Notably, despite not being impacted by a 3-month WD, AP1 subunits and heat-shock protein (Hsp) genes Hsp1a, Hsp1b, Hsp1e and Hsp90aa1 were downregulated in the lung aEC population with sustained obesity and in the dietary reversion group (Extended Data Fig. 10m), suggesting that obesity primes the deregulation of stress response genes in this population. Here, FOS is linked to obesity due to melanocortin 4 receptor deficiency.