Normal pressure hydrocephalus and cognitive impairment: The gait phenotype matters too.

BACKGROUND AND PURPOSE: Idiopathic normal pressure hydrocephalus (iNPH) is a chronic neurological disease resulting in progressive gait and cognitive disorders. We investigated whether the gait phenotype is associated with the severity of cognitive deficits in iNPH. METHODS: This retrospective study recruited 88 patients (mean age = 76.18 ± 7.21 years, 42% female). Patients were initially referred for suspicion of iNPH and underwent a comprehensive analysis, including gait analysis and cognitive evaluation. RESULTS: In this cohort (27% normal gait, 25% frontal gait, 16% parkinsonian gait, 27% other gait abnormalities), patients with parkinsonian and frontal gait had the lowest Mini-Mental State Examination (MMSE) scores and the slowest gait speed. Patients with normal gait had the highest MMSE scores and gait speed. Frontal gait was associated with lower MMSE score, even after adjusting for age, gender, comorbidities, white matter lesions, and education level (ß = -0.221 [95% confidence interval (CI) = -3.718 to -0.150], p = 0.034). Normal gait was associated with the best MMSE scores, even after adjusting for the abovementioned variables (ß = 0.231 [95% CI = 0.124-3.639], p = 0.036). CONCLUSIONS: Gait phenotypes among iNPH patients are linked to global cognition as assessed with MMSE.

Normal pressure hydrocephalus and CSF tap test response: the gait phenotype matters.

This study compared gait speed changes after CSF tap test in patients with idiopathic normal pressure hydrocephalus presenting with various gait phenotypes (frontal, parkinsonian, normal, or other). All patients improved, except those with parkinsonian gait.

Specific Activation of the Alternative Cardiac Promoter of Cacna1c by the Mineralocorticoid Receptor.

RATIONALE: The MR (mineralocorticoid receptor) antagonists belong to the current therapeutic armamentarium for the management of cardiovascular diseases, but the mechanisms conferring their beneficial effects are poorly understood. Part of the cardiovascular effects of MR is because of the regulation of L-type Cav1.2 Ca2+ channel expression, which is generated by tissue-specific alternative promoters as a long cardiac or short vascular N-terminal transcripts. OBJECTIVE: To analyze the molecular mechanisms by which aldosterone, through MR, modulates Cav1.2 expression and function in a tissue-specific manner. METHODS AND RESULTS: In primary cultures of neonatal rat ventricular myocytes, aldosterone exposure for 24 hours increased in a concentration-dependent manner long cardiac Cav1.2 N-terminal transcripts expression at both mRNA and protein levels, correlating with enhanced concentration-, time-, and MR-dependent P1-promoter activity. In silico analysis and mutagenesis identified MR interaction with both specific activating and repressing DNA-binding elements on the P1-promoter. The relevance of this regulation is confirmed both ex and in vivo in transgenic mice harboring the luciferase reporter gene under the control of the cardiac P1-promoter. Moreover, we show that this cis-regulatory mechanism is not limited to the heart. Indeed, in smooth muscle cells from different vascular beds, in which the short vascular Cav1.2 N-terminal transcripts is normally the major isoform, we found that MR signaling activates long cardiac Cav1.2 N-terminal transcripts expression through P1-promoter activation, leading to vascular contractile dysfunction. These results were further corroborated in hypertensive aldosterone/salt rodent models, showing notably a positive correlation between blood pressure and cardiac P1-promoter activity in aorta. This new vascular long cardiac Cav1.2 N-terminal transcripts molecular signature reduced sensitivity to the Ca2+ channel blocker, nifedipine, in aldosterone-treated vessels. CONCLUSIONS: Our results reveal that MR acts as a transcription factor to translate aldosterone signal into specific cardiac P1-promoter activation that might influence the therapeutic outcome of cardiovascular diseases.

Progression of excitation-contraction coupling defects in doxorubicin cardiotoxicity.

Cardiac failure is a common complication in cancer survivors treated with anthracyclines. Here we followed up cardiac function and excitation-contraction (EC) coupling in an in vivo doxorubicin (Dox) treated mice model (iv, total dose of 10 mg/Kg divided once every three days). Cardiac function was evaluated by echocardiography at 2, 6 and 15 weeks after the last injection. While normal at 2 and 6 weeks, ejection fraction was significantly reduced at 15 weeks. In order to evaluate the underlying mechanisms, we measured [Ca2+]i transients by confocal microscopy and action potentials (AP) by patch-clamp technique in cardiomyocytes isolated at these times. Three phases were observed: 1/depression and slowing of the [Ca2+]i transients at 2 weeks after treatment, with occurrence of proarrhythmogenic Ca2+ waves, 2/compensatory state at 6 weeks, and 3/depression on [Ca2+]i transients and cell contraction at 15 weeks, concomitant with in-vivo defects. These [Ca2+]i transient alterations were observed without cellular hypertrophy or AP prolongation and mirrored the sarcoplasmic reticulum (SR) Ca2+ load variations. At the molecular level, this was associated with a decrease in the sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) expression and enhanced RyR2 phosphorylation at the protein kinase A (PKA, pS2808) site (2 and 15 weeks). RyR2 phosphorylation at the Ca2+/calmodulin dependent protein kinase II (CaMKII, pS2814) site was enhanced only at 2 weeks, coinciding with the higher incidence of proarrhythmogenic Ca2+ waves. Our study highlighted, for the first time, the progression of Dox treatment-induced alterations in Ca2+ handling and identified key components of the underlying Dox cardiotoxicity. These findings should be helpful to understand the early-, intermediate-, and late- cardiotoxicity already recorded in clinic in order to prevent or treat at the subclinical level.

Carabin protects against cardiac hypertrophy by blocking calcineurin, Ras, and Ca2+/calmodulin-dependent protein kinase II signaling.

BACKGROUND: Cardiac hypertrophy is an early hallmark during the clinical course of heart failure and is regulated by various signaling pathways. However, the molecular mechanisms that negatively regulate these signal transduction pathways remain poorly understood. METHODS AND RESULTS: Here, we characterized Carabin, a protein expressed in cardiomyocytes that was downregulated in cardiac hypertrophy and human heart failure. Four weeks after transverse aortic constriction, Carabin-deficient (Carabin(-/-)) mice developed exaggerated cardiac hypertrophy and displayed a strong decrease in fractional shortening (14.6±1.6% versus 27.6±1.4% in wild type plus transverse aortic constriction mice; P<0.0001). Conversely, compensation of Carabin loss through a cardiotropic adeno-associated viral vector encoding Carabin prevented transverse aortic constriction-induced cardiac hypertrophy with preserved fractional shortening (39.9±1.2% versus 25.9±2.6% in control plus transverse aortic constriction mice; P<0.0001). Carabin also conferred protection against adrenergic receptor-induced hypertrophy in isolated cardiomyocytes. Mechanistically, Carabin carries out a tripartite suppressive function. Indeed, Carabin, through its calcineurin-interacting site and Ras/Rab GTPase-activating protein domain, functions as an endogenous inhibitor of calcineurin and Ras/extracellular signal-regulated kinase prohypertrophic signaling. Moreover, Carabin reduced Ca(2+)/calmodulin-dependent protein kinase II activation and prevented nuclear export of histone deacetylase 4 after adrenergic stimulation or myocardial pressure overload. Finally, we showed that Carabin Ras-GTPase-activating protein domain and calcineurin-interacting domain were both involved in the antihypertrophic action of Carabin. CONCLUSIONS: Our study identifies Carabin as a negative regulator of key prohypertrophic signaling molecules, calcineurin, Ras, and Ca(2+)/calmodulin-dependent protein kinase II and implicates Carabin in the development of cardiac hypertrophy and failure.

Epac in cardiac calcium signaling.

Epac, exchange protein directly activated by cAMP, is emerging as a new regulator of cardiac physiopathology. Although its effects are much less known than the classical cAMP effector, PKA, several studies have investigated the cardiac role of Epac, providing evidences that Epac modulates intracellular Ca(2+). In one of the first analyses, it was shown that Epac can increase the frequency of spontaneous Ca(2+) oscillations in cultured rat cardiomyocytes. Later on, in adult cardiomyocytes, it was shown that Epac can induce sarcoplasmic reticulum (SR) Ca(2+) release in a PKA independent manner. The pathway identified involved phospholipase C (PLC) and Ca(2+)/calmodulin kinase II (CaMKII). The latter phosphorylates the ryanodine receptor (RyR), increasing the Ca(2+) spark probability. The RyR, Ca(2+) release channel located in the SR membrane, is a key element in the excitation-contraction coupling. Thus Epac participates in the excitation-contraction coupling. Moreover, by inducing RyR phosphorylation, Epac is arrhythmogenic. A detailed analysis of Ca(2+) mobilization in different microdomains showed that Epac preferently elevated Ca(2+) in the nucleoplasm ([Ca(2+)]n). This effect, besides PLC and CaMKII, required inositol 1,4,5 trisphosphate receptor (IP3R) activation. IP3R is other Ca(2+) release channel located mainly in the perinuclear area in the adult ventricular myocytes, where it has been shown to participate in the excitation-transcription coupling (the process by which Ca(2+) activates transcription). If Epac activation is maintained for some time, the histone deacetylase (HDAC) is translocated out of the nucleus de-repressing the transcription factor myocyte enhancer factor (MEF2). These evidences also pointed to Epac role in activating the excitation-transcription coupling. In fact, it has been shown that Epac induces cardiomyocyte hypertrophy. Epac activation for several hours, even before the cell hypertrophies, induces a profound modulation of the excitation-contraction coupling: increasing the [Ca(2+)]i transient amplitude and cellular contraction. Thus Epac actions are rapid but time and microdomain dependent in the cardiac myocyte. Taken together the results collected indicate that Epac may have an important role in the cardiac response to stress.

EPAC1 inhibition protects the heart from doxorubicin-induced toxicity.

Anthracyclines, such as doxorubicin (Dox), are widely used chemotherapeutic agents for the treatment of solid tumors and hematologic malignancies. However, they frequently induce cardiotoxicity leading to dilated cardiomyopathy and heart failure. This study sought to investigate the role of the exchange protein directly activated by cAMP (EPAC) in Dox-induced cardiotoxicity and the potential cardioprotective effects of EPAC inhibition. We show that Dox induces DNA damage and cardiomyocyte cell death with apoptotic features. Dox also led to an increase in both cAMP concentration and EPAC1 activity. The pharmacological inhibition of EPAC1 (with CE3F4) but not EPAC2 alleviated the whole Dox-induced pattern of alterations. When administered in vivo, Dox-treated WT mice developed a dilated cardiomyopathy which was totally prevented in EPAC1 knock-out (KO) mice. Moreover, EPAC1 inhibition potentiated Dox-induced cell death in several human cancer cell lines. Thus, EPAC1 inhibition appears as a potential therapeutic strategy to limit Dox-induced cardiomyopathy without interfering with its antitumoral activity.

Epac enhances excitation-transcription coupling in cardiac myocytes.

Epac is a guanine nucleotide exchange protein that is directly activated by cAMP, but whose cardiac cellular functions remain unclear. It is important to understand cardiac Epac signaling, because it is activated in parallel to classical cAMP-dependent signaling via protein kinase A. In addition to activating contraction, Ca(2+) is a key cardiac transcription regulator (excitation-transcription coupling). It is unknown how myocyte Ca(2+) signals are decoded in cardiac myocytes to control nuclear transcription. We examine Epac actions on cytosolic ([Ca(2+)](i)) and intranuclear ([Ca(2+)](n)) Ca(2+) homeostasis, focusing on whether Epac alters [Ca(2+)](n) and activates a prohypertrophic program in cardiomyocytes. Adult rat cardiomyocytes, loaded with fluo-3 were viewed by confocal microscopy during electrical field stimulation at 1Hz. Acute Epac activation by 8-pCPT increased Ca(2+) sparks and diastolic [Ca(2+)](i), but decreased systolic [Ca(2+)](i). The effects on diastolic [Ca(2+)](i) and Ca(2+) spark frequency were dependent on phospholipase C (PLC), inositol 1,4,5 triphosphate receptor (IP(3)R) and CaMKII activation. Interestingly, Epac preferentially increased [Ca(2+)](n) during both diastole and systole, correlating with the perinuclear expression pattern of Epac. Moreover, Epac activation induced histone deacetylase 5 (HDAC5) nuclear export, with consequent activation of the prohypertrophic transcription factor MEF2. These data provide the first evidence that the cAMP-binding protein Epac modulates cardiac nuclear Ca(2+) signaling by increasing [Ca(2+)](n) through PLC, IP(3)R and CaMKII activation, and initiates a prohypertrophic program via HDAC5 nuclear export and subsequent activation of the transcription factor MEF2.

Role of the cAMP-binding protein Epac in cardiovascular physiology and pathophysiology.

Exchange proteins directly activated by cyclic AMP (Epac) were discovered 10 years ago as new sensors for the second messenger cyclic AMP (cAMP). Epac family, including Epac1 and Epac2, are guanine nucleotide exchange factors for the Ras-like small GTPases Rap1 and Rap2 and function independently of protein kinase A. Given the importance of cAMP in the cardiovascular system, numerous molecular and cellular studies using specific Epac agonists have analyzed the role and the regulation of Epac proteins in cardiovascular physiology and pathophysiology. The specific functions of Epac proteins may depend upon their microcellular environments as well as their expression and localization. This review discusses recent data showing the involvement of Epac in vascular cell migration, endothelial permeability, and inflammation through specific signaling pathways. In addition, we present evidence that Epac regulates the activity of various cellular compartments of the cardiac myocyte and influences calcium handling and excitation-contraction coupling. The potential role of Epac in cardiovascular disorders such as cardiac hypertrophy and remodeling is also discussed.

Epac stimulation induces rapid increases in connexin43 phosphorylation and function without preconditioning effect.

It has been recently shown that beta-adrenergic receptors are able to activate phospholipase C via the cyclic adenosine monophosphate-binding protein Epac. This new interconnection may participate in isoproterenol (Iso)-induced preconditioning. We evaluated here whether Epac could induce PKCepsilon activation and could play a role in ischemic preconditioning through the phosphorylation of connexin43 (Cx43) and changes in gap junctional intercellular communication (GJIC). In cultured rat neonatal cardiomyocytes, we showed that in response to Iso and 8-CPT, a specific Epac activator, PKCepsilon content was increased in particulate fractions of cell lysates independently of protein kinase A (PKA). This was associated with an increased Cx43 phosphorylation. Both Iso and 8-CPT induced an increase in GJIC that was blocked by the PKC inhibitor bisindolylmaleimide. Interestingly, inhibition of PKA partly suppressed both Iso-induced increases in Cx43 phosphorylation and in GJIC. The same PKCepsilon-dependent Cx43 phosphorylation by beta-adrenergic stimulation via Epac was found in adult rat hearts. However, in contrast with Iso that induced a preconditioning effect, perfusion of isolated hearts with 8-CPT prior to ischemia failed to improve the post-ischemia functional recovery. In conclusion, Epac stimulation induces PKCepsilon activation and Cx43 phosphorylation with an increase in GJIC, but Epac activation does not induce preconditioning to ischemia in contrast with beta-adrenergic stimulation.

Epac mediates beta-adrenergic receptor-induced cardiomyocyte hypertrophy.

Cardiac hypertrophy is promoted by adrenergic overactivation and can progress to heart failure, a leading cause of mortality worldwide. Although cAMP is among the most well-known signaling molecules produced by beta-adrenergic receptor stimulation, its mechanism of action in cardiac hypertrophy is not fully understood. The identification of Epac (exchange protein directly activated by cAMP) proteins as novel sensors for cAMP has broken the dogma surrounding cAMP and protein kinase A. However, their role and regulation in the mature heart remain to be defined. Here, we show that cardiac hypertrophy induced by thoracic aortic constriction increases Epac1 expression in rat myocardium. Adult ventricular myocytes isolated from banded animals display an exaggerated cellular growth in response to Epac activation. At the molecular level, Epac1 hypertrophic effects are independent of its classic effector, Rap1, but rather involve the small GTPase Ras, the phosphatase calcineurin, and Ca(2+)/calmodulin-dependent protein kinase II. Importantly, we find that in response to beta-adrenergic receptor stimulation, Epac1 activates Ras and induces adult cardiomyocyte hypertrophy in a cAMP-dependent but protein kinase A-independent manner. Knockdown of Epac1 strongly reduces beta-adrenergic receptor-induced hypertrophic program. Finally, we report for the first time that Epac1 is mainly expressed in human heart as compared with Epac2 isoform and is increased in heart failure. Taken together, our data demonstrate that the guanine nucleotide exchange factor Epac1 contributes to the hypertrophic effect of beta-adrenergic receptor in a protein kinase A-independent fashion and may, therefore, represent a novel therapeutic target for the treatment of cardiac disorders.

Parkinsonian gait in aging: A feature of Alzheimer's pathology?

INTRODUCTION: Central neurological gait abnormalities (CNGA; i.e. frontal or parkinsonian) are frequently associated with neurodegenerative conditions in older adults, but their pathophysiological substrates remain poorly described. This cross-sectional study aims to assess the association between cerebrospinal fluid (CSF) Alzheimer's biomarkers and CNGA. METHODS: CSF biomarkers (phosphor-tau, total tau and Aß1-42) were measured in 52 patients with CNGA (77.33 ± 6.09 years; 28.8% female). Gait phenotypes were evaluated by two diagnosis-blinded assessors and classified as frontal gait, parkinsonian gait or other gait abnormalities. RESULTS: Parkinsonian gait was significantly associated with a decreased CSF Aß42 even after adjusting on age, gender, comorbidities and white matter changes (ß: -0.32; 95% CI: [-340.6; -22.9]; p value: 0.026). Phosphor-tau and total tau were not associated with any other CNGA (i.e. frontal gait and other gait abnormalities). DISCUSSION: Parkinsonian gait represents a gait phenotype of Alzheimer's pathology in patients with CNGA.

Functional characterization of the cAMP-binding proteins Epac in cardiac myocytes.

The cyclic AMP (cAMP)-binding proteins, Epac, are guanine nucleotide exchange factors for the Ras-like small GTPases. Since their discovery in 1998 and with the development of specific Epac agonists, many data in the literature have illustrated their critical role in multiple cellular events mediated by the second messenger cAMP. Given the importance of cAMP in cardiovascular physiology and physiopathology, there is a growing interest to delineate the role of these multi-domain Epac in the cardiovascular system. This review will focus on recent pharmacological and biochemical studies aiming at understanding the role of Epac in cardiomyocyte signaling and hypertrophy.

Is frontal gait a myth in normal pressure hydrocephalus?

BACKGROUND: Patients with idiopathic normal pressure hydrocephalus (iNPH) are considered to present a magnetic, slow, wide-based gait, also called frontal gait. However, this gait profile is not specific for iNPH and encountered in patients with other neurological conditions mimicking iNPH (i.e. iNPH mimics), such as vascular dementia. We aimed to characterize the gait profiles in iNPH and their mimics and to compare the prevalence of clinical gait abnormalities between both groups. METHODS: This retrospective study included 140 patients suspected of iNPH (76.3 ±â€¯6.8 yo; 30.7% female). Eighty patients (57.1%) were diagnosed with iNPH according to the NPH consensus guidelines criteria; the remaining sixty patients were classified as mimics (23 neurodegenerative conditions, 12 multifactorial conditions, 9 vascular dementia, 7 mixed dementias, 6 toxic conditions, 2 psychiatric conditions, and 1 stroke). Two independent diagnosis-blinded clinicians (kappa, 0.73) evaluated gait according to four categories: frontal gait, parkinsonian gait, other clinical gait abnormalities, and normal gait. RESULTS: iNPH patients and mimics shared similar clinical characteristics. Frontal gait occurred in only 26% of patients (with a similar prevalence for the mimics). Parkinsonian gait was significantly more prevalent among the mimics (32% versus 15%; p-value: 0.032). This association between parkinsonian gait and mimics remained significant after adjusting for age, gender, comorbidities and white matter changes (OR: 2.404; 95% CI: [1.03-5.64]; p value: 0.044). CONCLUSION: Frontal gait is not the most prevalent gait abnormality in iNPH and does not discriminate iNPH from its mimics. Parkinsonian gait is more prevalent among the mimics.

Small GTP-binding proteins and their regulators in cardiac hypertrophy.

Small GTP-binding proteins (small G proteins) act as GDP-GTP-regulated molecular switches and are activated by guanine nucleotide exchange factors (GEFs) in response to diverse extracellular stimuli. During this last decade, numerous molecular and cellular studies, as well as genetically-modified animal models, have highlighted the role of small G proteins in the regulation of cardiac hypertrophy. The growing interest in small G protein signalling comes from the fact that chronic hypertrophic response is considered maladaptive and predisposes individuals to heart failure. Although some of the hypertrophic signalling pathways involving small G proteins have now been identified, a central question deals with the identity of the GEFs that modulate small G protein activation in the context of cardiac hypertrophy. Here, we discuss the precise regulation of Ras and Rho subfamilies of GTPases by GEFs and other regulatory proteins during cardiac hypertrophy. In addition, we summarize recent published data, mainly those describing the role of small G proteins in the development of myocardial hypertrophy and we further present the importance of their downstream effectors in myocardial remodelling.

cAMP-binding protein Epac induces cardiomyocyte hypertrophy.

cAMP is one of the most important second messenger in the heart. The discovery of Epac as a guanine exchange factor (GEF), which is directly activated by cAMP, raises the question of the role of this protein in cardiac cells. Here we show that Epac activation leads to morphological changes and induces expression of cardiac hypertrophic markers. This process is associated with a Ca2+-dependent activation of the small GTPase, Rac. In addition, we found that Epac activates a prohypertrophic signaling pathway, which involves the Ca2+ sensitive phosphatase, calcineurin, and its primary downstream effector, NFAT. Rac is involved in Epac-induced NFAT dependent cardiomyocyte hypertrophy. Blockade of either calcineurin or Rac activity blunts the hypertrophic response elicited by Epac indicating these signaling molecules coordinately regulate cardiac gene expression and cellular growth. Our results thus open new insights into the signaling pathways by which cAMP may mediate its biological effects and identify Epac as a new positive regulator of cardiac growth.

Gait Profile Score in multiple sclerosis patients with low disability.

BACKGROUND: Gait abnormalities are subtle in multiple sclerosis (MS) patients with low disability and need to be better determined. As a biomechanical approach, the Gait Profile Score (GPS) is used to assess gait quality by combining nine gait kinematic variables in one single value. This study aims i) to establish if the GPS can detect gait impairments and ii) to compare GPS with discrete spatiotemporal and kinematic parameters in low-disabled MS patients. METHOD: Thirty-four relapsing-remitting MS patients with an Expanded Disability Status Scale (EDSS) score ≤2 (mean age 36.32±8.72 years; 12 men, 22 women; mean EDSS 1.19±0.8) and twenty-two healthy controls (mean age 36.85±7.87 years; 6 men, 16 women) matched for age, weight, height, body mass index and gender underwent an instrumented gait analysis. RESULTS: No significant difference in GPS values and in spatiotemporal parameters was found between patients and controls. However patients showed a significant alteration at the ankle and pelvis level. CONCLUSION: GPS fails to identify gait abnormalities in low-disabled MS patients, although kinematic analysis revealed subtle gait alterations. Future studies should investigate other methods to assess gait impairments with a gait score in low-disabled MS patients.

Functional studies of the 5'-untranslated region of human 5-HT4 receptor mRNA.

The serotonin 5-HT4 receptor (where 5-HT stands for 5-hydroxy-tryptamine) is a member of the seven transmembrane-spanning G-protein-coupled family of receptors and mediates many cellular functions both in the central nervous system and at the periphery. In the present study, we isolated and characterized the 5'-flanking region of the h5-HT4 (human 5-HT4) receptor. We demonstrate the existence of a novel exon that corresponds to the 5'-untranslated region of the h5-HT4 receptor gene. RNase protection analysis and reverse transcriptase-PCR experiments performed on human atrial RNA demonstrated that the major transcription start site of the h5-HT4 receptor gene is located at -3185 bp relative to the first ATG codon. In addition, a 1.2 kb promoter fragment which drives the transcription of the 5-HT4 receptor was characterized. The promoter region lacks TATA and CAAT canonical motifs in the appropriate location, but contains putative binding sites for several transcription factors. Transient transfection assays revealed that the (-3299/-3050) gene fragment possesses the ability to promote the expression of the luciferase reporter gene in human cell lines. In contrast, the promoter was silent in monkey COS-7 cells, indicating the requirement of specific factors to initiate transcription in human cells. In addition to the promoter element, enhancer activity was found in a region (-220/-61) located in the long 5'-untranslated region. Mutational analysis, gel shift and transfection assays identified an Nkx2.5 (NK2-transcription-factor-related 5)-like binding site as a regulatory sequence of this enhancer. Our results suggest a complex regulation of the h5-HT4 receptor gene expression involving distinct promoters and non-coding exons.

Regulation of the amyloid precursor protein ectodomain shedding by the 5-HT4 receptor and Epac.

The serotonin 5-hydroxytryptamine (5-HT4) receptor is of potential interest for the treatment of Alzheimer's disease because it increases memory and learning. In this study, we investigated the effect of zinc metalloprotease inhibitors on the amyloid precursor protein (APP) processing induced by the serotonin 5-HT4 receptor in vitro. We show that secretion of the non-amyloidogenic form of APP, sAPPalpha induced by the 5-HT4(e) receptor isoform was not due to a general boost of the constitutive secretory pathway but rather to its specific effect on alpha-secretase activity. Although the h5-HT4(e) receptor increased IP3 production, inhibition of PKC did not modify its effect on sAPPalpha secretion. In addition, we found that alpha secretase activity is regulated by the cAMP-regulated guanine nucleotide exchange factor, Epac and the small GTPase Rac.