Retinoic acid is abundantly detected in different depots of adipose tissue by SERS

Figures & data

Figure 1. RA pathway is differentially regulated in stem cells from VS and SC fat depots. A schematic illustrating RA synthesis / metabolism and downstream pathway regulated by RA. RA is produced in 2 sequential steps from retinol to retinal (a.k.a. retinaldehyde) by RDH10 and DHRS3, then to all-trans RA by 3 isoforms of ALDH1. WT1, a developmental marker of mesothelial layer including VS fat, controls expression of ALDH1A2 isoform. CRBP1 transports cellular retinol and retinal. Finally CYP26 family metabolizes RA into hydroxy-RA. RA acts as a major signaling molecule that binds to its receptors, RARs and RXRs. RARs then bind to its response elements (RARE), leading to modulation of various downstream target genes. Genes highlighted in red are those upregulated in VS-ASCs whereas those highlighted in blue upregulated in SC-ASCs.

Figure 2. SERS measurement of RA levels. (A) Reaction scheme for the peroxidase reaction of TMB to TMB²⁺ using HRP conjugate as enzyme. Peroxidase product TMB²⁺ was then mixed with Au colloid for SERS measurement. (B) SERS spectra of the reactant TMB and product TMB²⁺ are shown for comparison. (C) RA concentration dependent SERS spectra of TMB²⁺. RA levels were calculated based on the intensity of 1605 cm⁻¹ peak from TMB²⁺.

Figure 3. Endogenous RA levels in different tissues of mice under NC diet. Different tissues were harvested from 10-week old, male C57Bl/6J mice fed on normal chow (NC) diet (n = 4). Tissues investigated for RA concentrations by SERS were SC-WF (inguinal Subcutaneous White Fat), VS-WF (epididymal Visceral White Fat), BF (Brown Fat from the interscapular region), Eyes, Liver, SkM (quadriceps Skeletal Muscle), Heart, Sple. (Spleen), Kidn. (Kidney), Panc. (Pancreas). This result is a representative of 2 independent experiments. *p < 0.05, **p < 0.01.

Figure 4. Endogenous RA levels in different tissues of mice under HF diet. The same set of tissues as in Figure 3 were harvested from 20-week old, male C57Bl/6J mice fed on high fat (HF) diet for 12 weeks (n = 3). The tissues were then measured for their RA levels by SERS. The result shown is a representative of 2 independent experiments. *p < 0.05, **p < 0.01.