Wireless optogenetics protects against obesity via stimulation of non-canonical fat thermogenesis

Abstract

Cold stimuli and the subsequent activation of β-adrenergic receptor (β-AR) potently stimulate adipose tissue thermogenesis and increase whole-body energy expenditure. However, systemic activation of the β3-AR pathway inevitably increases blood pressure, a significant risk factor for cardiovascular disease, and, thus, limits its application for the treatment of obesity. To activate fat thermogenesis under tight spatiotemporal control without external stimuli, here, we report an implantable wireless optogenetic device that bypasses the β-AR pathway and triggers Ca²⁺ cycling selectively in adipocytes. The wireless optogenetics stimulation in the subcutaneous adipose tissue potently activates Ca²⁺ cycling fat thermogenesis and increases whole-body energy expenditure without cold stimuli. Significantly, the light-induced fat thermogenesis was sufficient to protect mice from diet-induced body-weight gain. The present study provides the first proof-of-concept that fat-specific cold mimetics via activating non-canonical thermogenesis protect against obesity.

Fig. 1. Wireless optogenetics implant stimulates Ca²⁺ influx in adipocytes.

a A representative image of a freely behaving mouse with the implantable wireless optogenetics device in the inguinal WAT (arrow heads). Scale bar, 1 mm. b Three-dimensional illustration of the implantable wireless optogenetics device and the circuit diagram. c Schematic of optogenetic studies in cultured cells. d–g Real-time changes in intracellular Ca²⁺ influx following optogenetic light stimulations with indicated pulse width (d) or pulse frequency (f). d Cells stimulated with pulse width at 1 ms, n = 104; at 5 or 10 ms, n = 140. f Cells stimulated with pulse frequency at 1 or 10 Hz, n = 140; at 20 Hz, n = 134. Quantification of intracellular Ca²⁺ influx in ChR2-expressing adipocytes stimulated with indicated pulse width (e) or pulse frequency (g) and the heat emission from the device. The data of heat emission from the device were derived from Supplementary Fig. 1c for (e) or 1d for (g). h Real-time changes in intracellular Ca²⁺ influx following optogenetic light stimulation. Vector control, n = 123; ChR2, n = 128. i Expression of indicated voltage-gated Ca²⁺ channels in isolated beige adipocytes (E-MTAB-3978). n = 3. j Real-time changes (left) and quantification (right) in intracellular Ca²⁺ influx following optogenetic light stimulation. ChR2 with vehicle, n = 128; ChR2 with L-type inhibitor, n = 140; ChR2 with R-type inhibitor, n = 155; ChR2 with T-type inhibitor, n = 134; Vector control with vehicle, n = 139. k Real-time changes (left) and quantification (right) in intracellular Ca²⁺ influx following optogenetic light stimulation. ChR2 with vehicle, n = 105; ChR2 with RyR2 inhibitor, n = 131; ChR2 with IP₃R inhibitor, n = 120; ChR2 with RyR2 inhibitor and IP₃R inhibitor, n = 140; Vector control with vehicle, n = 140. l Quantification of light-stimulated OCR following optogenetics light stimulation. Vector control with vehicle, n = 12; Vector control with L-type inhibitor, n = 15; ChR2 with vehicle, n = 19, ChR2 with L-type inhibitor, n = 15. m Glucose oxidation in differentiated adipocytes expressing ChR2 or vector control with or without optogenetics light stimulation. n = 6. Data were analyzed by one-way ANOVA (j–l) or two-way ANOVA (m) by Tukey’s post hoc test. All Data are expressed as means ± s.e.m. n.s. not significant.

Fig. 2. Wireless optogenetics stimulates Ca²⁺ cycling fat thermogenesis through SERCA2.

a Schematic illustration of the tissue temperature recording in device-implanted mice. b Real-time changes in the inguinal WAT temperature of Adipo-ChR2 mice and littermate controls following optogenetic stimulation. Control, n = 4; Adipo-ChR2, n = 3. c Quantification of light-induced thermogenesis in the inguinal WAT and iBAT of Adipo-ChR2 mice and littermate controls in b. Control, n = 4; Adipo-ChR2, n = 3. d Real-time changes in intracellular Ca²⁺ influx in wild-type, Ucp1 KO, and Serca2KD beige adipocytes following optogenetics light stimulation. Wild-type, n = 134 for both groups; Ucp1 KO control, n = 140; Ucp1 KO-ChR2, n = 139; Serca2KD control, n = 139; Serca2KD-ChR2, n = 134. e Schematic illustration of the experiment. AAV-GFP or AAV-ChR2 were injected into the inguinal WAT of Adipo-Serca2 KO and age-matched control mice. f mRNA expression of ChR2 in the left side (with AAV) and the right side (without AAV) of inguinal WAT. mRNA expression was normalized to 36B4. Control with AAV-GFP, n = 3 for with or without AAV; Control with AAV-ChR2, n = 4 for with or without AAV; Adipo- Serca2 KO with AAV-ChR2, n = 3 for with or without AAV. g Quantification of light-stimulated thermogenesis in the inguinal WAT of mice in f. Control with AAV-GFP, n = 4; Control with AAV-ChR2, n = 5; Adipo- Serca2 KO with AAV-ChR2, n = 5. Data were analyzed by two-way repeated measures ANOVA (b), unpaired two-sided t-test (c, f), or two-way ANOVA (d) or one-way ANOVA (g) by Tukey’s post hoc test. All Data are expressed as means ± s.e.m. n.s. not significant.

Fig. 3. Wireless optogenetics increases whole-body energy expenditure at thermoneutrality.

a Whole-body oxygen consumption rate (VO₂) of Adipo-ChR2 mice and littermate controls following optogenetics light stimulation at thermoneutrality (left). The quantification of light-stimulated VO₂ is shown on the right graph. Control, n = 8; Adipo-ChR2, n = 11. b Whole-body VO₂ following a single administration of β3 adrenergic receptor agonist (CL-316,243 at 0.01 mg kg⁻¹) or vehicle (saline) at thermoneutrality. The quantification of CL-316,243 or saline-induced VO₂ of wild-type mice is shown on the right. saline, n = 7; CL-316,243, n = 7. Data were analyzed by two-way repeated-measures ANOVA followed by post-hoc paired/unpaired t-test with Bonferroni’s correction (left in a–b) or unpaired two-sided t-test (right in a–b). All Data are expressed as means ± s.e.m. n.s. not significant.

Fig. 4. Light-induced adipose tissue thermogenesis prevents diet-induced obesity.

a Changes in body weight of Adipo-ChR2 mice and littermate controls. Control, n = 8; Adipo-ChR2, n = 10. b Food intake of Adipo-ChR2 mice and littermate control mice in a. Control, n = 8; Adipo-ChR2 n = 10. c Body composition of Adipo-ChR2 mice and littermate controls in a. Control, n = 8; Adipo-ChR2, n = 10. d Tissue-weight of adipose tissues and liver of Adipo-ChR2 mice and littermate controls in a. Control, n = 8; Adipo-ChR2, n = 10. e Representative images of hematoxylin and eosin (H&E) staining of the inguinal WAT from Adipo-ChR2 mice (lower panel) and the littermate controls (upper panel). Scale bars,100 μm. f Histogram (left panel) and quantification (right panel) of adipocyte size in the inguinal WAT in e. Control, n = 5; Adipo-ChR2, n = 5. Data were analyzed by two-way repeated-measures ANOVA followed by post hoc unpaired t-test with Bonferroni’s correction (a), unpaired two-sided t-test (b–d, and f). All data are expressed as means ± s.e.m. n.s. not significant.