Diverse distribution of tyrosine receptor kinase B isoforms in rat multiple tissues

TrkB phosphorylation in serum extracellular vesicles correlates with cognitive function enhanced by ergothioneine in humans

Oral administration of the food-derived antioxidant amino acid ergothioneine (ERGO) results in its efficient distribution in the brain and enhances cognitive function. However, effect of ERGO deficiency on cognitive impairment and the underlying mechanisms remain unknown. We revealed that cognitive function and hippocampal neurogenesis were lower in mice fed an ERGO-free diet than in those fed the control diet. Furthermore, ERGO supplementation to achieve the control diet ERGO levels reversed these effects and restored ERGO concentrations in the plasma and hippocampus. The ERGO-induced recovery of cognitive function and hippocampal neurogenesis was blocked by inhibiting the neurotrophic factor receptor tropomyosin receptor kinase B (TrkB), with a concomitant reduction in hippocampal phosphorylated TrkB, suggesting the involvement of TrkB in these events in mice. Phosphorylated TrkB was also detected in extracellular vesicles (EVs) derived from serum of volunteers who had been orally administered placebo or ERGO-containing tablets. Importantly, the ratio of serum EV-derived phosphorylated TrkB was significantly higher in the ERGO-treated group than in the placebo-treated group and was positively correlated with both serum ERGO concentrations and several cognitive domain scores from Cognitrax. Altogether, TrkB phosphorylation is involved in ERGO-induced cognitive enhancement in mice, and TrkB phosphorylation levels in serum EVs may quantitatively represent ERGO-induced cognitive enhancement in humans.

Autocrine role of senescent cardiac fibroblasts-derived extracellular vesicles

Cellular senescence is a highly stable state associated with cell cycle arrest, that is elicited in response to various stresses. The accumulation of senescent cells in tissues drives age-related diseases. Recent studies have shown that the cellular senescence enhances an extracellular vesicles (EV) secretion. EV are lipid-bilayer-capsuled particles released by various cells mediating cell-to-cell communication. It was recently reported that EV secreted by the senescent cells had several functions such as cancer cell proliferation and immune cell activation. In the present study, we investigated whether senescent cardiac fibroblasts-derived EV play an autocrine/paracrine role in the heart cells. Neonatal rat cardiac fibroblasts (NRCFs) were treated with doxorubicin (DOX) to induce cellular senescence. EV were isolated from NRCFs culture media. The vehicle-treated NRCFs-derived EV (D0-EV, 72 hr) increased a living cell number in NRCFs, which was attenuated by DOX (1,000 nM)-treated NRCFs-derived EV (D103-EV, 72 hr). While D0-EV did not affect protein concentration in NRCFs, D103-EV decreased it. Furthermore, D103-EV significantly increased a ratio of microtubule-associated protein 1 light chain 3 (LC3)-II to LC3-I in NRCFs, indicating an induction of autophagy. In addition, D103-EV increased phosphorylation of adenosine monophosphate-activated kinase (AMPK) α in NRCFs. In neonatal rat cardiomyocytes, however, NRCFs-derived EV (72 hr) had no effect on the living cell number, protein concentration, and ratio of LC3-II to LC3-I. In conclusion, we for the first time revealed that DOX-induced senescent NRCFs-derived EV induce autophagy in NRCFs perhaps partly through the activation of AMPKα.

Is Brain-Derived Neurotrophic Factor a Metabolic Hormone in Peripheral Tissues?

Simple Summary

The activity of brain-derived neurotrophic factor (BDF) in the central nervous system has been well-studied, but its physiological role in other organs has not been clearly defined. This review summarizes the current findings on the functionality of BDNF in various peripheral tissues and discusses several unresolved questions in the field.

Abstract

Brain-derived neurotrophic factor (BDNF) is an important growth factor in the central nervous system. In addition to its well-known activities in promoting neuronal survival, neuron differentiation, and synaptic plasticity, neuronal BDNF also regulates energy homeostasis by modulating the hypothalamus’s hormonal signals. In the past decades, several peripheral tissues, including liver, skeletal muscle, and white adipose tissue, were demonstrated as the active sources of BDNF synthesis in response to different metabolic challenges. Nevertheless, the functions of BDNF in these tissues remain obscure. With the use of tissue-specific Bdnf knockout animals and the availability of non-peptidyl BDNF mimetic, increasing evidence has reported that peripheral tissues-derived BDNF might play a significant role in maintaining systemic metabolism, possibly through the regulation of mitochondrial dynamics in the various tissues. This article reviews the autocrine/paracrine/endocrine functions of BDNF in non-neuronal tissues and discusses the unresolved questions about BDNF’s function.

The Ketogenic Diet Improves Gut-Brain Axis in a Rat Model of Irritable Bowel Syndrome: Impact on 5-HT and BDNF Systems

Altered gut-brain communication can contribute to intestinal dysfunctions in the intestinal bowel syndrome. The neuroprotective high-fat, adequate-protein, low-carbohydrate ketogenic diet (KD) modulates the levels of different neurotransmitters and neurotrophins. The aim was to evaluate the effects of KD on levels of 5-HT, the receptors 5-HT_3B and 5-HT₄, the 5-HT transporter SERT, the neurotrophin BDNF, and its receptor TrkB in the colon and brain of a rat model of irritable bowel syndrome (IBS). Samples from Wistar rats exposed to maternal deprivation as newborns and then fed with a standard diet (IBS-Std) or KD (IBS-KD) for ten weeks were analyzed. As controls, unexposed rats (Ctrl-Std and Ctrl-KD) were studied. IBS-Std rats had a disordered enteric serotoninergic signaling shown by increased mucosal 5-HT content and reduced SERT, 5-HT_3B, and 5-HT₄ levels compared to controls. In the brain, these animals showed up-regulation of the BDNF receptor TrkB as a counteracting response to the stress-induced reduction of the neurotrophin. KD showed a dual effect in improving the altered 5-HT and BDNF systems. It down-regulated the increased mucosal 5-HT without affecting transporter and receptor levels. KD improved brain BDNF levels and established negative feedback, leading to a compensatory downregulation of TrkB to maintain a physiological steady state.

Feeding and food availability modulate brain-derived neurotrophic factor, an orexigen with metabolic roles in zebrafish

Emerging findings point to a role for brain-derived neurotrophic factor (BDNF) on feeding in mammals. However, its role on energy balance is unclear. Moreover, whether BDNF regulates energy homeostasis in non-mammals remain unknown. This research aimed to determine whether BDNF is a metabolic peptide in zebrafish. Our results demonstrate that BDNF mRNAs and protein, as well as mRNAs encoding its receptors trkb2, p75ntra and p75ntrb, are detectable in the zebrafish brain, foregut and liver. Intraperitoneal injection of BDNF increased food intake at 1, 2 and 6 h post-administration, and caused an upregulation of brain npy, agrp and orexin, foregut ghrelin, and hepatic leptin mRNAs, and a reduction in brain nucb2. Fasting for 7 days increased bdnf and p75ntrb mRNAs in the foregut, while decreased bdnf, trkb2, p75ntra and p75ntrb mRNAs in the brain and liver. Additionally, the expression of bdnf and its receptors increased preprandially, and decreased after a meal in the foregut and liver. Finally, we observed BDNF-induced changes in the expression and/or activity of enzymes involved in glucose and lipid metabolism in the liver. Overall, present results indicate that BDNF is a novel regulator of appetite and metabolism in fish, which is modulated by energy intake and food availability.

Acute intracerebroventricular injection of chemerin-9 increases systemic blood pressure through activating sympathetic nerves via CMKLR1 in brain

Chemerin is an adipocytokine involved in inflammation and lipid metabolism via G protein-coupled receptor, chemokine-like receptor (CMKLR)1. Since the important nuclei regulating pressure (BP) exist in the brain, we examined the effects of acute intracerebroventricular (i.c.v.) injection of chemerin-9 on systemic BP and explored underlying mechanisms. We examined the effects of acute i.c.v. injection of chemerin-9 (10 nmol/head) on systemic BP by a carotid cannulation method in the control or CMKLR1 small interfering (si) RNA-treated Wistar rats (0.04 nmol, 3 days, i.c.v.). We examined protein expression of CMKLR1 around brain ventricles by Western blotting. We examined the effects of acute i.c.v. injection of chemerin-9 on serum adrenaline by a high performance liquid chromatography. In the control siRNA-treated rats, chemerin-9 significantly increased mean BP, which reached a peak at 2 to 4 min after injection. On the other hand, in the CMKLR1 siRNA-treated rats, chemerin-9 did not affect the mean BP. Protein expression of CMKLR1 specifically in subfornical organ (SFO) and paraventricular nucleus (PVN) from the CMKLR1 siRNA-treated rats decreased compared with the control siRNA-treated rats. In the control siRNA-treated rats, chemerin-9 increased serum adrenaline level. On the other hand, in the CMKLR1 siRNA-treated rats, chemerin-9 did not affect the serum adrenaline level. Further, pretreatment with prazosin, an α-adrenaline receptor blocker, significantly prevented the pressor responses induced by chemerin-9. In summary, we for the first time demonstrated that chemerin-9 stimulates the sympathetic nerves via CMKLR1 perhaps expressed in SFO and PVN, which leads to an increase in systemic BP.

Lactobacillus Rhamnosus GG Affects the BDNF System in Brain Samples of Wistar Rats with Pepsin-Trypsin-Digested Gliadin (PTG)-Induced Enteropathy

Celiac disease (CD) presents as chronic low-grade inflammation of the small intestine often characterized by psychiatric comorbidities. The brain-derived neurotrophic factor (BDNF), which we have shown to be reduced in the serum of CD patients, acts as the bridge between immune activation and the nervous system adaptive response. Since Lactobacillus has been shown to upregulate BDNF, this study aimed to evaluate whether the administration of Lactobacillus rhamnosus GG (L.GG) could positively affect the brain BDNF system in rats mimicking the CD lesions. Data have shown that the administration of pepsin-trypsin digested gliadin (PTG) and L.GG alter the levels of mature BDNF (mBDNF), as evaluated by Western blotting. PTG provoked a reduction of mBDNF compared to controls, and a compensatory increase of its receptor TrkB. L.GG induced a slight positive effect on mBDNF levels under normal conditions, while it was able to rescue the PTG-induced reduced expression of mBDNF. The curative effect of L.GG was finely tuned, accompanied by the reduction of TrkB, probably to avoid the effect of excessive BDNF.

Canstatin suppresses isoproterenol-induced cardiac hypertrophy through inhibition of calcineurin/nuclear factor of activated T-cells pathway in rats

Pathological cardiac hypertrophy associated with cardiac dysfunction is an independent risk factor for arrhythmia, myocardial infarction and sudden death. Canstatin, a C-terminal fragment of type IV collagen α2 chain, is abundantly expressed in normal heart tissue. We previously demonstrated that canstatin inhibits isoproterenol (ISO)-induced dephosphorylation of nuclear factor of activated T-cells (NFAT)c4, which plays an important role in cardiac hypertrophy, in differentiated H9c2 cardiomyoblasts. Thus, we investigated whether in vivo canstatin administration prevents ISO-induced cardiac hypertrophy through the inhibition of NFATc4 pathway. Rats were subcutaneously injected with ISO (5 mg/kg) or saline (Cont) for 7 days. Simultaneously, recombinant mouse canstatin (20 μg/kg) or vehicle was intraperitoneally administered. After left ventricular wall thickness and cardiac function were measured by echocardiography, the hearts were isolated and left ventricular weight (LVW) was weighed. Azan staining was performed to measure cross-sectional diameter of cardiomyocytes. Activity of calcineurin, which dephosphorylates NFATc4, was measured by calcineurin phosphatase activity assay. Immunohistochemical staining was performed to evaluate nuclear translocation of NFATc4. Intracellular Ca²⁺ concentration in neonatal rat cardiomyocytes (NRCMs) was measured by using a calcium indicator. Canstatin significantly inhibited ISO-induced increase of LVW, left ventricular posterior wall thickness at end-diastole and diameter of cardiomyocytes. Canstatin significantly inhibited ISO-induced activation of calcineurin, nuclear translocation of NFATc4, increased mRNA expression of β-myosin heavy chain and α-skeletal actin, and intracellular Ca²⁺ rise in NRCMs. In summary, we for the first time demonstrated that canstatin administration suppresses ISO-induced cardiac hypertrophy possibly through the blockade of calcineurin/NFATc4 pathway in rats.

Optimal Isolation Method of Small Extracellular Vesicles from Rat Plasma

Small extracellular vesicles (sEVs) mediate cell–to–cell communication. We recently reported that circulating sEVs regulate systolic blood pressure in an animal model of human systemic hypertension. However, the underlying mechanisms still remain to be elucidated. As the first step for detailed analyses, we sought to increase the yield and purity of sEVs isolated from rat plasma. We compared the concentration and size distribution of sEVs as well as protein expression of the sEV marker and contaminants among plasma sEVs isolated by the ultracentrifugation (UC) method, the precipitation with polyethylene-glycol and ultracentrifugation (PEG-UC) method, or the precipitation with polyethylene-glycol (PEG) method. Effects of anticoagulants were also examined. The total concentration of plasma sEVs isolated by the PEG or PEG-UC method was much higher than that of the UC method. In the plasma sEVs isolated by the PEG-UC method, contaminating proteins were lower, while the protein expression of certain sEV markers was higher than that of the PEG method. There was no significant difference in total concentration or protein expression of sEV markers in sEVs isolated from rat plasma treated with three different anticoagulants (heparin, ethylenediaminetetraacetic acid, or acid citrate dextrose buffer) by the PEG-UC method. We, for the first time, determined that the PEG-UC method was optimal for sEV isolation from rat plasma.

Electro-Acupuncture Ameliorated MPTP-Induced Parkinsonism in Mice via TrkB Neurotrophic Signaling

Neurotrophins, such as brain-derived neurotrophic factor (BDNF), have shown promise as neuroprotective agents, indicating their potential in therapeutic strategies for neurodegenerative disease. However, the inherent bioactivity and pharmaceutical limitations of BDNF compromise its clinical efficacy. Research has documented the beneficial effects of electroacupuncture (EA) against neurodegeneration, possibly by BDNF-mediated mechanisms. The present study was designed to clarify whether EA can mount a neuroprotective effect in mice lesioned with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) via stimulation of the BDNF-TrkB signaling pathway. We found that EA not only ameliorated the motor dysfunction but also restored the dopaminergic neuronal function and upregulated BDNF expression in MPTP-lesioned mice. Interestingly, the TrkB inhibitor K252a abolished the neuroprotective effects of EA. Western blot analyses further demonstrated that EA might recover the level of phospho-Akt, phospho-ERK1/2, and BDNF against MPTP neurotoxicity via reversing the imbalance between TrkB FL and TrkB T1. Taken together, the results of the present study show that EA stimulation can ameliorate MPTP-induced parkinsonism in mice. Such a neuroprotective effect may be partially mediated via restoring TrkB neurotrophic signaling.

Cathepsin S degrades arresten and canstatin in infarcted area after myocardial infarction in rats

The basement membrane surrounding cardiomyocytes is mainly composed of α1 and α2 chain of type IV collagen. Arresten and canstatin are fragments of non-collagenous C-terminal domain of α1 and α2 chain, respectively. We previously reported that the expression of canstatin was decreased in infarcted area 2 weeks after myocardial infarction in rats. In the present study, we investigated the regulatory mechanism for expression of arresten and canstatin. Myocardial infarction model rats were produced by ligating left anterior descending artery. Western blotting and immunohistochemical staining were performed to determine the protein expression and distribution. Arresten and canstatin were highly expressed in the heart. One day and three days after myocardial infarction, the expression of arresten and canstatin in infarcted area was lower than that in non-infarcted area. The expression of cathepsin S, which is known to degrade arresten and canstatin, was increased in the infarcted area. A knockdown of cathepsin S gene using small interference RNA suppressed the decline of arresten and canstatin in the infarcted area 3 days after myocardial infarction. This study for the first time revealed that arresten and canstatin are immediately degraded by cathepsin S in the infarcted area after myocardial infarction. These findings present a novel fundamental insight into the pathogenesis of myocardial infarction through the turnover of basement membrane-derived endogenous factors.