Involvement of phosphodiesterase 4 in beta-adrenoceptor agonist-induced amylase release in parotid acinar cells

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

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 from 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.

Two Phase Modulation of [Formula: see text] Entry and Cl-/[Formula: see text] Exchanger in Submandibular Glands Cells by Dexmedetomidine

Dexmedetomidine (Dex), a highly selective α2-adrenoceptor agonist, attenuates inflammatory responses induced by lipopolysaccharide (LPS) and induces sedative and analgesic effects. Administration of Dex also reduces salivary secretion in human subjects and inhibits osmotic water permeability in rat cortical collecting ducts. However, little is known about the mechanisms underlying the effects of Dex on salivary glands fluid secretion. We demonstrated the α2-adrenoceptor expression in the basolateral membrane of mouse submandibular glands (SMG). To investigate fluid secretion upon treatment with Dex, we studied the effects of Dex on the activity of Na+-K+-2Cl- cotransporter1 (NKCC1) and Cl-/[Formula: see text] exchange (CBE), and on downstream pro-inflammatory cytokine expression in isolated primary mouse SMG cells. Dex acutely increased CBE activity and NKCC1-mediated and independent [Formula: see text] entry in SMG duct cells, and enhanced ductal fluid secretion in a sealed duct system. Dex showed differential effects on cholinergic/adrenergic stimulations and inflammatory mediators, histamine, and LPS, stimulations-induced Ca2+ in mouse SMG cells. Both, histamine- and LPS-induced intracellular Ca2+ increases were inhibited by Dex, whereas carbachol-stimulated Ca2+ signals were not. Long-lasting (2 h) treatment with Dex reduced CBE activity in SMG and in human submandibular glands (HSG) cells. Moreover, when isolated SMG cells were stimulated with Dex for 2 h, phosphodiesterase 4D (PDE4D) expression was enhanced. These results confirm the anti-inflammatory properties of Dex on LPS-mediated signaling. Further, Dex also inhibited mRNA expression of interleukin-6 and NADPH oxidase 4. The present study also showed that α2-adrenoceptor activation by Dex reduces salivary glands fluid secretion by increasing PDE4D expression, and subsequently reducing the concentration of cAMP. These findings reveal an interaction between the α2-adrenoceptor and PDE4D, which should be considered when using α2-adrenoceptor agonists as sedative or analgesics.

The Regulatory Role of Rolipram on Inflammatory Mediators and Cholinergic/Adrenergic Stimulation-Induced Signals in Isolated Primary Mouse Submandibular Gland Cells

Exposure to bacterial lipopolysaccharides (LPS) induces inflammatory signals in salivary glands. We investigated the regulatory role of phosphodiesterase 4 (PDE4) inhibitor rolipram on inflammatory mediators and cholinergic/adrenergic stimulation-induced intracellular Ca(2+) signaling in salivary acinar and ductal cells. Submandibular gland (SMG) expressed PDE4A through 4D mRNA and PDE4 was localized in the luminal membrane of SMG. LPS induced Ca(2+) signaling and ROS production in SMG. Treatment with rolipram blocked LPS-induced Ca(2+) increase and ROS production. The application of histamine evoked Ca(2+) signals and ROS production, which were attenuated by rolipram in SMG cells. Moreover, LPS-induced NLRP3 inflammasome and cleaved caspase-1 were inhibited by rolipram. The inhibitory role of rolipram in ROS-induced Ca(2+) signaling was mainly observed in acinar cells and not in ductal cells. Rolipram also protected SMG acinar but not ductal cells from LPS-induced cell membrane damage. In the case of cholinergic/adrenergic stimulation, carbachol/isoproterenol-induced Ca(2+) signals were upregulated by the treatment of rolipram in SMG. In the case of cAMP-dependent ductal bicarbonate secretion by rolipram, no effect was observed on the modulation of ductal chloride/bicarbonate exchange activity. Rolipram could suppress the inflammatory signals and could be a potential therapeutic strategy against LPS-induced inflammation to protect the salivary gland cells.

Cyclic nucleotide phosphodiesterases: important signaling modulators and therapeutic targets

By catalyzing hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), cyclic nucleotide phosphodiesterases are critical regulators of their intracellular concentrations and their biological effects. As these intracellular second messengers control many cellular homeostatic processes, dysregulation of their signals and signaling pathways initiate or modulate pathophysiological pathways related to various disease states, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication, chronic obstructive pulmonary disease, and psoriasis. Alterations in expression of PDEs and PDE-gene mutations (especially mutations in PDE6, PDE8B, PDE11A, and PDE4) have been implicated in various diseases and cancer pathologies. PDEs also play important role in formation and function of multimolecular signaling/regulatory complexes, called signalosomes. At specific intracellular locations, individual PDEs, together with pathway-specific signaling molecules, regulators, and effectors, are incorporated into specific signalosomes, where they facilitate and regulate compartmentalization of cyclic nucleotide signaling pathways and specific cellular functions. Currently, only a limited number of PDE inhibitors (PDE3, PDE4, PDE5 inhibitors) are used in clinical practice. Future paths to novel drug discovery include the crystal structure-based design approach, which has resulted in generation of more effective family-selective inhibitors, as well as burgeoning development of strategies to alter compartmentalized cyclic nucleotide signaling pathways by selectively targeting individual PDEs and their signalosome partners.