Fig 2: Schematic diagram of the molecular mechanisms underlying FNDC4-mediated protection against cardiac I/R injury.FNDC4 is elevated during cardiac I/R injury, which blocks the proteasomal degradation of HIF1α and subsequently activates HIF1α signaling pathway to inhibit cardiomyocyte apoptosis. In addition, FNDC4-mediated HIF1α activation increases the expression and secretion of FGF1 from cardiomyocytes to enhance the angiogenic capacity of endothelial cells in a paracrine manner to facilitate cardiac repair during I/R stress.

Fig 3: FNDC4 promotes angiogenesis of endothelial cells through increasing FGF1 secretion from cardiomyocytes.a Human umbilical vein endothelial cells (HUVECs) were cultured with the conditioned medium (NRCMs-ConM) for 24 h, and then EdU+ nuclei were quantified using a commercial kit (n = 6 independent experiments). b HUVECs were cultured with NRCMs-ConM for 24 h, and then exposed to transwell assay. After 12 h, cells in the lower chamber were stained with crystal violet to quantify the migrated cells (n = 6 independent experiments). c HUVECs were cultured with NRCMs-ConM for 24 h, and then exposed to tube formation assay. After 8 h, the branching length and junction number were quantified (n = 6 independent experiments). d The upregulated angiogenic factors in FNDC4-overexpressed hearts were analyzed using the transcriptome data (n = 3). e The mRNA levels of fibroblast growth factor 1 (Fgf1), slit guidance ligand 1 (Slit1) and Slit2 in NRCMs with or without FNDC4 overexpression (n = 6 independent experiments). f The levels of FGF1, SLIT1 and SLIT2 in the medium of NRCMs with or without FNDC4 overexpression (n = 6 independent experiments). g The level of FGF1 in the medium of NRCMs with brefeldin A (BFA) or BAPTA-AM treatment (n = 6 independent experiments). h Single-cell sequencing data of FGF1 in human hearts. i HUVECs were cultured with NRCMs-ConM in the presence of anti-FGF1 or PD173074 for 24 h, and then EdU+ nuclei were quantified using a commercial kit (n = 6 independent experiments). j HUVECs were cultured with NRCMs-ConM in the presence of anti-FGF1 or PD173074 for 24 h, and then exposed to tube formation assay (n = 6 independent experiments). Data were presented as the mean ± S.D., and analyzed using an unpaired two-tailed Student′s t-test. For the analysis in (g–j), one-way ANOVA followed by Tukey post hoc test was used. *P < 0.0001. Source data are provided as a Source Data file.

Fig 4: Significant alterations in several key genes associated with proinflammation and angiogenesis in diabetic skin. Levels of genes that are key regulators for proinflammation and angiogenesis were shown. A IL1β. B TNFα. C IFNɣ. D IL6. E IL10. F CD163. G TGFβ1. H VEGF-A. I FGF1. *p < 0.05. NS non-significant. DFS diabetic foot skin. NDFS non-diabetic foot skin

Fig 5: Loss of METTL3 alters FGF1 levels.(A) Proteomic changes in the heart following 2 weeks of Western diet. (B) Venn diagram showing 247 and 198 proteins were increased and decreased, respectively, by Western diet with log2(fold-change) greater than 1.0 or less than –1.0. n = 3 pooled samples per condition. (C) Overlap between 445 differentially expressed proteins detected by mass spectrometry and 1,633 transcripts identified by Nanopore. (D) Overlap between 60 transcript/protein targets and 873 proteins annotated as secreted on Uniprot. (E and F) Adipokine arrays and quantification of plasma pooled from n = 3 (CD Ctrl and M3KO) or n = 4 (WD Ctrl and M3KO) mice after 2 weeks on diet. (G) FGF1 ELISA on plasma isolated from mice after 2 weeks on diet. n = (3; 3; 10; 9) (CD Ctrl; CD M3KO; WD Ctrl; WD M3KO). (H) qPCR on 3T3-L1 adipocytes following FGF1 or control treatment. Gene expression normalized to Rpl7. (I) Schematic of Fgf1 showing location of m6A methylation upon Western diet in the 3’ UTR. (J) m6A-immunoprecipitation to identify presence of m6A on transcripts, normalized to input. Input and IgG used as controls. n = 4 per group. (K and L) Western blot from H9C2 cardiomyoblasts transfected with small interfering negative control (siNC) or small interfering against METTL3 (siM3). FGF1 expression normalized to Ponceau. n = 4 per group. (M) Fgf1 mRNA decay in H9C2 cells following the transcription inhibitor actinomycin D for the indicated time. n = 5 per group. Data shown as mean ± SEM. Two-way ANOVA with multiple comparisons test (G), unpaired t test (H and L), 1-way ANOVA with multiple comparisons test (J), and nonlinear fit with least squared regression and extra sum-of-squares F test (M) were used. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001.