. Plot shows mean ± SEM. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001, 1-way ANOVA followed by Bonferroni’s multiple comparison test.