Fig. 4: Deciphering metabolic communication between organs.

a AFADESI-MS images of palmitic acid with a heatmap representing the signal intensity across organs (left) and images of palmitic acid M6 with a heatmap representing the ME across organs (right). Signal intensity is shown in ion counts. Bra, brain; Liv, liver; Kid, kidney; Hea, heart; Spleen, spl; Lun, lung; Pan, pancreas; BAT, brown adipose tissue; Int, intensity. b Schematic illustrating the incorporation of carbon from U-¹³C-glucose into palmitic acid. Light green circles denote ¹³C carbons, while white circles represent ¹²C carbons. CAR, carnitine; CoA, coenzyme A. c AFADESI-MS images of acetylcarnitine M2. Signal intensity is shown in ion counts. d Normalized labeling fraction of acetylcarnitine M2 across organs, as measured by LC‒MS. Data are presented as mean ± SD (n = 3 biological replicates). e Normalized labeling fraction of palmitoylcarnitine isotopologues in the BAT and brain. Data are presented as mean ± SD (n = 3 biological replicates). f Normalized labeling fraction of hexanoylcarnitine M2 in BAT, brain, heart and serum. Data are presented as mean ± SD (n = 3 biological replicates). g Labeling profile of palmitic acid in BAT, brain and serum. Data are presented as mean ± SD (n = 3 biological replicates). Source data are provided as a Source Data file. h Representative lipid profiles of TG (48:1) in BAT, brain, liver and serum. The color in the heatmap represents labeled fraction (LF) after logarithmic transformation. i Distinct labeling profile of representative lipids between the brain and liver. Lipids in the brain can incorporate more ¹³C carbons (up to M7), whereas lipids in the liver can only be labeled with M3, as measured by LC‒MS. j The potential ¹³C-carbon allocation of labeled TG (48:1). k Illustration of the proposed metabolic crosstalk model, created in BioRender. Li, X. (https://BioRender.com/plw7j67).