NR4A1 and obesity due to melanocortin 4 receptor deficiency: Consistent with the results in the mouse obesity model, PA treatment significantly decreased Hk2 in H9c2 cells, which was upregulated by the inhibition of Nr4a1. The regulatory effect of Nr4a1 was also observed on the protein expression of HK2 in H9c2 cells (Figure 7B,C).