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[This corrects the article DOI: 10.7150/thno.39072.].

Aims Cell therapy trials using cardiac-resident progenitor cells (CPCs) and bone marrow-derived mesenchymal stem/progenitor cells (BMCs) in patients after myocardial infarction have provided encouraging results. Exosomes, nanosized extracellular vesicles of endosomal origin, figure prominently in the bioactivities of these cells. However, a head-to-head comparison of exosomes from the two cell types has not been performed yet. Methods and results CPCs and BMCs were derived from cardiac atrial appendage specimens and sternal bone marrow, respectively, from patients (n = 20; age, 69.9 ± 10.9) undergoing heart surgery for aortic valve disease and/or coronary artery disease. Vesicles were purified from cell conditioned media by centrifugation/filtration and ultracentrifugation. Vesicle preparations were predominantly composed of exosomes based on particle size and marker expression (CD9, CD63, CD81, Alix, and TSG-101). CPC-secreted exosomes prevented staurosporine-induced cardiomyocyte apoptosis more effectively than BMC-secreted exosomes. In vivo, CPC-secreted exosomes reduced scar size and improved ventricular function after permanent coronary occlusion in rats more efficiently than BMC-secreted exosomes. Both types of exosomes stimulated blood vessel formation. CPC-secreted exosomes, but not BMC-derived exosomes, enhanced ventricular function after ischaemia/reperfusion. Proteomics profiling identified pregnancy-associated plasma protein-A (PAPP-A) as one of the most highly enriched proteins in CPC vs. BMC exosomes. The active form of PAPP-A was detected on CPC exosome surfaces. These vesicles released insulin-like growth factor-1 (IGF-1) via proteolytic cleavage of IGF-binding protein-4 (IGFBP-4), resulting in IGF-1 receptor activation, intracellular Akt and ERK1/2 phosphorylation, decreased caspase activation, and reduced cardiomyocyte apoptosis. PAPP-A knockdown prevented CPC exosome-mediated cardioprotection both in vitro and in vivo. Conclusion These results suggest that CPC-secreted exosomes may be more cardioprotective than BMC-secreted exosomes, and that PAPP-A-mediated IGF-1 release may explain the benefit. They illustrate a general mechanism whereby exosomes may function via an active protease on their surface, which releases a ligand in proximity to the transmembrane receptor bound by the ligand.

Background Myocardial infarction (MI) is associated with significant loss of cardiomyocytes (CM), which are replaced by a fibrotic scar. Necrotic CM release damage-associated proteins that stimulate innate immune pathways and macrophages (MΦ) tissue infiltration, which drives to the progression of inflammation and myocardial remodeling process. Both, loss of CM and inflammatory response are determinants of the long term ventricle remodeling and heart failure. Circulating inflammatory extracellular vesicles (EV) play a crucial role in the acute and chronic phases of MI, in terms of inflammatory progression. In this study we examined whether reducing the generation of inflammatory EV within few hours from the ischemic event may ameliorate cardiac outcome at short and long time-point in LAD rat model. Methods Before coronary artery ligation, rats were injected IP with a chemical inhibitor of neutral sphingomyelinase (nSMase) which is essential for the biogenesis and release of EVs. The number and size profile of plasma-derived EV was assessed by NTA analysis at baseline and 24hrs after MI. Multiple EV cytokine levels were simultaneously determined using enzyme-linked immunosorbent assay (ELISA)-based protein array technology. Heart global function was assessed by echocardiography and hemodynamic analysis performed at 7, 14 and 28 days after MI. Cytotoxic effects of circulating EV were evaluated ex-vivo in a Langedorff, system by measuring the level of cardiac troponin I (cTnI) in the perfusate. Mechanisms undergoing cytotoxic effects of EV derived from pro-inflammatory MΦ (MΦM1) were studied in vitro into primary rat neonatal CM. Results The induction of MI and the consequent inflammation, dramatically increase the number of circulating EV carrying inflammatory cytokines such as IL1α, ILβ and Rantes. Preventive inhibition nSMase significantly reduced the boost of inflammatory EV and cytokines in treated group as compared to control animals. The reduction of circulating EV post MI results in preserved LV ejection fraction at 7 and 28 days post-MI as compared to control group. Hemodynamic analysis confirmed functional recovery by displaying a higher velocity of LV relaxation and an improved contractility capacity in treated versus control group. The number of infiltrating CD68+ monocytes/macrophages in the infarct area was significantly reduced. Post-MI circulating EV induce cell death in adult CM when added to the perfusate of Langendorff, as assessed by the incresed level of cTnI into media. In vitro MΦM1-EV activated nuclear translocation of NF-kB. Specific inhibition of TLR4 receptor activity abrogated NF-kB translocation and reduced cell death. Indicating that the axis TRL4-NF-kB is essential in EV-mediated CM death. Conclusions Systemic inhibition of EV release during the acute phase of MI preserves heart function in an animal model of LAD. These findings suggest detrimental effects of exosomes in the acute phase of MI.

Cell therapy has been evaluated to enhance heart function after injury. Delivered cells mostly act via paracrine mechanisms, including secreted growth factors, cytokines, and vesicles, such as exosomes (Exo). Intramyocardial injection of cardiac-resident progenitor cells (CPC)-derived Exo reduced scarring and improved cardiac function after myocardial infarction in rats. Here, we explore a clinically relevant approach to enhance the homing process to cardiomyocytes (CM), which is crucial for therapeutic efficacy upon systemic delivery of Exo. By overexpressing exosomal CXCR4, we increased the efficacy of plasmatic injection of cardioprotective Exo-CPC by increasing their bioavailability to ischemic hearts. Intravenous injection of ExoCXCR4 significantly reduced infarct size and improved left ventricle ejection fraction at 4 weeks compared to ExoCTRL (p &lt, 0.01). Hemodynamic measurements showed that ExoCXCR4 improved dp/dt min, as compared to ExoCTRL and PBS group. In vitro, ExoCXCR4 was more bioactive than ExoCTRL in preventing CM death. This in vitro effect was independent from SDF-1α, as shown by using AMD3100 as specific CXCR4 antagonist. We showed, for the first time, that systemic administration of Exo derived from CXCR4-overexpressing CPC improves heart function in a rat model of ischemia reperfusion injury These data represent a substantial step toward clinical application of Exo-based therapeutics in cardiovascular disease.

The paracrine properties of human amniotic membrane-derived mesenchymal stromal cells (hAMCs) have not been fully elucidated. The goal of the present study was to elucidate whether hAMCs can exert beneficial paracrine effects on infarcted rat hearts, in particular through cardioprotection and angiogenesis. Moreover, we aimed to identify the putative active paracrine mediators. hAMCs were isolated, expanded, and characterized. In vitro, conditioned medium from hAMC (hAMC-CM) exhibited cytoprotective and proangiogenic properties. In vivo, injection of hAMC-CM into infarcted rat hearts limited the infarct size, reduced cardiomyocyte apoptosis and ventricular remodeling, and strongly promoted capillary formation at the infarct border zone. Gene array analysis led to the identification of 32 genes encoding for the secreted factors overexpressed by hAMCs. Among these, midkine and secreted protein acidic and rich in cysteine were also upregulated at the protein level. Furthermore, high amounts of several proangiogenic factors were detected in hAMC-CM by cytokine array. Our results strongly support the concept that the administration of hAMC-CM favors the repair process after acute myocardial infarction. Significance The demonstration that stem cells repair infarcted hearts mainly through paracrine mechanisms represents a potential breakthrough. Characterization of therapeutic paracrine mediators could lead to the possibility of treating acute myocardial infarction (AMI) with a single stem cell-derived molecule or a mixture. Compared with cell therapy, this approach would be technically easier to translate to the bedside. An even more straightforward strategy consists of the administration of the entire stem cell secretome (i.e., conditioned medium [CM]). Despite these potential advantages, this approach has not been thoroughly investigated using human cells. This study shows that CM of fetal stromal cells (human amniotic membrane-derived mesenchymal stromal cell [hAMC]-CM), derived from an ethically acceptable source such as the placenta, can repair infarcted hearts without the need for any manipulation. The use of hAMC-CM might be readily translated to the clinical arena in the setting of AMI upon demonstration of its effectiveness in a large animal model.

AIMS: Recent evidence suggests that cardiac progenitor cells (CPCs) may improve cardiac function after injury. The underlying mechanisms are indirect, but their mediators remain unidentified. Exosomes and other secreted membrane vesicles, hereafter collectively referred to as extracellular vesicles (EVs), act as paracrine signalling mediators. Here, we report that EVs secreted by human CPCs are crucial cardioprotective agents. METHODS AND RESULTS: CPCs were derived from atrial appendage explants from patients who underwent heart valve surgery. CPC-conditioned medium (CM) inhibited apoptosis in mouse HL-1 cardiomyocytic cells, while enhancing tube formation in human umbilical vein endothelial cells. These effects were abrogated by depleting CM of EVs. They were reproduced by EVs secreted by CPCs, but not by those secreted by human dermal fibroblasts. Transmission electron microscopy and nanoparticle tracking analysis showed most EVs to be 30-90 nm in diameter, the size of exosomes, although smaller and larger vesicles were also present. MicroRNAs most highly enriched in EVs secreted by CPCs compared with fibroblasts included miR-210, miR-132, and miR-146a-3p. miR-210 down-regulated its known targets, ephrin A3 and PTP1b, inhibiting apoptosis in cardiomyocytic cells. miR-132 down-regulated its target, RasGAP-p120, enhancing tube formation in endothelial cells. Infarcted hearts injected with EVs from CPCs, but not from fibroblasts, exhibited less cardiomyocyte apoptosis, enhanced angiogenesis, and improved LV ejection fraction (0.8 ± 6.8 vs. -21.3 ± 4.5%; P < 0.05) compared with those injected with control medium. CONCLUSION: EVs are the active component of the paracrine secretion by human CPCs. As a cell-free approach, EVs could circumvent many of the limitations of cell transplantation.

Critical limb ischemia (CLI) is burdened by a 40% major amputation rate, and a 5-year life expectancy

Human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes are likely to revolutionize electrophysiological approaches to arrhythmias. Recent evidence suggests the somatic cell origin of hiPSCs may influence their differentiation potential. Owing to their cardiomyogenic potential, cardiac-stromal progenitor cells (CPCs) are an interesting cellular source for generation of hiPSC-derived cardiomyocytes. The effect of ionic current blockade in hiPSC-derived cardiomyocytes generated from CPCs has not been characterized yet.Human-induced pluripotent stem cell-derived cardiomyocytes were generated from adult CPCs and skin fibroblasts from the same individuals. The effect of selective ionic current blockade on spontaneously beating hiPSC-derived cardiomyocytes was assessed using multi-electrode arrays. Cardiac-stromal progenitor cells could be reprogrammed into hiPSCs, then differentiated into hiPSC-derived cardiomyocytes. Human-induced pluripotent stem cell-derived cardiomyocytes of cardiac origin showed higher upregulation of cardiac-specific genes compared with those of fibroblastic origin. Human-induced pluripotent stem cell-derived cardiomyocytes of both somatic cell origins exhibited sensitivity to tetrodotoxin, a blocker of NaIn hiPSC-derived cardiomyocytes of cardiac origin, I

Aim Human-induced pluripotent stem cell (hiPSC)‐derived cardiomyocytes are likely to revolutionize electrophysiological approaches to arrhythmias. Recent evidence suggests the somatic cell origin of hiPSCs may influence their differentiation potential. Owing to their cardiomyogenic potential, cardiac-stromal progenitor cells (CPCs) are an interesting cellular source for generation of hiPSC‐derived cardiomyocytes. The effect of ionic current blockade in hiPSC‐derived cardiomyocytes generated from CPCs has not been characterized yet. Methods and results Human-induced pluripotent stem cell‐derived cardiomyocytes were generated from adult CPCs and skin fibroblasts from the same individuals. The effect of selective ionic current blockade on spontaneously beating hiPSC‐derived cardiomyocytes was assessed using multi-electrode arrays. Cardiac-stromal progenitor cells could be reprogrammed into hiPSCs, then differentiated into hiPSC‐derived cardiomyocytes. Human-induced pluripotent stem cell‐derived cardiomyocytes of cardiac origin showed higher upregulation of cardiac-specific genes compared with those of fibroblastic origin. Human-induced pluripotent stem cell‐derived cardiomyocytes of both somatic cell origins exhibited sensitivity to tetrodotoxin, a blocker of Na+ current ( I Na), nifedipine, a blocker of L-type Ca2+ current ( I CaL), and E4031, a blocker of the rapid component of delayed rectifier K+ current ( I Kr). Human-induced pluripotent stem cell‐derived cardiomyocytes of cardiac origin exhibited sensitivity to JNJ303, a blocker of the slow component of delayed rectifier K+ current ( I Ks). Conclusion In hiPSC‐derived cardiomyocytes of cardiac origin, I Na, I CaL, I Kr, and I Ks were present as tetrodotoxin-, nifedipine-, E4031-, and JNJ303-sensitive currents, respectively. Although cardiac differentiation efficiency was improved in hiPSCs of cardiac vs. non-cardiac origin, no major functional differences were observed between hiPSC‐derived cardiomyocytes of different somatic cell origins. Further studies are warranted to characterize electrophysiological properties of hiPSC‐derived cardiomyocytes generated from CPCs.

Cross-talk between different cell types plays central roles both in cardiac homeostasis and in adaptive responses of the heart to stress. Cardiomyocytes (CMs) send biological messages to the other cell types present in the heart including endothelial cells (ECs) and fibroblasts. In turn, CMs receive messages from these cells. Recent evidence has now established that exosomes, nanosized secreted extracellular vesicles, are crucial mediators of such messages. CMs, ECs, cardiac fibroblasts, and cardiac progenitor cells (CPCs) release exosomes carrying nonrandom subsets of proteins, lipids, and nucleic acids present in their cells of origin. Exosomes secreted from CMs are internalized by fibroblasts and regulate gene expression in these cells as well as in ECs. CPC-derived exosomes protect CMs against apoptosis while also stimulating angiogenesis. They are rich in cardioprotective and proangiogenic microRNAs such as miR-146, miR-210, and miR-132. When injected into infracted heartsin vivo, CPC-derived exosomes reduce infarct size and improve cardiac function. Thus, exosomes are emerging both as key mediators of intercellular communication in the heart and as therapeutic candidates for heart disease.

Erratum to: J. of Cardiovasc. Trans. Res. DOI 10.1007/s12265-014-9601-5. Please note that "Lo Cicero" is the surname of coauthor Viviana Lo Cicero, not "Cicero", as the rendering of this coauthor’s surname at the foot of the title page of the article as published would lead readers to believe.

Several studies have demonstrated that miRNA are involved in cardiac development, stem cell maintenance, and differentiation. In particular, it has been shown that miRNA133, miRNA1, and miRNA499 are involved in progenitor cell differentiation into cardiomyocytes. However, it is unknown whether different miRNA may act synergistically to improve cardiac differentiation. We used mouse P19 cells as a cardiogenic differentiation model. miRNA499, miRNA1, or miRNA133 were transiently over-expressed in P19 cells individually or in different combinations. The over-expression of miRNA499 alone increased the number of beating cells and the association of miRNA499 with miRNA133 exerted a synergistic effect, further increasing the number of beating cells. Real-time polymerase chain reaction showed that the combination of miRNA499 + 133 enhanced the expression of cardiac genes compared with controls. Western blot and immunocytochemistry for connexin43 and cardiac troponin T confirmed these findings. Importantly, caffeine responsiveness, a clear functional parameter of cardiac differentiation, was increased by miRNA499 in association with miRNA133 and was directly correlated with the activation of the cardiac troponin I isoform promoter. Cyclic contractions were reversibly abolished by extracellular calcium depletion, nifedipine, ryanodine, and IP3R blockade. Finally, we demonstrated that the use of miRNA499 + 133 induced cardiac differentiation even in the absence of dimethyl sulfoxide. Our results show that the areas spontaneously contracting possess electrophysiological and pharmacological characteristics compatible with true cardiac excitation-contraction coupling. The translational relevance of our findings was reinforced by the demonstration that the over-expression of miRNA499 and miRNA133 was also able to induce the differentiation of human mesenchymal stromal cells toward the cardiac lineage. Stem Cells 2015;33:1187–1199

Background: We have recently shown that exosomes (Exo), nanosized vesicles secreted by human cardiac progenitor cells (CPC), unlike those released from human dermal fibroblasts (F), are cardioprotective both in vitro and in vivo. Differential expression analyses revealed that Exo-CPC were most highly enriched in miRNA-210, miRNA-132, miRNA-146a-3p, and miR-181 compared to Exo-F. Transcriptional silencing of miR-210 exacerbated stress-induced apoptosis in mouse HL-1 cardiomyocyte (CM)-like cells, whereas miR-210 overexpression was protective via downregulation of ephrin A3 and PTP1b. miR-132 promoted angiogenesis in vitro via downregulation of RasGap-p120. In human CPCs, overexpression of miRNA-132, miRNA-146a-3p and miRNA-181 significantly inhibited stress-induced apoptosis. However, no functional down-regulation of the known target genes for these miRNAs was observed, possibly due species-specific differences.Methods: to test functional effects of these miRNAs in human CMs, we derived induced pluripotent stem (hiPS) cells from both fibroblasts and CPCs. As CPCs are inherently prone to differentiate into CMs, we postulated that CPC-derived hiPS could be advantageous to generate hiPS-derived CMs.Results and conclusions: we were able to show that human CPCs can be reprogrammed to hiPS, and that fully differentiated CMs can be derived from these cells. We are currently being analyzing the molecular and electrophysiological characteristics of CMs from CPC-derived hiPS compared to those of CMs from fibroblast-derived hiPS.

In the gut, 5-HT acts as a paracrine signalling molecule released by enterochromaffin cells and as a transmitter released by some descending serotonergic interneurons. It has a prominent role in the regulation of motility, vascular tone, secretion and perception both in normal and under certain pathophysiological conditions, such as the carcinoid syndrome and the irritable bowel syndrome (IBS). Serotonin is known to markedly influence bowel function by activating at least five receptor types (5-HT(1,2,3,4,7)). Among all 5-HT receptors, those belonging to the 5-HT3 (a ionotropic receptor) and 5-HT4 (a metabotropic receptor) type are the most extensively studied in gastroenterology, resulting in commercially available (although not worldwide) serotonergic agents for the treatment of IBS and functional dyspepsia. Recently, 5-HT7 receptors have been found to participate in the accommodation process of the circular muscle during the preparatory phase of ileal peristalsis. Since an exaggerated accommodation of the gut wall may contribute to abdominal distension and bloating, 5-HT7 receptor ligands may offer innovative opportunities for the pharmacological treatment of functional bowel disorders.

promising new method to treat heart failure but results from clinical trials have been mixed. Here, we present results from our study combining BMMC therapy with coronary bypass surgery (CABG). Materials and methods: First, we enrolled 107 ischemic heart failure patients scheduled for CABG. These patients went through a 4to 12week period with optimized drug therapy. If left ventricular ejection fraction (LVEF) remained 45%, a patient was eligible for the actual study. In a randomized, double-blind manner, the still eligible 39 patients received intramyocardial injections of BMMCs or vehicle intraoperatively into the infarction and border area during CABG. We measured global and segmental LV function and scar size by magnetic resonance imaging (MRI), and viability by positron emission tomography (PET) and singlephoton emission tomography (SPECT), preoperatively and after 1-year follow-up. Results: LVEF, the primary end point measure, improved by a median of 5.6% among controls (IQR 0.2 to 10.1) and by 4.8% in the BMMC patients (IQR -0.5 to 8.2) (P1⁄40.59). Wall thickening in injected segments rose by a median of 4.5% in the control group (IQR -18.1 to 23.9) and by 5.5% in the BMMC patients (IQR -6.6 to 26.5) (P1⁄40.68). Viability by PET and SPECT did not differ between the groups. Myocardial scar volume by MRI in injected segments rose by a median of 5.1% in the control group (IQR -3.3 to 10.8) but fell by 13.1% in the BMMC group (IQR -21.4 to -6.5) (P1⁄40.0002). Conclusions: As an adjunct to CABG, BMMC therapy failed to affect global or local LV systolic function or viability by PET and SPECT during 1-year follow-up. Interestingly, however, it affected one essential prognostic marker: myocardial scar size was significantly reduced by BMMC therapy. Long-term studies are necessary to elucidate this finding’s permanence.

Purpose: The in vivo effects of bone marrow mesenchymal stem cells (BM-MSC) in repairing ischemic hearts are limited by poor engraftment, low differentiation rate and, in elderly patients, by reduced paracrine properties. To overcome these limitations, we genetically engineered BM-MSC with a novel bicistronic lentivirus co-expressing IGF1 and BMP2 (IB), two factors involved in both cardiac differentiation and cytoprotection. Methods: We cloned an IRES-based expression cassette into a novel lentiviral vector. Rat BM-MSC were transduced with a control (GFP-MSC) or IB (IB-MSC) virus. Cardiac differentiation was evaluated by RT-qPCR, western blot, and immunocytochemistry for cardiac specific markers such as GATA4, Nkx2.5, Tbx5, Mef2c, Cx43, cTnT, a-MHC, a-SA and a-SR1. Resistance to hypoxia-induced apoptosis was measured after 24hrs of hypoxia. To study the cytoprotective paracrine properties, H9c2 cells were deprived of oxygen and glucose (6hrs), and then reoxygenated (18hrs) in the presence of control medium (CTRL-M) or medium conditioned by either GFP-MSC (GFP-CM) or IB-MSC (IB-CM). Viability was measured by MTS assay, apoptosis by caspase-3 activation, cytotoxicity by LDH release. Transcriptional levels of known pro- and anti-apoptotic genes were measured by RT-PCR. Activation of I and B associated pathways (Akt, ERK1/2, and SMAD1/5/8) was assessed by western blot. Results: The transduction efficiency with our novel vector was extremely high (>90% with one cycle of infection). Compared with GFP-MSC, IB-MSC triggered expression of cardiac markers both at RNA (Tbx5 +3.8, p

Purpose: It has been demonstrated that miR1 and miR133 are involved in cardiac development and stem cell differentiation, while miR499 enhances the differentiation of embryonic and adult stem cells into cardiomyocytes (CMC). However, it is currently unknown if these miRNA may act synergistically to improve differentiation efficiency. Methods: Mouse P19 cells transduced with a viral vector expressing GFP under the control of a cTnI promoter were primed with 0.5% of DMSO and used as cardiogenic differentiation model (P19 CTRL). MiR499 was transiently over-expressed in P19 cells individually or together with miR1 or miR133. Moreover, we differentiated P19 cells with pre-miR precursors without DMSO. Cardiac differentiation was quantified by: 1) count of spontaneous beating areas; 2) qPCR of the cardiac markers Nkx2.5, GATA4, MEF2c, MLC2v, Cx43 and cTnT; 3) Western Blot and ICC of cTnT and Cx43; 4) measure of inducibility of RyR-mediated Ca++ transients in P19 exposed to caffeine; 5) recording of mechanical activity after Ca++ depletion and in the presence of nifedipine or ryanodine. Results: The overexpression of miR499 alone increased the number of beating CMC by 1.7 fold compared with P19 CTRL (p

Purpose: Mesenchymal stem cells (MSC) derived form human amniotic membrane (A-MSC) differentiate into cardiomyocyte (CMC) more promptly than bone marrow-derived MSC (BM-MSC). Still, the differentiation efficiency is not very high. We found that BM-MSC, particularly from elderly patients, express lower amount of several proteins potentially involved in cardiac differentiation compared with A-MSC. We hypothesized that by overexpressing these factors, cardiac differentiation efficiency of A-MSC may further increase. Methods: Human A-MSC were transduced with a lentiviral vector encoding for either GFP alone (GFP-A-MSC control cells), or TGFβ1 (TGFβ1-A-MSC), or BMP2 (BMP2-A-MSC), or IGF-I (IGF-I-A-MSC), or FGF2 (FGF2-A-MSC). To confirm transduction efficiency, after 48 hours the cells were analyzed by FACS, Western Blot (WB), ELISA and immunocytochemistry (ICC). The cells were then maintained in culture for 5 weeks and analyzed by qPCR, WB and ICC at two different time points: 2 weeks, to search for expression of early cardiac genes (GATA4, Nkx2.5 and Tbx5), and 5 weeks, to verify acquisition of cardiac-specific proteins (Cx43, cTnT and α–MHC). Results: The transduction efficiency with all four lentiviral vectors was higher than 90%. WB, ELISA and ICC confirmed the over-expression of the protein of interest. Compared with GFP-A-MSC, the over-expression of each factor triggered the expression of cardiac markers. qPCR and ICC showed the over-expression of GATA4 and Nkx2.5 in IGF-I-A-MSC and of Tbx5 in TGFβ1-A-MSC and FGF2-A-MSC. qPCR also documented that IGF-I and FGF2 significantly increased the expression levels of Cx43 (+15.8 and +9.5 vs GFP-A-MSC respectively, p

Background & Aims: The 5-hydroxytryptamine 7 (5-HT7) receptors mediate intestinal smooth muscle relaxation. In this study, we evaluated the expression of 5-HT7 receptors in the guinea pig ileum and their role in peristalsis and accommodation of the circular muscle. Methods: We used immunohistochemistry and confocal microscopy with whole tissue and cultured myenteric neurons. Peristalsis was induced by delivering a solution into the oral end of an isolated ileal segment. The effect of the selective 5-HT7 receptor antagonist SB-269970 (100 nmol/L) on peristaltic activity was evaluated at 30, 60, and 90 minutes and compared with control. Results: 5-HT7 receptor immunoreactivity was localized to numerous myenteric neurons, a few submucosal neurons, and a few smooth muscle cells of the ileum. In enteric cultured neurons, 5-HT7 receptor immunoreactivity was observed in subpopulations of after hyperpolarizing neurons and descending neurons as identified by neuron-specific nuclear protein or calbindin and neuronal nitric oxide synthase or vasoactive intestinal peptide antibodies, respectively. SB-269970 significantly increased the threshold pressure by 33.3% ± 2.2% (P < .001) and by 27.2% ± 1.6% (P < .05) at 60 and 90 minutes, respectively, without modifying the threshold volume. The accommodation significantly decreased by 27.5% both at 60 and 90 minutes (P < .05). Conclusions: Our results indicate that endogenous 5-HT is involved in the modulation of circular muscle accommodation during the preparatory phase of peristalsis via the activation of 5-HT7 receptors expressed by neurons in addition to smooth muscle cells. Overstimulation of these receptors leading to an exaggerated accommodation of circular muscle might contribute to abdominal symptoms in functional bowel disorders. © 2005 by the American Gastroenterological Association.