Deletion of iRhom2 protects against diet-induced obesity by increasing thermogenesis

Marina Badenes, Abdulbasit Amin, Ismael González-García, Inês Félix, Emma Burbridge, Miguel Cavadas, Francisco José Ortega, Érika de Carvalho, Pedro Faísca, Stefania Carobbio, Elsa Seixas, Dora Pedroso, Ana Neves-Costa, Luís F. Moita, José Manuel Fernández-Real, António Vidal-Puig, Ana Domingos, Miguel López, Colin Adrain

iRhom2 is a polytopic membrane protein that is highly expressed in immune cells, particularly macrophages. iRhom2 is required for the release of tumor necrosis factor (TNF) from myeloid cells. TNF, in turn, regulates the pathobiology of metabolic syndrome in several important ways. Badenes et al. evaluated the contribution of iRhom2 to metabolic syndrome. They report that iRhom2 knockout mice are protected from a range of deleterious metabolic phenotypes including obesity, adipose tissue inflammation, hepatic steatosis, and insulin resistance. Moreover, loss of iRhom2 enhances the capacity of the animals to dissipate excess energy via increased thermogenesis.

Objective: Obesity is the result of positive energy balance. It can be caused by excessive energy consumption but also by decreased energy dissipation, which occurs under several conditions including when the development or activation of brown adipose tissue (BAT) is impaired. Here we evaluated whether iRhom2, the essential cofactor for the Tumour Necrosis Factor (TNF) sheddase ADAM17/TACE, plays a role in the pathophysiology of metabolic syndrome.

Methods: We challenged WT versus iRhom2 KO mice to positive energy balance by chronic exposure to a high fat diet and then compared their metabolic phenotypes. We also carried out ex vivo assays with primary and immortalized mouse brown adipocytes to establish the autonomy of the effect of loss of iRhom2 on thermogenesis and respiration.

Results: Deletion of iRhom2 protected mice from weight gain, dyslipidemia, adipose tissue inflammation, and hepatic steatosis and improved insulin sensitivity when challenged by a high fat diet. Crucially, the loss of iRhom2 promotes thermogenesis via BAT activation and beige adipocyte recruitment, enabling iRhom2 KO mice to dissipate excess energy more efficiently than WT animals. This effect on enhanced thermogenesis is cell-autonomous in brown adipocytes as iRhom2 KOs exhibit elevated UCP1 levels and increased mitochondrial proton leak.

Conclusions: Our data suggest that iRhom2 is a negative regulator of thermogenesis and plays a role in the control of adipose tissue homeostasis during metabolic disease.