FIGURE 1.

Catabolic and anabolic pathways. Catabolic or energy consuming processes (e.g., autophagy, proteolysis, mitophagy, etc) are triggered by AMPK. AMPK is activated in conditions of starvation when there are high AMP/ATP and ADP/ATP ratios, and in degenerating tissues or quiescent stem cells. Anabolic or energy building processes (e.g., glycolysis, mitochondrial biogenesis, mitochondrial fission, lipid synthesis) are controlled by growth factor signals, including those that bind receptor tyrosine kinases (RTK). Multiple downstream signals are activated by ligand-bound RTKs including the phosphoinositide-3-kinase (PI3K). PI3K activates the secondary messenger PIP3, a step that PTEN reverses. PIP3 then activates Akt and mTORC1, the latter a metabolic regulator that induces lipid and protein synthesis to drive cellular growth.