cAMP initiates early phase neuron-like morphology changes and late phase neural differentiation in mesenchymal stem cells.

The intracellular second messenger cAMP is frequently used in induction media to induce mesenchymal stem cells (MSCs) into neural lineage cells. To date, an understanding of the role cAMP exerts on MSCs and whether cAMP can induce MSCs into functional neurons is still lacking. We found cAMP initiated neuron-like morphology changes early and neural differentiation much later. The early phase changes in morphology were due to cell shrinkage, which subsequently rendered some cells apoptotic. While the morphology changes occurred prior to the expression of neural markers, it is not required for neural marker expression and the two processes are differentially regulated downstream of cAMP-activated protein kinase A. cAMP enabled MSCs to gain neural marker expressions with neuronal function, such as, calcium rise in response to neuronal activators, dopamine, glutamate, and potassium chloride. However, only some of the cells induced by cAMP responded to the three neuronal activators and further lack the neuronal morphology, suggesting that although cAMP is able to direct MSCs towards neural differentiation, they do not achieve terminal differentiation.

Synergistic effect of cAMP and palmitate in promoting altered mitochondrial function and cell death in HepG2 cells.

Saturated free fatty acids (FFAs), e.g. palmitate, have long been shown to induce toxicity and cell death in various types of cells. In this study, we demonstrate that cAMP synergistically amplifies the effect of palmitate on the induction of cell death in human hepatocellular carcinoma cell line, HepG2 cells. Elevation of cAMP level in palmitate-treated cells led to enhanced mitochondrial fragmentation, mitochondrial reactive oxygen species (ROS) generation and mitochondrial biogenesis. Mitochondrial fragmentation precedes mitochondrial ROS generation and mitochondrial biogenesis, and may contribute to mitochondrial ROS overproduction and subsequent mitochondrial biogenesis. Fragmentation of mitochondria also facilitated the release of cytotoxic mitochondrial proteins, such as Smac, from the mitochondria and subsequent activation of caspases. However, cell death induced by palmitate and cAMP was caspase-independent and mainly necrotic.