Light-responsive adipose-hypothalamus axis controls metabolic regulation

Abstract

Light is fundamental for biological life, with most mammals possessing light-sensing photoreceptors in various organs. Opsin3 is highly expressed in adipose tissue which has extensive communication with other organs, particularly with the brain through the sympathetic nervous system (SNS). Our study reveals a new light-triggered crosstalk between adipose tissue and the hypothalamus. Direct blue-light exposure to subcutaneous white fat improves high-fat diet-induced metabolic abnormalities in an Opsin3-dependent manner. Metabolomic analysis shows that blue light increases circulating levels of histidine, which activates histaminergic neurons in the hypothalamus and stimulates brown adipose tissue (BAT) via SNS. Blocking central actions of histidine and denervating peripheral BAT blunts the effects of blue light. Human white adipocytes respond to direct blue light stimulation in a cell-autonomous manner, highlighting the translational relevance of this pathway. Together, these data demonstrate a light-responsive metabolic circuit involving adipose-hypothalamus communication, offering a potential strategy to alleviate obesity-induced metabolic abnormalities.

Fig. 1. Optogenetic blue light to scWAT counteracts high-fat diet-induced metabolic abnormalities.

a–l Studies in 12-15-week-old C57BL/6 J male mice. a Schematic showing µLED device implantation in mouse scWAT (NO, RED, and BLUE light groups). b % BW change over 8 days (NO: n = 10, RED: n = 8, BLUE: n = 7). c Average food intake (NO: n = 7, RED: n = 4, BLUE: n = 4). d Tissue weight relative to BW (NO: n = 10, RED: n = 6, BLUE: n = 7). e Treated and untreated scWAT weight relative to BW (NO: n = 10, RED: n = 6, BLUE: n = 7). f Change in energy expenditure (ΔHeat) after norepinephrine (NE) injection (NO: n = 8, RED: n = 6, BLUE: n = 5). *P < 0.05, vs NO light group. g AUC quantification of ΔHeat (NO: n = 8, RED: n = 6, BLUE: n = 5). h Glucose levels during intraperitoneal glucose tolerance test (IPGTT) (NO, RED, BLUE: n = 6). *P < 0.05, vs NO light group, ^#P < 0.05, vs RED light group. (i) AUC of IPGTT (NO, RED, BLUE: n = 6). j–l Fasting plasma insulin (j) (NO: n = 8, RED: n = 6, BLUE: n = 5), HOMA-IR (k) (NO: n = 7, RED: n = 5, BLUE: n = 5), and plasma leptin levels (l) (NO: n = 9, RED: n = 7, BLUE: n = 6). m–u Studies in 20-25-week-old C57BL/6 J male DIO mice. (m) % BW change over 8 days (NO: n = 6, RED: n = 5, BLUE: n = 6). (n) Average food intake (NO, RED, BLUE: n = 5). o % changes in fat and lean mass over 8 days (DEXA scan) (NO: n = 6, RED: n = 5, BLUE: n = 6). p Treated and untreated scWAT weight relative to BW (NO: n = 6, RED: n = 5, BLUE: n = 5). (q) ΔHeat after NE injection (NO: n = 5, RED: n = 4, BLUE: n = 5). *P < 0.05 vs NO light group. r AUC quantification of ΔHeat (NO: n = 5, RED: n = 4, BLUE: n = 5). s Glucose levels during IPGTT (NO, RED, BLUE: n = 5). t AUC of IPGTT (NO, RED, BLUE: n = 5). u Fasting plasma insulin level (NO: n = 4, RED: n = 4, BLUE: n = 5). Statistics were performed by two-tailed paired Student’s t-tests (e and p), one-way ANOVA followed by Tukey’s post hoc test (b–d, g, i–o, r, t, and u), and two-way ANOVA followed by Tukey’s post hoc test (f, h, q, and s). n.s. indicates no significant difference. Data are represented as mean ± SEM. The diagram in a was created with BioRender.com, released under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International license.

Fig. 2. Direct blue light reduces lipid synthesis but does not induce beiging in scWAT.

a H&E staining of treated scWAT in 12-15-week-old C57BL/6 J male mice exposed to different light wavelengths (no light, red light, and blue light) for 8 days. Scale bars, 50 µm. b and c Adipocytes’ size distribution (b) and the average of adipocytes’ diameter (c) of treated scWAT after 8 days of light exposure (n = 4 per group). d Triglyceride levels in treated scWAT exposed to different light wavelengths. (NO light: n = 6, RED light: n = 5, and BLUE light: n = 5). e and f Relative mRNA expression of indicated lipid/glucose metabolism genes (e) and beiging genes (f) in treated scWAT in mice exposed to different light wavelengths. (NO light: n = 13, RED light: n = 8, and BLUE light: n = 10). g A schematic panel depicting the experimental design for mRNA (qPCR) and glycerol measurement conducted in in vitro differentiated murine white adipocytes (3T3-L1 cells) stimulated with/without blue light exposure. h Relative mRNA expression of lipid/glucose metabolism genes in murine white adipocytes exposed to blue light for a prolonged period (8 days) (h) or for a short-term (1 or 4 hours) (i) relative to dark condition (n = 4 technical replicates per group, three biologically independent replicates per experiment). j Glycerol levels in the culture medium of murine white adipocytes exposed to a short-term blue light exposure (1 or 4 hours) relative to dark condition (n = 4 technical replicates per group, three biologically independent replicates per experiment). Statistics were performed by two-tailed unpaired Student’s t-tests (h–j) and one-way ANOVA followed by Tukey’s post hoc test (c–f). n.s. indicates no significant difference. Data are represented as mean ± SEM. The diagram in g was created with BioRender.com, released under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International license.

Fig. 3. Direct blue light to scWAT triggers activation of endogenous BAT via SNS.

a H&E staining of BAT in 12-15-week-old C57BL/6 J male mice exposed to scWAT by different light wavelengths (no light, red light, and blue light) for 8 days. Scale bars, 50 µm. b–d Triglyceride levels (b) (NO light: n = 7, RED light: n = 8, and BLUE light: n = 4), and relative mRNA expression of indicated lipid/glucose metabolism genes (c) and thermogenesis genes (d) in BAT (NO light: n = 6, RED light: n = 6, and BLUE light: n = 6) in mice exposed to scWAT by different light wavelengths. (e and f) NE levels in BAT (NO light: n = 7, RED light: n = 7, and BLUE light: n = 6) (e), and circulation (NO light: n = 7, RED light: n = 7, and BLUE light: n = 7) (f). (g and h) Systolic and diastolic blood pressure (g) and pulse rate (h) before and after 8 days of light treatment (NO light: n = 6, and BLUE light: n = 5). Statistics were performed by two-tailed paired Student’s t-tests (g and h) and one-way ANOVA followed by Tukey’s post hoc test (b–f). n.s. indicates no significant difference. Data are represented as mean ± SEM.

Fig. 4. Blue light does not induce metabolic changes in Opn3 male knockout mice.

Studies in 12-15-week-old Opn3-global knockout (GKO) and WT male mice. a Schematic showing blue µLED device implantation in mouse scWAT (NO light and BLUE light groups). b % BW change over 8 days (NO light in WT: n = 6, BLUE light in WT: n = 5, NO light in Opn3-GKO: n = 5, and BLUE light in Opn3-GKO: n = 5). c Average food intake (NO light in WT: n = 6, BLUE light in WT: n = 5, NO light in Opn3-GKO: n = 5, and BLUE light in Opn3-GKO: n = 5). d Treated and untreated scWAT weight relative to BW (NO light in WT: n = 6, BLUE light in WT: n = 5, NO light in Opn3-GKO: n = 5, and BLUE light in Opn3-GKO: n = 5). e Glucose levels during intraperitoneal glucose tolerance test (IPGTT) (NO light in WT: n = 3, BLUE light in WT: n = 3, NO light in Opn3-GKO: n = 5, and BLUE light in Opn3-GKO: n = 5). f AUC of IPGTT (NO light in WT: n = 3, BLUE light in WT: n = 3, NO light in Opn3-GKO: n = 5, and BLUE light in Opn3-GKO: n = 5). g Relative mRNA expression of lipid/glucose metabolism genes (NO light in WT: n = 3, BLUE light in WT: n = 3, NO light in Opn3-GKO: n = 5, and BLUE light in Opn3-GKO: n = 5) in treated scWAT of Opn3-GKO and WT mice. Statistics were performed by two-tailed paired Student’s t-tests (d), one-way ANOVA followed by Tukey’s post hoc test (b, c, f, and g), and two-way ANOVA followed by Tukey’s post hoc test (e). n.s. indicates no significant difference. Data are represented as mean ± SEM. The diagram in a was created with BioRender.com, released under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International license.

Fig. 5. Changes in circulating metabolite profiles induced by blue light exposure to scWAT.

a–d Principal components analysis (PCA) plot (a), metabolite set enrichment analysis (MSEA) of altered pathways in circulation in blue lighted groups compared with non-lightened group (b) or red lightened group (c), and variable importance in projection (VIP) (d) from metabolomics analysis of plasma from 12-15-week-old C57BL/6 J male mice exposed to scWAT by different light wavelengths for 8 days (NO light: n = 7, RED light: n = 6, and BLUE light: n = 6). The colored boxes on the right (d) indicate the relative concentrations of the corresponding metabolite in each group under study. e The relative abundance of circulating histidine and carnosine within the histidine metabolism pathway, employing metabolomics analysis (NO light: n = 7, RED light: n = 6, and BLUE light: n = 6). (f and g) Circulating histidine levels in C57BL/6 J male mice (NO light: n = 6, RED light: n = 6, and BLUE light: n = 6) (f) and Opn3-GKO male mice (NO light: n = 5, and BLUE light: n = 4) (g) with/without light treatment for 8 days, measured by ELISA. h and i Clustered heatmap from metabolomics analysis (h) and the relative abundance of histidine and carnosine (i) in treated scWAT with 8 days of blue light exposure relative to no light, employing metabolomics analysis (NO light: n = 6, and BLUE light: n = 5). (j) A positive correlation between the relative abundance of circulating histidine and the histidine in treated scWAT (n = 11). k–m Relative mRNA expression of histidine metabolism genes, Hdc and Carns1, in treated scWAT (n = 8 per group) (k), murine white adipocytes (n = 4 per condition, three biological replicates) (l), and human white adipocytes (n = 3 per condition, three biological replicates) (m) exposed to 8 days of blue light relative to dark condition. Statistics were performed by MSEA (b and c), VIP score (d) using MetaboAnalyst, two-tailed unpaired Student’s t-tests (g, i, and k–m), one-way ANOVA followed by Tukey’s post hoc test (e and f), and Spearman’s Rank correlation test (two-tailed) (j). n.s. indicates no significant difference. n.d. indicates no determined. Data are represented as mean ± SEM.

Fig. 6. Blue light-induced histidine increases HDC-responsive neurons in the hypothalamus and activates BAT via sympathetic nervous system.

a Schematic of histidine metabolism pathway showing circulating histidine and FMH (HDC antagonist) mediates histaminergic neurons in the hypothalamus and regulates BAT thermogenesis via sympathetic nervous system (SNS). b Histidine decarboxylase (HDC) activity, normalized to total protein (right panel) or tissue weight (left panel), in the isolated brain tissues containing the hypothalamus in mice treated with/without 8 days of blue light exposure plus PBS or FMH injection. (NO light + PBS: n = 6, BLUE light + PBS: n = 3, and BLUE light + FMH: n = 4). c Immunostaining of histaminergic neurons in the hypothalamus in mice treated with/without 8 days of blue light exposure plus PBS or FMH injection. Sections at 1.7 mm and 2.7 mm posterior to the bregma were stained for mouse HDC (red). DAPI (4′,6-diamidino-2-phenylindole) was used to visualize nuclei (blue). Scale bar: 200 μm (two left columns), 20 μm (three right columns). d Relative tyrosine hydroxylase (Th) mRNA expression in BAT in mice treated with non- or 8 days of blue light exposure to scWAT plus PBS or FMH injection (NO light + PBS: n = 5, BLUE light + PBS: n = 6, and BLUE light + FMH: n = 6). e Th immunostaining (green) in BAT sections from mice treated with/without 8 days blue lighting plus PBS or FMH injection. DAPI (4′,6-diamidino-2-phenylindole) was used to visualize nuclei (blue). Scale bar: 50 μm. f Quantification of percentage Th density in BAT sections (NO light + PBS: n = 5, BLUE light + PBS: n = 5, and BLUE light + FMH: n = 3). Statistics were performed by one-way ANOVA followed by Tukey’s post hoc test. Data are represented as mean ± SEM.

Fig. 7. Blue light-induced metabolic alterations are blunted by histidine decarboxylase antagonist.

a Schematic model showing blue µLED implantation in mouse scWAT with/without light treatment plus PBS or FMH injection. b % BW change over 8-days (NO light + PBS: n = 6, NO light + FMH: n = 8, BLUE light + PBS: n = 5, and BLUE light + FMH: n = 6). c Average food intake (NO light + PBS: n = 4, and NO light + FMH: n = 7). d Tissue weight relative to BW (NO light + PBS: n = 6, NO light + FMH: n = 8, BLUE light + PBS: n = 4, and BLUE light + FMH: n = 6). e Treated and untreated scWAT weight relative to BW (NO light + PBS: n = 6, NO light + FMH: n = 8, BLUE light + PBS: n = 4, and BLUE light + FMH: n = 6). f Change of heat after norepinephrine (NE) injection (NO light + PBS: n = 7, NO light + FMH: n = 10, BLUE light + PBS: n = 7, and BLUE light + FMH: n = 9). *P < 0.05, vs NO light + PBS, ^#P < 0.05, vs NO light + FMH. (g) Relative mRNA expression of indicated thermogenic and lipolytic genes in BAT (NO light + PBS: n = 6, NO light + FMH: n = 7, BLUE light + PBS: n = 7, and BLUE light + FMH: n = 6). h Plasma NE levels (NO light + PBS: n = 6, NO light + FMH: n = 8, BLUE light + PBS: n = 7, and BLUE light + FMH: n = 6). i The relative abundance of circulating histidine and carnosine, employing metabolomics analysis. (BLUE light + PBS: n = 5, and BLUE light + FMH: n = 4). j Proposed model for the underlying mechanism of the light-responsive adipose-hypothalamus axis in metabolic regulation. Statistics were performed by two-tailed paired Student’s t-tests (e), two-tailed unpaired Student’s t-tests (c and i), one-way ANOVA followed by Tukey’s post hoc test (b, d, g and h), and two-way ANOVA followed by Tukey’s post hoc test (f). Data are represented as mean ± SEM. The diagrams in a and j were created with BioRender.com, released under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International license.