Hypothalamic endocannabinoids inversely correlate with the development of diet-induced obesity in male and female mice

Abstract

The endocannabinoid (eCB) system regulates energy homeostasis and is linked to obesity development. However, the exact dynamic and regulation of eCBs in the hypothalamus during obesity progression remain incompletely described and understood. Our study examined the time course of responses in two hypothalamic eCBs, 2-arachidonoylglycerol (2-AG) and arachidonoylethanolamine (AEA), in male and female mice during diet-induced obesity and explored the association of eCB levels with changes in brown adipose tissue (BAT) thermogenesis and body weight. We fed mice a high-fat diet (HFD), which induced a transient increase (substantial at 7 days) in hypothalamic eCBs, followed by a progressive decrease to basal levels with a long-term HFD. This transient rise at early stages of obesity is considered a physiologic compensatory response to BAT thermogenesis, which is activated by diet surplus. The eCB dynamic was sexually dimorphic: hypothalamic eCBs levels were higher in female mice, who became obese at later time points than males. The hypothalamic eCBs time course positively correlated with thermogenesis activation, but negatively matched body weight, leptinemia, and circulating eCB levels. Increased expression of eCB-synthetizing enzymes accompanied the transient hypothalamic eCB elevation. Icv injection of eCB did not promote BAT thermogenesis; however, administration of thermogenic molecules, such as central leptin or a peripheral β3-adrenoreceptor agonist, induced a significant increase in hypothalamic eCBs, suggesting a directional link from BAT thermogenesis to hypothalamic eCBs. This study contributes to the understanding of hypothalamic regulation of obesity.

mTORC1 and CB1 receptor signaling regulate excitatory glutamatergic inputs onto the hypothalamic paraventricular nucleus in response to energy availability

“…In particular, while changes in mEPSC frequency could still be observed after 1 week of HFD in response to mTOR and CB1R blockade (Figure 4C), this was not anymore the case after 4 weeks of HFD (Figure 4E), implying that effects might have been occluded by changes in mTOR and CB1R activity induced by the HFD. Supporting this interpretation, hypothalamic endocannabinoid levels are very high in mice after 1 week of HFD, returning slowly to basal, chow-like levels, after 8 weeks on the diet [53]. Remarkably, we observed that ability of AM251 to increase mEPSC at parvocellular neurons was particularly evident at 1 week of HFD (Figure 4G) and that, for the same time point, inhibitory action of WIN on mEPSC was blunted (Figure 4H).…”

“…Both hypothalamic mTORC1 and CB1R signaling are known to be altered by HFD feeding [50], [51], [52], [53]. Hence, we wondered if HFD exposure could modify mEPSC frequency and how, in turn, modulation of mEPSC frequency by mTORC1 and CB1R signaling could be altered by obesogenic conditions.…”

Carnitine palmitoyltransferase 1C negatively regulates the endocannabinoid hydrolase ABHD6 in mice, depending on nutritional status

“…Next, 50 μl of the homogenized sample were kept at −20 C for protein quantification, and the remaining 150 μl were mixed with 600 μl ethyl acetate/n-hexane (9:1 v/v) and vortexed for 5 min. After centrifugation (14,000 × g, 5 min, 4 C), the upper layer was collected, evaporated in a nitrogen stream and analysed by HPLC-MS/MS, as described previously (Miralpeix et al, 2019).…”

“…HEK-293T cell endocannabinoids were extracted and measured by HPLC-MS/MS, as previously described (Miralpeix et al, 2019), but with some modifications. Briefly, cells were seeded on a six-well plate and transfected with EV-SYFP2, ABHD6-SYFP2, and CPT1C-SYFP2 using FuGENE HD (Promega, Madrid, Spain).…”

Obesity as a Condition Determined by Food Addiction: Should Brain Endocannabinoid System Alterations Be the Cause and Its Modulation the Solution?

“…Some studies focusing on the hypothalamus have demonstrated that increased endocannabinoid tone in this region is responsible for synaptic remodeling of excitatory and inhibitory synapses, causing the inhibition of anorexigenic neurons and, consequently, hyperphagia and weight gain [99]. Diet-mediated endocannabinoid changes in this region have also been associated with impaired thermogenesis and leptin response activation as a physiological compensatory response [100]. However, recent studies demonstrated that both enhanced endocannabinoid tone and increased CB1 expression in the hypothalamus are transitory and characteristic only of the early phases of exposure to HFD [100].…”