Locus Coeruleus and Noradrenergic Pharmacology in Neurodegenerative Disease

Adrenoceptors (ARs) throughout the brain are stimulated by noradrenaline originating mostly from neurons of the locus coeruleus, a brainstem nucleus that is ostensibly the earliest to show detectable pathology in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. The α₁-AR, α₂-AR, and β-AR subtypes expressed in target brain regions and on a range of cell populations define the physiological responses to noradrenaline, which includes activation of cognitive function in addition to modulation of neurometabolism, cerebral blood flow, and neuroinflammation. As these heterocellular functions are critical for maintaining brain homeostasis and neuronal health, combating the loss of noradrenergic tone from locus coeruleus degeneration may therefore be an effective treatment for both cognitive symptoms and disease modification in neurodegenerative indications. Two pharmacologic approaches are receiving attention in recent clinical studies: preserving noradrenaline levels (e.g., via reuptake inhibition) and direct activation of target adrenoceptors. Here, we review the expression and role of adrenoceptors in the brain, the preclinical studies which demonstrate that adrenergic stimulation can support cognitive function and cerebral health by reversing the effects of noradrenaline depletion, and the human data provided by pharmacoepidemiologic analyses and clinical trials which together identify adrenoceptors as promising targets for the treatment of neurodegenerative disease.

Detection of Clenbuterol-Induced Changes in Heart Rate Using At-Home Recorded Smartwatch Data: Randomized Controlled Trial

Background

Although electrocardiography is the gold standard for heart rate (HR) recording in clinical trials, the increasing availability of smartwatch-based HR monitors opens up possibilities for drug development studies. Smartwatches allow for inexpensive, unobtrusive, and continuous HR estimation for potential detection of treatment effects outside the clinic, during daily life.

Objective

The aim of this study is to evaluate the repeatability and sensitivity of smartwatch-based HR estimates collected during a randomized clinical trial.

Methods

The data were collected as part of a multiple-dose, investigator-blinded, randomized, placebo-controlled, parallel-group study of 12 patients with Parkinson disease. After a 6-day baseline period, 4 and 8 patients were treated for 7 days with an ascending dose of placebo and clenbuterol, respectively. Throughout the study, the smartwatch provided HR and sleep state estimates. The HR estimates were quantified as the 2.5th, 50th, and 97.5th percentiles within awake and asleep segments. Linear mixed models were used to calculate the following: (1) the intraclass correlation coefficient (ICC) of estimated sleep durations, (2) the ICC and minimum detectable effect (MDE) of the HR estimates, and (3) the effect sizes of the HR estimates.

Results

Sleep duration was moderately repeatable (ICC=0.64) and was not significantly affected by study day (P=.83), clenbuterol (P=.43), and study day by clenbuterol (P=.73). Clenbuterol-induced changes were detected in the asleep HR as of the first night (+3.79 beats per minute [bpm], P=.04) and in the awake HR as of the third day (+8.79 bpm, P=.001). The median HR while asleep had the highest repeatability (ICC=0.70). The MDE (N=12) was found to be smaller when patients were asleep (6.8 bpm to 11.7 bpm) than while awake (10.7 bpm to 22.1 bpm). Overall, the effect sizes for clenbuterol-induced changes were higher while asleep (0.49 to 2.75) than while awake (0.08 to 1.94).

Conclusions

We demonstrated the feasibility of using smartwatch-based HR estimates to detect clenbuterol-induced changes during clinical trials. The asleep HR estimates were most repeatable and sensitive to treatment effects. We conclude that smartwatch-based HR estimates obtained during daily living in a clinical trial can be used to detect and track treatment effects.

Trial Registration

Netherlands Trials Register NL8002; https://www.trialregister.nl/trial/8002

The shearing stress of baseball-spontaneous coronary artery dissection in a male athlete

The following is a case report of an atypical presentation of spontaneous coronary artery disease. In this case, a male with risk factors, precipitated by an emotional stress, presented to the emergency room with atypical chest pain. Cardiac catheterization revealed tapering of the mid-left anterior descending artery, consistent with non-atherosclerotic spontaneous coronary artery disease. However due to repeat chest pain, a repeat cardiac catheterization was performed, revealing 100% occlusion of the mid-LAD. This case represents an atypical presentation of a pathology that is frequently missed, and underreported. This is important to discuss in order to increase awareness, as the management and follow up are actually conservative.

Personalized healthcare: how to improve outcomes by increasing benefit and decreasing risk through the use of biomarkers

The use of personalized healthcare is beginning to show promise as a means of increasing benefit and decreasing risk for patients, but much work needs to be done in order to fully exploit the advances in medical science that have occurred over the last 30 years. In particular, molecular approaches that aim to characterize patient individuality must be combined with genetic approaches to capture the promise of this potential revolution in the practice of medicine.

Functional characterization of vasopressin type 2 receptor substitutions (R137H/C/L) leading to nephrogenic diabetes insipidus and nephrogenic syndrome of inappropriate antidiuresis: implications for treatments

Substitution of arginine-137 of the vasopressin type 2 receptor (V2R) for histidine (R137H-V2R) leads to nephrogenic diabetes insipidus (NDI), whereas substitution of the same residue to cysteine or leucine (R137C/L-V2R) causes the nephrogenic syndrome of inappropriate antidiuresis (NSIAD). These two diseases have opposite clinical outcomes. Still, the three mutant receptors were shown to share constitutive beta-arrestin recruitment and endocytosis, resistance to vasopressin-stimulated cAMP production and mitogen-activated protein kinase activation, and compromised cell surface targeting, raising questions about the contribution of these phenomenons to the diseases and their potential treatments. Blocking endocytosis exacerbated the elevated basal cAMP levels promoted by R137C/L-V2R but not the cAMP production elicited by R137H-V2R, demonstrating that substitution of Arg137 to Cys/Leu, but not His, leads to constitutive V2R-stimulated cAMP accumulation that most likely underlies NSIAD. The constitutively elevated endocytosis of R137C/L-V2R attenuates the signaling and most likely reduces the severity of NSIAD, whereas the elevated endocytosis of R137H-V2R probably contributes to NDI. The constitutive signaling of R137C/L-V2R was not inhibited by treatment with the V2R inverse agonist satavaptan (SR121463). In contrast, owing to its pharmacological chaperone property, SR121463 increased the R137C/L-V2R maturation and cell surface targeting, leading to a further increase in basal cAMP production, thus disqualifying it as a potential treatment for patients with R137C/L-V2R-induced NSIAD. However, vasopressin was found to promote beta-arrestin/AP-2-dependent internalization of R137H/C/L-V2R beyond their already elevated endocytosis levels, raising the possibility that vasopressin could have a therapeutic value for patients with R137C/L-V2R-induced NSIAD by reducing steady-state surface receptor levels, thus lowering basal cAMP production.

Engineered protein connectivity to actin mimics PDZ-dependent recycling of G protein-coupled receptors but not its regulation by Hrs

Many G protein-coupled receptors (GPCRs) recycle after agonist-induced endocytosis by a sequence-dependent mechanism, which is distinct from default membrane flow and remains poorly understood. Efficient recycling of the beta2-adrenergic receptor (beta2AR) requires a C-terminal PDZ (PSD-95/Discs Large/ZO-1) protein-binding determinant (PDZbd), an intact actin cytoskeleton, and is regulated by the endosomal protein Hrs (hepatocyte growth factor-regulated substrate). The PDZbd is thought to link receptors to actin through a series of protein interaction modules present in NHERF/EBP50 (Na+/H+ exchanger 3 regulatory factor/ezrin-binding phosphoprotein of 50 kDa) family and ERM (ezrin/radixin/moesin) family proteins. It is not known, however, if such actin connectivity is sufficient to recapitulate the natural features of sequence-dependent recycling. We addressed this question using a receptor fusion approach based on the sufficiency of the PDZbd to promote recycling when fused to a distinct GPCR, the delta-opioid receptor, which normally recycles inefficiently in HEK293 cells. Modular domains mediating actin connectivity promoted receptor recycling with similarly high efficiency as the PDZbd itself, and recycling promoted by all of the domains was actin-dependent. Regulation of receptor recycling by Hrs, however, was conferred only by the PDZbd and not by downstream interaction modules. These results suggest that actin connectivity is sufficient to mimic the core recycling activity of a GPCR-linked PDZbd but not its cellular regulation.

Aripiprazole has functionally selective actions at dopamine D2 receptor-mediated signaling pathways

Aripiprazole is a unique atypical antipsychotic drug with an excellent side-effect profile presumed, in part, to be due to lack of typical D(2) dopamine receptor antagonist properties. Whether aripiprazole is a typical D(2) partial agonist, or a functionally selective D(2) ligand, remains controversial (eg D(2)-mediated inhibition of adenylate cyclase is system dependent; aripiprazole antagonizes D(2) receptor-mediated G-protein-coupled inwardly rectifying potassium channels and guanosine triphosphate nucleotide (GTP)gammaS coupling). The current study examined the D(2L) receptor binding properties of aripiprazole, as well as the effects of the drug on three downstream D(2) receptor-mediated functional effectors: mitogen-activated protein kinase (MAPK) phosphorylation, potentiation of arachidonic acid (AA) release, and D(2) receptor internalization. Unlike quinpirole (a full D(2) agonist) or (-)3PPP (S(-)-3-(3-hydroxyphenyl)-N-propylpiperidine hydrochloride, a D(2) partial agonist), the apparent D(2) affinity of aripiprazole was not decreased significantly by GTP. Moreover, full or partial agonists are expected to have Hill slopes <1.0, yet that of aripiprazole was significantly >1.0. Whereas aripiprazole partially activated both the MAPK and AA pathways, its potency vs MAPK phosphorylation was much lower relative to potencies in assays either of AA release or inhibition of cyclic adenosine 3',5'-cyclic monophosphate accumulation. In addition, unlike typical agonists, neither aripiprazole nor (-)3PPP produced significant internalization of the D(2L) receptor. These data are clear evidence that aripiprazole affects D(2L)-mediated signaling pathways in a differential manner. The results are consistent with the hypothesis that aripiprazole is a functionally selective D(2) ligand rather than a simple partial agonist. Such data may be useful in understanding the novel clinical actions of this drug.

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD): a paradigm for activating mutations causing endocrine dysfunction

Mutations of G protein-coupled receptors are responsible for a wide range of diseases. With respect to water balance and vasopressin signaling, more than 180 different inactivating mutations have been previously described in the V2 vasopressin receptor (V2R), resulting in nephrogenic diabetes insipidus. In contrast, we have recently described the first known patients with V2R activating mutations. Patients with these novel gain-of-function V2R mutations have a disorder which we have termed "nephrogenic syndrome of inappropriate antidiuresis" (NSIAD): a clinical presentation consistent with the syndrome of inappropriate antidiuretic hormone secretion but with undetectable levels of arginine vasopressin (antidiuretic hormone). The mechanisms by which these mutations constitutively activate the V2R are currently being investigated.

Nephrogenic syndrome of inappropriate antidiuresis

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a common cause of hyponatremia. We describe two infants whose clinical and laboratory evaluations were consistent with the presence of SIADH, yet who had undetectable arginine vasopressin (AVP) levels. We hypothesized that they had gain-of-function mutations in the V2 vasopressin receptor (V2R). DNA sequencing of each patient's V2R gene (AVPR2) identified missense mutations in both, with resultant changes in codon 137 from arginine to cysteine or leucine. These novel mutations cause constitutive activation of the receptor and are the likely cause of the patients' SIADH-like clinical picture, which we have termed "nephrogenic syndrome of inappropriate antidiuresis."

Peri/nuclear localization of intact insulin-like growth factor binding protein-2 and a distinct carboxyl-terminal IGFBP-2 fragment in vivo

Insulin-like growth factor binding protein-2 (IGFBP-2) as one of the most important IGFBPs has never been assessed in the intracellular compartment in vivo. Since there is evidence for novel intracellular functions of distinct IGFBPs, we investigated the presence of IGFBP-2 inside the cell. In peri/nuclear fractions of various tissues isolated from IGFBP-2 transgenic and non-transgenic mice we were able to show the presence of intact IGFBP-2. In addition, we demonstrate the presence of a highly conserved carboxyl-terminal IGFBP-2 fragment in the peri/nuclear fraction by using different peptide-induced antibodies. In pancreatic sections, confocal microscopy revealed the presence of IGFBP-2 on the nuclear surface but not within the nucleus. Our findings suggest novel functions of intact IGFBP-2 and IGFBP-2 fragments within the cell.

Identification of a novel endocytic recycling signal in the D1 dopamine receptor

A critical event determining the functional consequences of G protein-coupled receptor (GPCR) endocytosis is the molecular sorting of internalized receptors between divergent recycling and degradative membrane pathways. The D1 dopamine receptor recycles rapidly and efficiently to the plasma membrane after agonist-induced endocytosis and is remarkably resistant to proteolytic down-regulation. Whereas the mechanism mediating agonist-induced endocytosis of D1 receptors has been investigated in some detail, little is known about how receptors are sorted after endocytosis. We have identified a sequence present in the carboxyl-terminal cytoplasmic domain of the human D1 dopamine receptor that is specifically required for the efficient recycling of endocytosed receptors back to the plasma membrane. This sequence is distinct from previously identified membrane trafficking signals and is located in a proximal portion of the carboxyl-terminal cytoplasmic domain, in contrast to previously identified GPCR recycling signals present at the distal tip. Nevertheless, fusion of this sequence to the carboxyl terminus of a chimeric mutant delta opioid neuropeptide receptor is sufficient to re-route internalized receptors from lysosomal to recycling membrane pathways, defining this sequence as a bona fide endocytic recycling signal that can function in both proximal and distal locations. These results identify a novel sorting signal controlling the endocytic trafficking itinerary of a physiologically important dopamine receptor, provide the first example of such a sorting signal functioning in a proximal portion of the carboxyl-terminal cytoplasmic domain, and suggest the existence of a diverse array of sorting signals in the GPCR superfamily that mediate subtype-specific regulation of receptors via endocytic membrane trafficking.

Mutation of the RGD sequence does not affect plasma membrane association and growth inhibitory effects of elevated IGFBP-2 in vivo

Using insulin-like growth factor-binding protein-2 (IGFBP-2) transgenic mice (D mice) as a model of elevated IGFBP-2 expression, which is often found in unphysiological conditions, we found association of IGFBP-2 to purified plasma membranes of many organs. To determine whether the RGD (Arg-Gly-Asp) motif of IGFBP-2 mediates cell surface binding in vivo, we mutated the RGD motif of IGFBP-2 into an RGE (Arg-Gly-Glu) sequence and produced transgenic mice (E mice) which express elevated amounts of mutated IGFBP-2. Our data demonstrate that in vivo IGFBP-2 cell surface association is not dependent on the RGD motif and that mutation of this sequence does not alter growth inhibitory effects of IGFBP-2.

Hepatocyte growth factor in renal failure: promise and reality

Can science discover some secrets of Greek mythology? In the case of Prometheus, we can now suppose that his amazing hepatic regeneration was caused by a peptide growth factor called hepatocyte growth factor (HGF). Increasing evidence indicates that HGF acts as a multifunctional cytokine on different cell types. This review addresses the molecular mechanisms that are responsible for the pleiotropic effects of HGF. HGF binds with high affinity to its specific tyrosine kinase receptor c-met, thereby stimulating not only cell proliferation and differentiation, but also cell migration and tumorigenesis. The three fundamental principles of medicine-prevention, diagnosis, and therapy-may be benefited by the rational use of HGF. In renal tubular cells, HGF induces mitogenic and morphogenetic responses. In animal models of toxic or ischemic acute renal failure, HGF acts in a renotropic and nephroprotective manner. HGF expression is rapidly up-regulated in the remnant kidney of nephrectomized rats, inducing compensatory growth. In a mouse model of chronic renal disease, HGF inhibits the progression of tubulointerstitial fibrosis and kidney dysfunction. Increased HGF mRNA transcripts were detected in mesenchymal and tubular epithelial cells of rejecting kidney. In transplanted patients, elevated HGF levels may indicate renal rejection. When HGF is considered as a therapeutic agent in human medicine, for example, to stimulate kidney regeneration after acute injury, strategies need to be developed to stimulate cell regeneration and differentiation without an induction of tumorigenesis.

CCG1/TAF(II)250 regulates epidermal growth factor receptor gene transcription in cell cycle mutant ts13

The epidermal growth factor receptor (EGFR) plays a critical role in normal growth and its overexpression is associated with several types of cancer. To learn more about regulation of the expression of this important receptor, we investigated the role of the TAF(II)250 subunit of transcription factor IID in the transcription of the EGFR gene. The EGFR gene has a TATA-less promoter and TAF(II)250 has previously been shown to have an important regulatory role in such promoters. The study was performed in the ts13 hamster cell line which has a temperature-sensitive mutation in the CCG1 gene that encodes TAF(II)250. At the nonpermissive temperature, the transcription of a few cell cycle-dependent genes is depressed in ts13 cells while global RNA synthesis is unaffected. Using this model system, we found that EGFR promoter-driven luciferase expression in transiently transfected ts13 cells decreased 8, 25, and 50-fold after 12, 24, and 48 hours, respectively, at the nonpermissive temperature. The decrease was partially rescued by cotransfection with the wild-type CCG1 gene. The expression of endogenous EGFR also appeared to be regulated by TAF(II)250--the maximum binding capacity of ts13 cells for 125I-labeled EGF decreased approximately twofold when incubated for 2 days at the nonpermissive temperature. Placing these studies in the context of the current understanding of the TFIID transcription complex, we speculate that selective stimulation of EGFR gene transcription may be mediated by TAF(II)250 interaction with enhancer-bound activators and the basal transcription machinery.

Reduced epidermal growth factor receptor expression in hypohidrotic ectodermal dysplasia and Tabby mice

Patients with hypohidrotic ectodermal dysplasia (HED) and Tabby (Ta) mice lack sweat glands and there is compelling evidence that these phenotypes are caused by mutations in the same highly conserved but unidentified X-linked gene. Previous studies showed that exogenous epidermal growth factor (EGF) reversed the Ta phenotype but the EGF status in HED patients has not been studied at all. Studies reported herein investigated the hypothesis that the EGF signaling pathway is involved in HED/Ta. Fibroblasts from HED patients had a two- to eightfold decrease in binding capacity for (125)I-labeled EGF, a decreased expression of the immunoreactive 170-kD EGF receptor (EGFR) protein, and a corresponding reduction in EGFR mRNA. Reduced expression of the EGFR also was observed in Ta fibroblasts and liver membranes. Other aspects of the EGF signaling pathway, including EGF concentration in urine and plasma, were normal in both HED patients and Ta mice. We propose that a decreased expression of the EGFR plays a causal role in the HED/Ta phenotype.