Adiponectin receptor signalling in the brain

Impact of the ADHD-susceptibility gene CDH13 on development and function of brain networks

Attention-deficit/hyperactivity disorder (ADHD) is a common, early onset and enduring neuropsychiatric disorder characterized by developmentally inappropriate inattention, hyperactivity, increased impulsivity and motivational/emotional dysregulation with similar prevalence rates throughout different cultural settings. Persistence of ADHD into adulthood is associated with considerable risk for co-morbidities such as depression and substance use disorder. Although the substantial heritability of ADHD is well documented the etiology is characterized by a complex coherence of genetic and environmental factors rendering identification of risk genes difficult. Genome-wide linkage as well as single nucleotide polymorphism (SNP) and copy-number variant (CNV) association scans recently allow to reliably define aetiopathogenesis-related genes. A considerable number of novel ADHD risk genes implicate biological processes involved in neurite outgrowth and axon guidance. Here, we focus on the gene encoding Cadherin-13 (CDH13), a cell adhesion molecule which was replicably associated with liability to ADHD and related neuropsychiatric conditions. Based on its unique expression pattern in the brain, we discuss the molecular structure and neuronal mechanisms of Cadherin-13 in relation to other cadherins and the cardiovascular system. An appraisal of various Cadherin-13-modulated signaling pathways impacting proliferation, migration and connectivity of specific neurons is also provided. Finally, we develop an integrative hypothesis of the mechanisms in which Cadherin-13 plays a central role in the regulation of brain network development, plasticity and function. The review concludes with emerging concepts about alterations in Cadherin-13 signaling contributing to the pathophysiology of neurodevelopmental disorders.

Adiponectin increases secretion of rat submandibular gland via adiponectin receptors-mediated AMPK signaling

Adiponectin and adiponectin receptors (AdipoR1/2) are expressed in various tissues and are involved in the regulation of multiple functions such as energy metabolism and inflammatory responses. However, the effect of adiponectin and AdipoRs in submandibular glands has not been fully evaluated. In the present study, we found that mRNA and protein of both adiponectin and AdipoR1/2 were expressed in rat submandibular glands and in the SMG-C6 cell line, as evidenced by RT-PCR and Western blot analysis. Immunofluorescence staining showed that adiponectin was diffused in the cytoplasm, while AdipoR1/2 was concentrated in the membrane of acinar cells. Saliva flow was significantly increased by full length adiponectin (fAd) or globular adiponectin (gAd) perfusion in isolated rat submandibular glands. 5-Aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR), an adenosine monophosphate activated protein kinase (AMPK) activator, also increased saliva secretion. fAd, gAd, and AICAR all increased the average width of apical tight junctions in perfused submandibular glands, and decreased transepithelial electrical resistance (TER) in SMG-C6 cells, suggesting that adiponectin promoted secretion by modulating paracellular permeability. fAd and gAd increased p-AMPK levels, while AraA, an AMPK antagonist, abolished fAd- and gAd-induced changes in secretion, tight junction ultrastructure, and TER. Moreover, both AdipoR1 and AdipoR2 were required for fAd- or gAd-induced p-AMPK and TER responses, suggesting from their inhibition following AdipoR1 or AdipoR2 knockdown, and co-knockdown of AdipoRs by RNA interference. Our results suggest that adiponectin functions as a promoter of salivary secretion in rat submandibular glands via activation of AdipoRs, AMPK, and paracellular permeability.

Ictal adiponectin levels in episodic migraineurs: a randomized pilot trial

OBJECTIVE

To assess ictal adiponectin (ADP) levels before and after acute abortive treatment in women episodic migraineurs.

METHODS

Peripheral blood specimens were collected from women episodic migraineurs before and after acute abortive treatment with sumatriptan/naproxen sodium vs placebo. Univariate and multivariate models were utilized to examine the relationship between serum total ADP (T-ADP), ADP oligomers (high molecular weight [HMW], middle molecular weight, and low molecular weight [LMW]-ADP), and ADP ratio levels and pain severity. Paired t-tests and random intercept longitudinal models were utilized to assess the mean changes in T-ADP, ADP oligomers, and ratios over time in treatment responders and nonresponders.

RESULTS

Twenty participants (11 responders, 9 nonresponders) have been studied to date. In all participants, increases in the HMW : LMW ADP ratio were associated with an increase in pain severity. For every 1 point increase in the HMW : LMW ratio, pain severity increased by 0.22 (Confidence Interval [CI]: 0.07, 0.37; P = .004). In contrast, for every 0.25 μg/mL increase in LMW-ADP, pain severity decreased by 0.20 (CI: -0.41, -0.002; P = .047). In treatment responders, T-ADP levels were reduced at 30 minutes (12.52 ± 3.4; P = .03), 60 minutes (12.32 ± 3.2; P = .017), and 120 minutes (12.65 ± 3.2; P = .016) after treatment as compared with onset (13.48 ± 3.8). Additionally, in responders, the HMW : LMW ratio level was greater at pain onset (3.70 ± 1.9 μg/mL) as compared with nonresponders (2.29 ± 0.71 μg/mL), P = .050. Responders also showed a decrease in the HMW : LMW ratio at 60 minutes (2.37 ± 1.1; P = .002) and 120 minutes (2.76 ± 1.4; P = .02) after treatment as compared with onset (3.70 ± 1.9). These changes in responders remained significant after adjusting for covariates, including measured body mass index (m-BMI). Although nonresponders showed no significant changes in unadjusted T-ADP or ADP oligomer or ratio levels, the HMW : LMW ratio was increased in nonresponders after adjustments (P = .025).

CONCLUSION

In this pilot study of women episodic migraineurs, the HMW : LMW ADP ratio level was associated with migraine severity and predictive of acute treatment response. ADP and the HMW : LMW ratio of ADP represent potential novel biomarkers and drug targets for episodic migraine.

Exercise and obesity in fibromyalgia: beneficial roles of IGF-1 and resistin?

Introduction

Severe fatigue is a major health problem in fibromyalgia (FM). Obesity is common in FM, but the influence of adipokines and growth factors is not clear. The aim was to examine effects of exercise on fatigue, in lean, overweight and obese FM patients.

Methods

In a longitudinal study, 48 FM patients (median 52 years) exercised for 15 weeks. Nine patients were lean (body mass index, BMI 18.5 to 24.9), 26 overweight (BMI 25 to 29.9) and 13 obese. Fatigue was rated on a 0 to 100 mm scale (fibromyalgia impact questionnaire [FIQ] fatigue) and multidimensional fatigue inventory (MFI-20) general fatigue (MFIGF). Higher levels in FIQ fatigue and MFIGF indicate greater degree of fatigue. Free and total IGF-1, neuropeptides, adipokines were determined in serum and cerebrospinal fluid (CSF).

Results

Baseline FIQ fatigue correlated negatively with serum leptin (r = -0.345; P = 0.016) and nerve growth factor (NGF; r = -0.412; P = 0.037). In lean patients, baseline MFIGF associated negatively with serum resistin (r = -0.694; P = 0.038). FIQ Fatigue associated negatively with CSF resistin (r = -0.365; P = 0.073). Similarly, FIQ fatigue (r = -0.444; P = 0.026) and MFIGF correlated negatively with CSF adiponectin (r = -0.508; P = 0.01). In lean patients, FIQ fatigue (P = 0.046) decreased after 15 weeks. After 30 weeks, MFIGF decreased significantly in lean (MFIGF: P = 0.017), overweight (MFIGF: P = 0.001), and obese patients (MFIGF: P = 0.016). After 15 weeks, total IGF-1 increased in lean (P = 0.043) patients. ∆Total IGF-1 differed significantly between lean and obese patients (P = 0.010). ∆Total IGF-1 related negatively with ∆MFIGF after 15 weeks (r = -0.329; P = 0.050). After 30 weeks, ∆FIQ fatigue negatively correlated with ∆NGF (r = -0.463; P = 0.034) and positively with ∆neuropeptide Y (NPY) (r = 0.469; P = 0.032). Resistin increased after 30 weeks (P = 0.034). ∆MFIGF correlated negatively with ∆resistin (r = -0.346; P = 0.031), being strongest in obese patients (r = -0.815; P = 0.007). In obese patients, ∆FIQ fatigue after 30 weeks correlated negatively with ∆free IGF-1 (r = -0.711; P = 0.032).

Conclusions

Exercise reduced fatigue in all FM patients, this effect was achieved earlier in lean patients. Baseline levels of resistin in both serum and CSF associated negatively with fatigue. Resistin was increased after the exercise period which correlated with decreased fatigue. Changes in IGF-1 indicate similar long-term effects in obese patients. This study shows reduced fatigue after moderate exercise in FM and indicates the involvement of IGF-1 and resistin in these beneficial effects.

Trial registration

ClinicalTrials.gov: NCT00643006

Pivotal roles of monocytes/macrophages in stroke

Stroke is an important issue in public health due to its high rates both of morbidity and mortality, and high rate of disability. Hypertension, cardiovascular disease, arterial fibrillation, diabetes mellitus, smoking, and alcohol abuse are all risk factors for stroke. Clinical observations suggest that inflammation is also a direct risk factor for stroke. Patients with stroke have high levels of inflammatory cytokines in plasma, and immune cells, such as macrophages and T-lymphocytes, are noted within stroke lesions. These inflammatory events are considered as a result of stroke. However, recent studies show that plasma levels of inflammatory cytokines or soluble adhesion molecules are high in patients without stroke, and anti-inflammatory therapy is effective at reducing stroke incidence in not only animal models, but in humans as well. Statins have been shown to decrease the stroke incidence via anti-inflammatory effects that are both dependent and independent of their cholesterol-lowering effects. These reports suggest that inflammation might directly affect the onset of stroke. Microglial cells and blood-derived monocytes/macrophages play important roles in inflammation in both onset and aggravation of stroke lesions. We review the recent findings regarding the role of monocytes/macrophages in stroke.

Molecules affecting hypothalamic control of core body temperature in response to calorie intake

Core body temperature (CBT) and calorie intake are main components of energy homeostasis and two important regulators of health, longevity, and aging. In homeotherms, CBT can be influenced by calorie intake as food deprivation or calorie restriction (CR) lowers CBT whereas feeding has hyperthermic effects. The finding that in mice CBT prolonged lifespan independently of CR, suggested that the mechanisms modulating CBT may represent important regulators of aging. Here we summarize the current knowledge on the signaling molecules and their receptors that participate in the regulation of CBT responses to calorie intake. These include hypothalamic neuropeptides regulating feeding but also energy expenditure via modulation of thermogenesis. We also report studies indicating that nutrient signals can contribute to regulation of CBT by direct action on hypothalamic preoptic warm-sensitive neurons that in turn regulate adaptive thermogenesis and hence CBT. Finally, we show the role played by two orphans G protein-coupled receptor: GPR50 and GPR83, that were recently demonstrated to regulate temperature-dependent energy expenditure.

Adiponectin: a biomarker for rheumatoid arthritis?

Recent achievements in the biology and the function of adipose tissue have regarded white adipose tissue (WAT) as an important endocrine and secretory organ. Releasing a series of multiple-function mediators, WAT is involved in a wide spectrum of diseases, including not only cardiovascular and metabolic complications, such as atherosclerosis and type 2 diabetes, but also inflammatory- and immune-related disorders, such as rheumatoid arthritis (RA) and osteoarthritis (OA). A large number of these mediators, called adipokines, such as tumor necrosis factor alpha (TNF-α), leptin, adiponectin, resistin, chemerin, interleukin-6 (IL-6), visfatin, and so on have been identified and studied widely. Important advances related to these proteins shed new insights into the pathophysiological mechanisms of many complicated diseases, although details of which remain unclear. Adiponectin, one of the most widely investigated adipokine, has been shown to possess both anti- and pro-inflammatory effects. RA is a chronic systemic inflammatory-related autoimmune disease. Accumulated evidence has demonstrated that cytokines and adipokines play an important role in the pathogenesis of RA. In this review, we have summarized the most recent advances in adiponectin research in the context of RA, focusing primarily on its effect on RA-related cells, its regulation on pro-inflammatory cytokines, as well as its validation as a biomarker for RA.

Is secretoneurin a new hormone?

Numerous small potentially bioactive peptides are derived from the selective processing of the ~600 amino acid secretogranin II (SgII) precursor, but only the 31-42 amino acid segment termed secretoneurin (SN) is well-conserved from sharks to mammals. Both SNa and SNb paralogs have been identified in some teleosts, likely arising as a result of the specific genome duplication event in this lineage. Only one copy of the putative lamprey SgII (188 amino acids) could be identified which gives rise to a divergent agnathan SN that contains the signature YTPQ-X-LA-X(7)-EL sequence typical of the central core of all known SN peptides. In rodent models, SN has regulatory effects on neuroinflammation and neurotransmitter release, and possesses therapeutic potential for the induction of angiogenesis. The wide distribution of SN in neuroendocrine neurons and pituitary cells suggests important endocrine roles. The clearest example of the endocrine action of SN is the stimulatory effects on pituitary luteinizing hormone release from goldfish pituitary and mouse LβT2 gonadotroph cells, indicative of an important role in reproduction. Several lines of evidence suggest that the SN receptor is most likely a G-protein coupled protein. Microarray analysis of SN effects on dispersed goldfish pituitary cells in vitro reveals novel SN actions that include effects on genes involved in notch signaling and the guanylate cyclase pathway. Intracerebroventricular injection of SN increases feeding and locomotory behaviors in goldfish. Given that SgII appeared early in vertebrate evolution, SN is an old peptide with emerging implications as a new multifunctional hormone.

AdipoR1 and 2 are expressed on warm sensitive neurons of the hypothalamic preoptic area and contribute to central hyperthermic effects of adiponectin

Adiponectin can act in the brain to increase energy expenditure and reduce body weight by mechanisms not entirely understood. We found that adiponectin type 1 and type 2 receptors (AdipoR1 and AdipoR2) are expressed in warm sensitive neurons of the hypothalamic preoptic area (POA) which play a critical role in the regulation of core body temperature (CBT) and energy balance. Thus, we tested the ability of adiponectin to influence CBT in wild-type mice and in mice deficient for AdipoR1 or AdipoR2. Local injection of adiponectin into the POA induced prolonged elevation of core body temperature and decreased respiratory exchange ratio (RER) indicating that increased energy expenditure is associated with increased oxidation of fat over carbohydrates. In AdipoR1 deficient mice, the ability of adiponectin to raise CBT was significantly blunted and its ability to decrease RER was completely lost. In AdipoR2 deficient mice, adiponectin had only diminished hyperthermic effects but reduced RER similarly to wild type mice. These results indicate that adiponectin can contribute to energy homeostasis by regulating CBT by direct actions on AdipoR1 and R2 in the POA.