SPP1 and obesity due to melanocortin 4 receptor deficiency: Furthermore, while both WT and OPN-/- mice displayed increased body weights under HFD conditions, the increment was notably less pronounced in OPN-/- mice which suggests that OPN may play a role in fat deposition or the inflammatory responses associated with obesity, as supported by Tardelli et al. (2016) who demonstrated that OPN interacts with pathways involved in adipose tissue expansion and inflammation [44].