Objectives: Obesity is characterized by excessive fat mass and is associated with serious diseases such as type 2 diabetes. Targeting excess fat mass by sustained lipolysis has been a major challenge for anti-obesity therapies due to unwanted side effects. TLQP-21, a neuropeptide encoded by the pro-peptide VGF (non-acronymic), that binds the complement 3a receptor 1 (C3aR1) on the adipocyte membrane, is emerging as a novel modulator of adipocyte functions and a potential target for obesity-associated diseases. The molecular mechanism is still largely uncharacterized.
Methods: We used a combination of pharmacological and genetic gain and loss of function approaches. 3T3-L1 and mature murine adipocytes were used for in vitro experiments. Chronic in vivo experiments were conducted on diet-induced obese wild type, β1, β2, β3-adrenergic receptor (AR) deficient and C3aR1 knockout mice. Acute in vivo lipolysis experiments were conducted on Sprague Dawley rats.
Results: We demonstrated that TLQP-21 does not possess lipolytic properties per se. Rather, it enhances β-AR activation-induced lipolysis by a mechanism requiring Ca2+ mobilization and ERK activation of Hormone Sensitive Lipase (HSL). TLQP-21 acutely potentiated isoproterenol-induced lipolysis in vivo. Finally, chronic peripheral TLQP-21 treatment decreases body weight and fat mass in diet induced obese mice by a mechanism involving β-adrenergic and C3a receptor activation without associated adverse metabolic effects.
Conclusions: In conclusion, our data identify an alternative pathway modulating lipolysis that could be targeted to diminish fat mass in obesity without the side effects typically observed when using potent pro-lipolytic molecules.
Keywords: Adipocyte; Ca2+; Complement 3a receptor; Isoproterenol; MAPK/ERK; VGF; β-AR.