| BackgroudMultiple organ failure in the elderly (MOFE) is often initiated by pulmonary dysfunction. Pulmonary infection accounts for 82.8% of all the precipitating factors of MOFE, which is explained properly after the proposal of "lung motor" hyphthesis. It is pivotal to explore the mechanisms of "lung motor" process for the prevention and treatment of MOFE. Our previous studies indicated that the percentage of apoptosis (APO%) of alveolar macrophages (AM) increased in the aged models of MOFE compared with adult models of MOFE, which might contribute to the uncontrolled pulmonary inflammation and lung injury, and ultimately, MOFE. However, its mechanisms are still obscure. In this research, we analyzed the mitochondria-related apoptosis pathway and other related factors in acute lung injury (ALI) of aged rats, especially the mitochondria-mediated caspase related apoptosis cascade.ObjectiveWe investigated the role of caspase-9 and its related genes in the apoptosis of AM in aged rats with ALI in order to provide theoretical basis for clinical prevention and treatment of MOFE.MethodsIn the first part of this study, artificial accelerated aging rat models were built using D-galactose (D-gal), and then AM was extracted. Morphological features of AM of aged rats were compared with those of adult rats by light and electron microscopes. Meanwhile, serum levels of superoxide dismutase (SOD) and malonaldehyde (MDA) of aged and adult rats were determinded.In the second part of our study, rat AM was cultured with lipopolysac-charide (LPS). APO% of AM was detected at different time points by flow cytometry, and caspase-9 and Apaf-1 mRNA expression were determined by RT-PCR. Also, the expression of Bcl-2 and Bax protein were measured by immunohistochemistry, and the expression of caspase-9 protein was determined by western blotting.ResultsD-gal-induced aged rats showed apparent ageing physical signs. In D-gal-induced aged rats, the activity of serum SOD was decreased and the content of serum MDA was increased (PO.Ol). And we found more particles in AM of group D-gal rats than those of NS group by electron microscope. After interfered by LPS, the apoptotic rate of AM from aged rats began to increase at 0.5 hour and reached the peak at 2 hour, then it begin to decrease. The expression of caspase-9 was also enhanced at 0.5 hour and reached the max at 2 hour. However, the expression of Afaf-1 remained unchanged. The Bcl-2(+) AM was firstly evalutated, then it began to descend with time. But its expression level was still more than that of blank (P<0.05). However, the Bax(+) AM was increased consistently till 4 hours and reached its peak. And the ratio of Bcl-2/Bax rised at 0.5 hour after interference, and then it began to downgrade gradually.Conclusions(1) D-gal can be used to induce aged animal model in rats, its harmful effect on organism was related to reactive oxygen species (ROS). Morphological changes may be a reason that aged rats are susceptibile to develop MOFE after pulmonary infection or ALL (2) Cell apoptosis and the expression of caspase-9 increased after LPS interference, which indicated mitochondria-mediated apoptosis process played a great role in LPS-induced ALI of aged rats. (3)The ratio of Bcl-2/Bax increased at early stage after interference and then decreased, which suggests the ratio of Bcl-2/Bax had a close relation with AM apoptosis ofaged rats.In general, mitochondria regulated AM apoptosis at several levels, which indicated that protecting mitochondria may be a new way to prevent and treat MOFE.
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