PPARGC1A and Endoplasmic Reticulum Stress: We observed that diaphragmatic mRNA expression of PGC-1α was markedly decreased after 12 h of MV, while the inhibition of ER stress by addition of 4-PBA, but not activation of ER stress by addition of TUN, conversely promoted PGC-1α expression (all p < 0.01, Figure 5F).