Inhibition of phosphodiesterase-4D reverses memory deficits and depression-like effects via cAMP signaling in mouse models of Alzheimer's disease

Depression is highly correlated with Alzheimer's disease (AD), but treatment for the comorbidity of both is lacking. Phosphodiesterase ‐ 4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP (cAMP), has been considered as a promising target for treatment of both memory loss in AD and depression. Using mouse models of AD and potent PDE4 inhibitors and PDE4‐subtype knockout mice, we demonstrated that PDE4D plays a role in the comorbidity of memory loss and depression in AD. Treatment with the PDE4 inhibitor rolipram or roflumilast reversed memory deficits in novel object recognition and Morris water‐maze tests in APP/PS1 double transgenic and 3xTg‐AD mice, which are widely used models for AD. Similarly, in the tail‐suspension and forced‐swimming tests, the PDE4 inhibitors reversed the decreased immobility in AD mice, suggesting antidepressant‐like effects. The effects of PDE4 inhibitors were mimicked in the tests using mice deficient in PDE4D, which displayed memory‐enhancing and antidepressant‐like effects, relative to the WT mice microinfused with beta‐amyloid peptide 1–42 into the hippocampus. In addition, the PDE4 inhibitor treatment reversed the decreased ratio of Bcl‐2/BAX and inhibited the increased expression of PDE4D in the cerebral cortex and hippocampus of AD mice. Further, the PDE4 inhibitors reversed the decreased levels of cAMP and expression of phosphorylated cAMP response element‐binding protein (CREB) and brain derived neurotrophic factor (BDNF) in AD mice. These were mimicked by PDE4D deficiency and treatment with a PDE4D relatively selective inhibitor. In conclusions, these results suggest that PDE4 is an important target for the comorbidity of memory loss and depression in AD, which appears to be mediated by PDE4D‐cAMP signaling. Support or Funding Information This work was supported by research grants from NIH/NIA AG031687 and NIH/NIAAA HHSN275201700001C (both to HTZ) and the National Natural Science Foundation of China (81441111 to HW) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .