The cAMP-phosphodiesterase 4 (PDE4) controls β-adrenoceptor- and CFTR-dependent saliva secretion in mice

Abstract

Saliva, while often taken for granted, is indispensable for oral health and overall well-being, as inferred from the significant impairments suffered by patients with salivary gland dysfunction. Here, we show that treatment with several structurally-distinct PAN-PDE4 inhibitors, but not a PDE3 inhibitor, induces saliva secretion in mice, indicating it is a class-effect of PDE4 inhibitors. In anesthetized mice, while neuronal regulations are suppressed, PDE4 inhibition potentiates a β-adrenoceptor-induced salivation, that is ablated by the β-blocker Propranolol and is absent in homozygous ΔF508-CFTR mice lacking functional CFTR. These data suggest that PDE4 acts within salivary glands to gate saliva secretion that is contingent upon the cAMP/PKA-dependent activation of CFTR. Indeed, PDE4 contributes the majority of total cAMP-hydrolytic capacity in submandibular-, sublingual-, and parotid glands, the three major salivary glands of the mouse. In awake mice, PDE4 inhibitor-induced salivation is reduced by CFTR deficiency or β-blockers, but also by the muscarinic blocker Atropine, suggesting an additional, central/neuronal mechanism of PDE4 inhibitor action. The PDE4 family comprises four subtypes, PDE4A-D. Ablation of PDE4D, but not PDE4A-C, produced a minor effect on saliva secretion, implying that while PDE4D may play a predominant role, PDE4 inhibitor-induced salivation results from the concurrent inactivation of multiple (at least two) PDE4 subtypes. Taken together, our data reveal a critical role for PDE4/PDE4D in controlling CFTR function in an in vivo model and in inducing salivation, hinting at a therapeutic potential of PDE4 inhibition for cystic fibrosis and conditions associated with xerostomia.

Non-Selective PDE4 Inhibition Induces a Rapid and Transient Decrease of Serum Potassium in Mice

“…Conversely, when mice were placed under Isoflurane anesthesia for 10 min before PDE4 inhibitor treatment (see scheme in Figure 3 A), there is no longer a difference in body temperature between solvent- and inhibitor-treated mice, given that anesthesia per se induces significant hypothermia ( Figure 3 B). Importantly, the PDE4 inhibitor Roflumilast produces a similar reduction in serum potassium levels in both awake and anesthetized mice (see scheme in Figure 3 C), suggesting that PDE4 inhibitor-induced hypokalemia occurs independent of, and is mechanistically different from, the various nervous system effects associated with PDE4 inhibition in mice [ 31 , 32 , 33 , 34 , 40 ].…”

“…Conversely, as a tight regulation of serum potassium levels is particularly critical for the normal function of excitable cells, such as muscle and nerve cells [ 2 , 3 , 5 , 8 , 58 , 79 , 80 ], it is quite feasible that the PDE4 inhibitor-induced reduction of serum potassium levels itself may affect muscle function and neuronal signaling in the animals and may modulate some of their reported physiologic effects such as hypokinesia (skeletal muscle), gastric retention (smooth muscle), or nervous system effects such as hypothermia or salivation [ 31 , 32 , 33 , 34 ]. Indeed, in multiple experiments, PDE4 inhibitor treatment reduces serum potassium levels in individual animals to at or below 3.5 mmol/L, which represents the lower limit of normal serum potassium levels (homeostatic range is 3.5 to 5.3 mmol/L in humans; [ 2 ]).…”

“…Treatment of mice with PAN-PDE4 inhibitors produces several acute effects, including hypokinesia, hypothermia, and gastroparesis [ 31 , 32 , 33 , 34 ]. As part of our efforts to delineate their underlying mechanisms, blood samples from mice treated with the PDE4 inhibitor Roflumilast were subjected to a basic blood chemistry analysis.…”

Characterization of Transgenic NSG-SGM3 Mouse Model of Precision Radiation-Induced Chronic Hyposalivation

“…Furthermore, several methods of saliva collection from preclinical models after cholinergic stimulation have been reported including direct cannulation of excretory salivary ducts (16), vacuum pump suction of saliva from oral cavity (17), glass capillaries (18), micropipette (19)(20)(21), gravimetry using pre-weighed filter paper strips (22) or a swab method (23). However, the methods such as direct cannulation are associated with risk of injury precluding repeated sampling of the gland, while gravimetry, glass capillary and micropipettebased methods show inter-operator variability (23).…”

Assessment of PDE4 Inhibitor-Induced Hypothermia as a Correlate of Nausea in Mice

“…A multitude of studies have now shown that the genetic knockdown or deletion of individual PDE4 subtypes in cells and/or animals produce unique phenotypes, indicating that each PDE4 subtype exerts unique and non-overlapping roles in the body [ 2 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. Thus, the development of subtype-selective PDE4 inhibitors has been proposed to avert the adverse effects of currently available PAN-PDE4 inhibitors [ 1 , 28 ].…”