Autophagy and apoptosis are critical for controlling Toxoplasma gondii (T. gondii)
infection. T. gondii
infection during pregnancy can damage the fetus and cause
birth defects; however, the molecular mechanisms of this process are poorly understood. This study aims to determine the activities of autophagy and apoptosis as well as their regulatory mechanisms during T. gondii
infection by using human umbilical cord mesenchymal stem cells (hUC-MSCs) as a model of congenital diseases. LC3B, a hallmark
protein of autophagy was incrementally upregulated with the
infection duration, whereas p62 was downregulated in T. gondii-infected hUC-MSCs. Concurrent to this result, the invasion of T. gondii into hUC-MSCs increased in a time-dependent manner. The expression levels of Bcl-2 family
proteins including Bcl-2, Bcl-xL, Bim, Bax, Bid and Bak were not altered; however, Mcl-1 levels in hUC-MSCs were dramatically decreased upon T. gondii
infection. In addition, at 24 h post-
infection, cleaved PARP and cleaved
caspase-3 protein levels were elevated in hUC-MSCs. Importantly, Mcl-1 overexpression reduced the levels of autophagy- and apoptosis-related
proteins in T. gondii-infected hUC-MSCs. Mcl-1
proteins were primarily expressed in the fraction containing mitochondria and strongly interacted with
Beclin-1 under normal conditions; however, these interactions were remarkably attenuated by T. gondii
infection. These results suggest that mitochondrial Mcl-1 is an essential signaling mediator regulating the activation of autophagy and apoptosis during T. gondii
infection.