Ablation of specific long PDE4D isoforms increases neurite elongation and conveys protection against amyloid-ß pathology.

Inhibition of phosphodiesterase 4D (PDE4D) enzymes has been investigated as therapeutic strategy to treat memory problems in Alzheimer's disease (AD). Although PDE4D inhibitors are effective in enhancing memory processes in rodents and humans, severe side effects may hamper their clinical use. PDE4D enzymes comprise different isoforms, which, when targeted specifically, can increase treatment efficacy and safety. The function of PDE4D isoforms in AD and in molecular memory processes per se has remained unresolved. Here, we report the upregulation of specific PDE4D isoforms in transgenic AD mice and hippocampal neurons exposed to amyloid-ß. Furthermore, by means of pharmacological inhibition and CRISPR-Cas9 knockdown, we show that the long-form PDE4D3, -D5, -D7, and -D9 isoforms regulate neuronal plasticity and convey resilience against amyloid-ß in vitro. These results indicate that isoform-specific, next to non-selective, PDE4D inhibition is efficient in promoting neuroplasticity in an AD context. Therapeutic effects of non-selective PDE4D inhibitors are likely achieved through actions on long isoforms. Future research should identify which long PDE4D isoforms should be specifically targeted in vivo to both improve treatment efficacy and reduce side effects.

MBTPS2 acts as a regulator of lipogenesis and cholesterol synthesis through SREBP signalling in prostate cancer.

BACKGROUND: Prostate cancer is the most common cancer in men in the developed world, with most deaths caused by advanced and metastatic disease which has no curative options. Here, we identified Mbtps2 alteration to be associated with metastatic disease in an unbiased in vivo screen and demonstrated its regulation of fatty acid and cholesterol metabolism. METHODS: The Sleeping Beauty transposon system was used to randomly alter gene expression in the PtenNull murine prostate. MBTPS2 was knocked down by siRNA in LNCaP, DU145 and PC3 cell lines, which were then phenotypically investigated. RNA-Seq was performed on LNCaP cells lacking MBTPS2, and pathways validated by qPCR. Cholesterol metabolism was investigated by Filipin III staining. RESULTS: Mbtps2 was identified in our transposon-mediated in vivo screen to be associated with metastatic prostate cancer. Silencing of MBTPS2 expression in LNCaP, DU145 and PC3 human prostate cancer cells reduced proliferation and colony forming growth in vitro. Knockdown of MBTPS2 expression in LNCaP cells impaired cholesterol synthesis and uptake along with reduced expression of key regulators of fatty acid synthesis, namely FASN and ACACA. CONCLUSION: MBTPS2 is implicated in progressive prostate cancer and may mechanistically involve its effects on fatty acid and cholesterol metabolism.

SUMOylation does not affect cardiac troponin I stability but alters indirectly the development of force in response to Ca2.

Post-translational modification of the myofilament protein troponin I by phosphorylation is known to trigger functional changes that support enhanced contraction and relaxation of the heart. We report for the first time that human troponin I can also be modified by SUMOylation at lysine 177. Functionally, TnI SUMOylation is not a factor in the development of passive and maximal force generation in response to calcium, however this modification seems to act indirectly by preventing SUMOylation of other myofilament proteins to alter calcium sensitivity and cooperativity of myofilaments. Utilising a novel, custom SUMO site-specific antibody that recognises only the SUMOylated form of troponin I, we verify that this modification occurs in human heart and that it is upregulated during disease.

Phosphodiesterase type 4 anchoring regulates cAMP signaling to Popeye domain-containing proteins.

Cyclic AMP is a ubiquitous second messenger used to transduce intracellular signals from a variety of Gs-coupled receptors. Compartmentalisation of protein intermediates within the cAMP signaling pathway underpins receptor-specific responses. The cAMP effector proteins protein-kinase A and EPAC are found in complexes that also contain phosphodiesterases whose presence ensures a coordinated cellular response to receptor activation events. Popeye domain containing (POPDC) proteins are the most recent class of cAMP effectors to be identified and have crucial roles in cardiac pacemaking and conduction. We report the first observation that POPDC proteins exist in complexes with members of the PDE4 family in cardiac myocytes. We show that POPDC1 preferentially binds the PDE4A sub-family via a specificity motif in the PDE4 UCR1 region and that PDE4s bind to the Popeye domain of POPDC1 in a region known to be susceptible to a mutation that causes human disease. Using a cell-permeable disruptor peptide that displaces the POPDC1-PDE4 complex we show that PDE4 activity localized to POPDC1 modulates cycle length of spontaneous Ca2+ transients firing in intact mouse sinoatrial nodes.

Phosphodiesterase 4B: Master Regulator of Brain Signaling.

Phosphodiesterases (PDEs) are the only superfamily of enzymes that have the ability to break down cyclic nucleotides and, as such, they have a pivotal role in neurological disease and brain development. PDEs have a modular structure that allows targeting of individual isoforms to discrete brain locations and it is often the location of a PDE that shapes its cellular function. Many of the eleven different families of PDEs have been associated with specific diseases. However, we evaluate the evidence, which suggests the activity from a sub-family of the PDE4 family, namely PDE4B, underpins a range of important functions in the brain that positions the PDE4B enzymes as a therapeutic target for a diverse collection of indications, such as, schizophrenia, neuroinflammation, and cognitive function.

Understanding PDE4's function in Alzheimer's disease; a target for novel therapeutic approaches.

Phosphodiesterases (PDEs) have long been considered as targets for the treatment of Alzheimer's disease (AD) and a substantial body of evidence suggests that one sub-family from the super-family of PDEs, namely PDE4D, has particular significance in this context. This review discusses the role of PDE4 in the orchestration of cAMP response element binding signaling in AD and outlines the benefits of targeting PDE4D specifically. We examine the limited available literature that suggests PDE4 expression does not change in AD brains together with reports that show PDE4 inhibition as an effective treatment in this age-related neurodegenerative disease. Actually, aging induces changes in PDE4 expression/activity in an isoform and brain-region specific manner that proposes a similar complexity in AD brains. Therefore, a more detailed account of AD-related alterations in cellular/tissue location and the activation status of PDE4 is required before novel therapies can be developed to target cAMP signaling in this disease.

Methods to Investigate Arrestins in Complex with Phosphodiesterases.

The many functions of ß-arrestin proteins in the desensitization of G-protein-coupled receptors have been well characterized; however, the discovery that this scaffold protein could actually recruit phosphodiesterases (PDEs) to the site of cAMP synthesis changed the way researchers thought about the static nature of precisely localized cAMP hydrolysis by anchored PDEs. Before this discovery, the compartmentalization of cAMP gradients formed by the activation of specific receptors was generally understood to be underpinned by highly localized pools of specific PDEs that were anchored by large static anchors such as A-kinase-anchoring proteins (AKAPs). Such anchors acted to position cAMP effector proteins such as protein kinase A (PKA) and exchange protein directly activated by cAMP (EPAC) in places that would allow cAMP concentrations to breach their activation threshold only when a specific receptor activation occurred. In this arrangement PDEs acted as local "sinks" for cAMP and this enforced receptor-specific function by allowing the correct activation of a distinct pool of cAMP effectors in precise localizations. The discovery that ß-arrestin could shuttle cAMP hydrolyzing activity to the membrane shortly after receptor activation added to the complexity of this process by restricting cAMP diffusion into the cell interior for some receptors. This chapter describes the methods used to identify, confirm, and test the function of PDE-ß-arrestin complexes.