Phosphodiesterase 3A expression and activity in the murine vasculature is influenced by NO-sensitive guanylyl cyclase.

Phosphodiesterase 3 (PDE3) exists in two isoforms (PDE3A and PDE3B) and is known to act as cGMP-inhibited cAMP-degrading PDE. Therefore, PDE3 may likely be involved in the interaction between the two second messenger pathways. NO-sensitive guanylyl cyclase (NO-GC) is the most important cytosolic generator of cGMP. Here, we investigated the effect of NO-GC deletion on PDE3A-mediated signaling in animals lacking NO-GC either globally (GCKO) or specifically in smooth muscle cells (SMC-GCKO). PDE3A expression is detected in murine aortic smooth muscle, platelets, and heart tissue. Expression and activity of PDE3A in aortae from GCKO and SMC-GCKO mice was reduced by approx. 50% compared to that in control animals. PDE3A downregulation can be linked to the reduction in NO-GC and is not an effect of the increased blood pressure levels resulting from NO-GC deletion. Despite the different PDE3A expression levels, smooth muscle relaxation induced by forskolin to stimulate cAMP signaling was similar in all genotypes. Basal and forskolin-stimulated cAMP levels in aortic tissue were not different between KO and control strains. However, the potency of milrinone, a selective inhibitor of PDE3A, to induce relaxation was higher in aortae from GCKO and SMC-GCKO than that in aorta from control animals. These data were corroborated by the effect of milrinone in vivo, which led to an increase in systolic blood pressure in both KO strains but not in control mice. We conclude that NO-GC modulates PDE3A expression and activity in SMC in vivo conceivably to preserve functional cAMP signaling.

NO-GC in cells 'off the beaten track'.

Nitric oxide-sensitive guanylyl cyclase (NO-GC) has been shown to regulate a plethora of different functions in the body. These include, among many others, the fine-tuning of vascular tone, platelet reactivity and gastrointestinal motility. Evidence for the participation of NO-GC in these functions has been obtained from various species including humans, rodents, as well as insects. Clearly, individual cell types that express NO-GC contribute differentially to organ-specific NO/cGMP signaling in the body. Hence, identification of NO-GC-expressing cells and their individual involvement in NO/cGMP signaling constituted the focus of many studies over the last 40 years. Probably most information has been obtained from vascular smooth muscle cells and platelets, in which NO-GC is known to induce relaxation and inhibition of aggregation, respectively. Many other cell types that express the enzyme have been linked to certain functions, e.g. cardiomyocyte/inotropy or gastrointestinal smooth muscle cells/motility. However, in some cell types, e.g. myofibroblasts or pericytes, NO-GC expression is evident but individual functions of NO/cGMP signaling have yet to be assigned, whereas in other cell types, e.g. in erythrocytes, expression and role of NO-GC is still a matter of debate. This review discusses the current knowledge on 'less popular' cell types that express NO-GC (pericytes, myofibroblasts, cardiomyocytes, adipocytes, interstitial cells of Cajal, fibroblast-like cells and blood cells) and outlines possible further functions in cell types that have not gained strong attention so far.

The enteric nervous system is a potential autoimmune target in multiple sclerosis.

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) in young adults that has serious negative socioeconomic effects. In addition to symptoms caused by CNS pathology, the majority of MS patients frequently exhibit gastrointestinal dysfunction, which was previously either explained by the presence of spinal cord lesions or not directly linked to the autoimmune etiology of the disease. Here, we studied the enteric nervous system (ENS) in a B cell- and antibody-dependent mouse model of MS by immunohistochemistry and electron microscopy at different stages of the disease. ENS degeneration was evident prior to the development of CNS lesions and the onset of neurological deficits in mice. The pathology was antibody mediated and caused a significant decrease in gastrointestinal motility, which was associated with ENS gliosis and neuronal loss. We identified autoantibodies against four potential target antigens derived from enteric glia and/or neurons by immunoprecipitation and mass spectrometry. Antibodies against three of the target antigens were also present in the plasma of MS patients as confirmed by ELISA. The analysis of human colon resectates provided evidence of gliosis and ENS degeneration in MS patients compared to non-MS controls. For the first time, this study establishes a pathomechanistic link between the well-established autoimmune attack on the CNS and ENS pathology in MS, which might provide a paradigm shift in our current understanding of the immunopathogenesis of the disease with broad diagnostic and therapeutic implications.

Cell-specific effects of nitric oxide on the efficiency and frequency of long distance contractions in murine colon.

BACKGROUND: Nitric oxide (NO) mediates inhibitory neurotransmission and is a critical component of neuronal programs that generate propulsive contractions. NO acts via its receptor NO-sensitive guanylyl cyclase (NO-GC) which is expressed in smooth muscle cells (SMC) and interstitial cells of Cajal (ICC). Organ bath studies with colonic rings from NO-GC knockout mice (GCKO) have indicated NO-GC to modulate spontaneous contractions. The cell-specific effects of NO-GC on the dominant pan-colonic propulsive contraction, the long distance contractions (LDCs), of whole colon preparations have not yet been described. METHODS: Contractions of whole colon preparations from wild type (WT), global, and cell-specific GCKO were recorded. After transformation into spatiotemporal maps, motility patterns were analyzed. Simultaneous perfusion of the colon enabled the correlation of outflow with LDCs to analyze contraction efficiency. KEY RESULTS: Deletion of NO-GC in both ICC and SMC (ie, in GCKO and SMC/ICC-GCKO) caused loss of typical LDC activity and instead generated high-frequency LDC-like contractions with inefficient propulsive activity. Frequency was also increased in WT, SMC-GCKO, and ICC-GCKO colon in the presence of L-NAME to block neuronal NO synthase. LDC efficiency was dependent on NO-GC in SMC as it was reduced in GCKO, SMC-GCKO, and ICC/SMC-GCKO colon; LDC efficiency was decreased in all genotypes in the presence of L-NAME. CONCLUSIONS AND INFERENCES: NO/cGMP signaling is critical for normal peristaltic movements; as NO-GC in both SMC and ICC is essential, both cell types appear to work in synchrony. The efficiency of contractions to expel fluid is particularly influenced by NO-GC in SMC.

Integrative Control of Gastrointestinal Motility by Nitric Oxide.

In the gastrointestinal (GI) tract, nitric oxide (NO) has been shown over the last 25 years to exert a prominent function as inhibitory neurotransmitter. Apart from the regulation of secretion and resorption, NO from nitrergic neurons has been demonstrated to be crucial for GI smooth muscle relaxation and motility. In fact, several human diseases such as achalasia, gastroparesis, slow transit constipation or Hirschsprung's disease may involve dysfunctional nitrergic signaling. Most of NO's effects as neurotransmitter are mediated by NO-sensitive guanylyl cyclase (NO-GC) and further transduced by cGMP-dependent mechanisms. In contrast to the vascular system where NO from the endothelium induces relaxation by acting on NO-GC solely in smooth muscle cells, GI tissues contain several different NO-GCexpressing cell types that include smooth muscle cells, interstitial cells of Cajal and fibroblast-like cells. Based on this diverse localization of the NO receptor, the exact pathway(s) leading to NO-induced relaxation are still unknown. Global and cell-specific knockout mouse strains have been generated that lack enzymes participating in nitrergic signaling. These animals have been helpful in examining the role of NO in smooth muscle of the GI tract. Here, we discuss the current knowledge on NO-mediated mechanisms in the relaxation of GI smooth muscle in stomach, small and large intestine including sphincters. Special focus is placed on the integration of nitrergic signals by specialized cell types within the gut smooth muscle layers.