Brain-derived neurotrophic factor in higher vertebrate pancreas: immunolocalization in glucagon cells

Electroacupuncture and Moxibustion Modulate the BDNF and TrkB Expression in the Colon and Dorsal Root Ganglia of IBS Rats with Visceral Hypersensitivity

Objective

To evaluate the effects of electroacupuncture and moxibustion on brain-derived neurotrophic factor (BDNF) and its receptor tyrosine kinase receptor B (TrkB) protein and mRNA expressions in the colon and dorsal root ganglia of IBS rats with visceral hypersensitivity and to explore their underlying therapeutic mechanisms.

Method

Forty Sprague Dawley rats were randomly divided into normal, model, model + mild moxibustion (MM), model + electroacupuncture (EA), and model + pinaverium bromide (PB) groups, with eight rats in each group. Chronic visceral hypersensitive IBS rat models were established by colorectal distension (CRD) with mustard oil clyster. Rats in the MM and EA groups, respectively, received moxibustion and electroacupuncture treatments on the Tianshu (ST25) and Shangjuxu (ST37) acupoints once daily for 7 days, and rats in the PB group received pinaverium bromide by oral gavage once daily for 7 consecutive days. After treatment, rats underwent abdominal withdrawal reflex (AWR) scoring under CRD and colon histopathological examination. Immunohistochemistry and real-time quantitative PCR (RT-qPCR) were used to study the protein and mRNA expressions of BDNF and TrkB in the rat colon and dorsal root ganglia.

Results

Compared with the normal group, AWR scores and body weight were clearly increased in the model group rats (both P < 0.01). The body weights were significantly elevated (P < 0.01, P < 0.05), but the AWR scores were reduced (P < 0.05, P < 0.01), after electroacupuncture and mild moxibustion treatment. Compared with levels in normal rats, BDNF and TrkB protein and mRNA expressions were significantly elevated in the IBS model rats (P < 0.01) but were downregulated after mild moxibustion, electroacupuncture, and Western medicine treatment (P < 0.01).

Conclusion

Electroacupuncture and moxibustion improved visceral hypersensitivity of IBS rats possibly by reducing BDNF and TrkB protein and mRNA expressions in the colon and dorsal root ganglia.

Diabetes mellitus, cognitive deficits and serum BDNF levels in chronic patients with schizophrenia: A case-control study

The relationship between serum BDNF levels and cognitive dysfunction in schizophrenia (SCZ) patients comorbid with type 2 diabetes mellitus (T2DM) has not been reported. Hence, this study aimed to explore whether and how the changes of serum BDNF levels were correlated with cognitive impairment in SCZ patients comorbid with T2DM. We recruited 472 inpatients with chronic SCZ (54 T2DM and 418 non-T2DM), and 225 healthy controls. Serum BDNF levels and routine biochemical parameters were measured. Psychopathological symptoms were evaluated by the Positive and Negative Syndrome Scale (PANSS) and cognitive function was assessed by the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). SCZ patients with T2DM had significantly higher serum BDNF levels than SCZ patients without T2DM (F = 11.31, p = 0.001). SCZ patients with T2DM scored higher in delayed memory than SCZ patients without T2DM (77.17 ± 18.44 vs.66.24 ± 19.51, p = 0.000), and still showed significance after controlling for confounders. Further stepwise multiple regression analysis identified serum BDNF as an independent contributor to the RBANS attention of SCZ patients with T2DM (β = 0.30, t = 2.09, p = 0.042). The increase of BDNF levels and better cognitive performance, especially delayed memory, may be related to the pathophysiological process of T2DM in chronic SCZ patients.

Metallothionein-3 as a multifunctional player in the control of cellular processes and diseases

Transition metals, such as iron, copper, and zinc, play a very important role in life as the regulators of various physiochemical reactions in cells. Abnormal distribution and concentration of these metals in the body are closely associated with various diseases including ischemic seizure, Alzheimer's disease, diabetes, and cancer. Iron and copper are known to be mainly involved in in vivo redox reaction. Zinc controls a variety of intracellular metabolism via binding to lots of proteins in cells and altering their structure and function. Metallothionein-3 (MT3) is a representative zinc binding protein predominant in the brain. Although the role of MT3 in other organs still needs to be elucidated, many reports have suggested critical roles for the protein in the control of a variety of cellular homeostasis. Here, we review various biological functions of MT3, focusing on different cellular molecules and diseases involving MT3 in the body.

Brain-derived neurotrophic factor: A steroidogenic regulator of Leydig cells

The brain-derived neurotrophic factor (BDNF) was first recognized for its roles in the peripheral and central nervous systems, and its complex functions on mammalian organs have been extended constantly. However, to date, little is known about its effects on the male reproductive system, including the steroidogenesis of mammals. The purpose of this study was to elucidate the effects of BDNF on testosterone generation of Leydig cells and the underlying mechanisms. We found that BDNF-induced proliferation of TM3 Leydig cells via upregulation of proliferating cell nuclear antigen ( Pcna) and promoted testosterone generation as a result of upregulation of steroidogenic acute regulatory protein ( Star), 3b-hydroxysteroid dehydrogenase ( Hsd3b1), and cytochrome P450 side-chain cleavage enzyme ( Cyp11a1) both in primary Leydig cells and TM3 Leydig cells, which were all attenuated in Bdnf knockdown TM3 Leydig cells. Furthermore, the possible mechanism of testosterone synthesis was explored in TM3 Leydig cells. The results showed that BDNF enhanced extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) phosphorylation, and the effect was disrupted by Bdnf deletion. Moreover, PD98059, a potent selective inhibitor of ERK1/2 activation, compromised BDNF-induced testosterone generation and upregulation of Star, Hsd3b1, and Cyp11a1. The Bdnf knockdown assay, on the other hand, indicated the autocrine effect of BDNF on steroidogenesis in TM3 Leydig cells. On the basis of these results, we concluded that BDNF, acting as an autocrine factor, induced testosterone generation as a result of the upregulation of Star, Hsd3b1, and Cyp11a1 via stimulation of the ERK1/2 pathway.

Anti-diabetic and neuroprotective effects of pancreatic islet transplantation into the central nervous system

During the last decades, the central nervous system (CNS) was intensively tested as a site for islet transplantation in different animal models of diabetes. Immunoprivilege properties of intracranial and intrathecal sites were found to delay and reduce rejection of transplanted allo-islets and xeno-islets, especially in the form of dispersed single cells. Insulin released from islets grafted in CNS was shown to cross the blood-brain barrier and to act as a regulator of peripheral glucose metabolism. In diabetic animals, sufficient nutrition and oxygen supply to islets grafted in the CNS provide adequate insulin response to increase glucose level resulting in rapid normoglycemia. In addition to insulin, pancreatic islets produce and secrete several other hormones, as well as neurotrophic and angiogenic factors with potential neuroprotective properties. Recent experimental studies and clinical trials provide a strong support for delivery of islet-derived macromolecules to CNS as a promising strategy to treat various brain disorders. This review article focuses mainly on analysis of current status of intracranial and intrathecal islet transplantations for treatment of experimental diabetes and discusses the possible neuroprotective properties of grafted islets into CNS as a novel therapeutic approach to brain disorders with cognitive dysfunctions characterized by impaired brain insulin signalling. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of moderate- and high-intensity chronic exercise on brain-derived neurotrophic factor expression in fast and slow muscles

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) protein expression is sensitive to cellular activity. In the sedentary state, BDNF expression is affected by the muscle phenotype.

METHODS

Eighteen Wistar rats were divided into the following 3 groups: sedentary (S); moderate-intensity training (MIT); and high-intensity training (HIT). The training protocol lasted 8 weeks. Forty-eight hours after training, total RNA and protein levels in the soleus and plantaris muscles were obtained.

RESULTS

In the plantaris, the BDNF protein level was lower in the HIT than in the S group (P < 0.05). A similar effect was found in the soleus (without significant difference). In the soleus, higher Bdnf mRNA levels were found in the HIT group (P < 0.001 vs. S and MIT groups). In the plantaris muscle, similar Bdnf mRNA levels were found in all groups.

CONCLUSIONS

These results indicate that high-intensity chronic exercise reduces BDNF protein level in fast muscles and increases Bdnf mRNA levels in slow muscles.

Intracranial pancreatic islet transplantation increases islet hormone expression in the rat brain and attenuates behavioral dysfunctions induced by MK-801 (dizocilpine)

The treatment of rodents with non-competitive antagonist of the N-Methyl-D-aspartate (NMDA) receptor, MK-801 (dizocilpine), induces symptoms of psychosis, deficits in spatial memory and impairment of synaptic plasticity. Recent studies have suggested that insulin administration might attenuate the cognitive dysfunctions through the modulatory effect on the expression of NMDA receptors and on the brain insulin signaling. Intrahepatic pancreatic islet transplantation is known as an efficient tool for correcting impaired insulin signaling. We examined the capacity of syngeneic islets grafted into the cranial subarachnoid cavity to attenuate behavioral dysfunctions in rats exposed to MK-801. Animals were examined in the open field (OF) and the Morris Water Maze (MWM) tests following acute or subchronic administration of MK-801. We found well-vascularized grafted islets expressing insulin, glucagon and somatostatin onto the olfactory bulb and prefrontal cortex. Significantly higher levels of insulin were detected in the hippocampus and prefrontal cortex of transplanted animals compared to the non-transplanted rats. All animals expressed normal peripheral glucose homeostasis for two months after transplantation. OF tests revealed that rats exposed to MK-801 treatment, showed hyper-responsiveness in motility parameters and augmented center field exploration compared to intact controls and these effects were attenuated by the grafted islets. Moreover, in the MWM, the rats treated with MK-801 showed impairment of spatial memory that were partially corrected by the grafted islets. In conclusion, intracranial islet transplantation leads to the expression of islet hormones in the brain and attenuates behavioral and cognitive dysfunctions in rats exposed to MK-801 administration without altering the peripheral glucose homeostasis.

The role of metallothionein-3 in streptozotocin-induced beta-islet cell death and diabetes in mice

Metallothionein-3 (Mt3), a zinc (Zn)-regulatory protein mainly expressed in the central nervous system, may contribute to oxidative cell death. In the present study, we examined the possible role of Mt3 in streptozotocin (STZ)-induced islet cell death and consequent hyperglycemia. Quantitative real-time polymerase chain reaction (RT-PCR) confirmed that islet cells expressed Mt3 mRNA. In all cases, wild-type (WT) mice injected with STZ exhibited hyperglycemia 7-21 days later. In stark contrast, all Mt3-null mice remained normoglycemic following STZ injection. STZ treatment increased free Zn levels in islet cells and induced their death in WT mice, but failed to do so in Mt3-null mice. Consistent with this, cultured Mt3-null islet cells exhibited striking resistance to STZ toxicity. Notably, PDE3a (phosphodiesterase 3A) was downregulated in islets of Mt3-null mice compared to those of WT mice, and was not induced by STZ treatment. Moreover, the PDE3 inhibitor cilostazol reduced islet cell death, likely by increasing cAMP levels, further supporting a role for PDE3 in STZ-induced islet cell death. Collectively, these results demonstrate that Mt3 may act through PDE3a to play a key role in Zn dyshomeostasis and cell death in STZ-treated islets.

Chronic exercise increases plasma brain-derived neurotrophic factor levels, pancreatic islet size, and insulin tolerance in a TrkB-dependent manner

BACKGROUND

Physical exercise improves glucose metabolism and insulin sensitivity. Brain-derived neurotrophic factor (BDNF) enhances insulin activity in diabetic rodents. Because physical exercise modifies BDNF production, this study aimed to investigate the effects of chronic exercise on plasma BDNF levels and the possible effects on insulin tolerance modification in healthy rats.

METHODS

Wistar rats were divided into five groups: control (sedentary, C); moderate- intensity training (MIT); MIT plus K252A TrkB blocker (MITK); high-intensity training (HIT); and HIT plus K252a (HITK). Training comprised 8 weeks of treadmill running. Plasma BDNF levels (ELISA assay), glucose tolerance, insulin tolerance, and immunohistochemistry for insulin and the pancreatic islet area were evaluated in all groups. In addition, Bdnf mRNA expression in the skeletal muscle was measured.

PRINCIPAL FINDINGS

Chronic treadmill exercise significantly increased plasma BDNF levels and insulin tolerance, and both effects were attenuated by TrkB blocking. In the MIT and HIT groups, a significant TrkB-dependent pancreatic islet enlargement was observed. MIT rats exhibited increased liver glycogen levels following insulin administration in a TrkB-independent manner.

CONCLUSIONS/SIGNIFICANCE

Chronic physical exercise exerted remarkable effects on insulin regulation by inducing significant increases in the pancreatic islet size and insulin sensitivity in a TrkB-dependent manner. A threshold for the induction of BNDF in response to physical exercise exists in certain muscle groups. To the best of our knowledge, these are the first results to reveal a role for TrkB in the chronic exercise-mediated insulin regulation in healthy rats.

Neurotrophin signaling and visceral hypersensitivity

Neurotrophin family are traditionally recognized for their nerve growth promoting function and are recently identified as crucial factors in regulating neuronal activity in the central and peripheral nervous systems. The family members including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) are reported to have distinct roles in the development and maintenance of sensory phenotypes in normal states and in the modulation of sensory activity in disease. This paper highlights receptor tyrosine kinase (Trk) -mediated signal transduction by which neurotrophins regulate neuronal activity in the visceral sensory reflex pathways with emphasis on the distinct roles of NGF and BDNF signaling in physiologic and pathophysiological processes. Viscero-visceral cross-organ sensitization exists widely in human diseases. The role of neurotrophins in mediating neural cross talk and interaction in primary afferent neurons in the dorsal root ganglia (DRG) and neurotrophin signal transduction in the context of cross-organ sensitization are also discussed.

Cellular localization of GDNF and its GFRalpha1/RET receptor complex in the developing pancreas of cat

Glial cell line-derived neurotrophic factor (GDNF) acts through RET receptor tyrosine kinase and its co-receptor GFRalpha1. In an effort to better understand the possible biological contribution of the GDNF and GFRalpha1/RET complex in pancreatic development, in this study we report the cellular localization of these proteins in the pancreas of domestic cat embryos and fetuses by immunocytochemical methods. In early embryos, GDNF, GFRalpha and RET immunoreactivity (IR) was localized in closely intermingled cells. GDNF and RET immunoreactive cells displayed chromogranin (an endocrine marker) and PGP 9.5 (a neuronal marker) IR, respectively. GFRalpha IR was present in both a few GDNF/chromogranin and RET/PGP 9.5 immunoreactive cells. In elderly fetuses, GDNF and GFRalpha IR were co-localized in glucagon cells and RET IR was detected in few neurons and never co-localized with GFRalpha or GDNF IR. In early embryos, the presence of GDNF IR in chromogranin immunoreactive cells and GFRalpha1/RET complex IR in PGP9.5 immunoreactive cells seems to suggest a paracrine action of GDNF contained in endocrine cell precursors on neuronal cell precursors expressing its receptor complex. The presence in different cell populations of RET and its co-receptor GFRalpha1 IR could be due to independent signaling of GRFalpha1. Thus, the co-presence of GDNF and GFRalpha1 in chromogranin and glucagon cells could lead to the hypothesis that GDNF can act in an autocrinal manner. In fetuses, RET IR was detected only in intrapancreatic ganglia. Because of the lack of GFRalpha1 IR in pancreatic innervation, RET receptor could be activated by other GFR alphas and ligands of GDNF family. In conclusion, these findings suggest that in differently aged embryos and fetuses the GDNF signal is differently mediated by RET and GFRalpha1.

The development of avian enteric nervous system: distribution of artemin immunoreactivity

Among the factors that control neural crest cell precursors within the enteric nervous system, the ligands of the glial cell line-derived neurotrophic factor family (GFL) seem to be the most influential. Artemin, a member of the GFLs, was previously described only in the oesophagus and stomach of mouse embryos. In this study, the presence and distribution of artemin is reported in duck embryos and adults. Artemin immunoreactivity was apparent in the intestinal tract at embryonic day 7 (d7), firstly in the myenteric plexus and then in the submucous plexus. Later, artemin immunoreactive nerve fibres were also seen in the longitudinal muscle plexus, the circular muscle plexus, the plexus of the muscularis mucosa and in the mucosal plexus. Furthermore, at d7, weak labeling of artemin was detected in neurons and glial cells in the oesophagus, gastric region and duodenum. Subsequently, artemin was also detected in all other intestinal segments. Moreover, during development of the gut in the domestic duck, artemin immunoreactivity decreased in neuronal cell bodies, whilst it increased in neuronal fibres and glial cells. These findings suggest an involvement of artemin in the development and biology of the gut of the domestic duck.

Effects of castration on the expression of brain-derived neurotrophic factor (BDNF) in the vas deferens and male accessory genital glands of the rat

Brain-derived neurotrophic factor (BDNF) is a growth factor belonging to the family of neurotrophins. Although neurotrophins in the male genital organs have been well documented, their role in the biology of these organs is far from clear. In particular, little is known about the influence of sex hormones on neurotrophin expression. In the present study, using immunohistochemistry and enzyme-linked immunosorbent assay (ELISA), we investigated the distribution and tissue concentration of BDNF in the vas deferens and accessory male genital glands in normal and castrated rats. The expression of BDNF mRNA was also investigated. In normal rats, BDNF immunoreactivity was localized in the musculature of the vas deferens and vesicular gland and in the fibromuscular stromal cells of the prostate. In the ventral prostatic lobes, BDNF immunoreactivity was localized in basal, secretory and neuroendocrine epithelial cells. Innervating ganglia and nerves were immunoreactive in all the examined tracts. After castration, BDNF immunoreactivity increased in the musculature of the vesicular gland and in the fibromuscular stromal cells of both dorsal and ventral prostatic lobes. BDNF immunoreactivity also increased in the nerves. ELISA and reverse transcription/real-time polymerase chain reaction confirmed the findings of the immunohistochemical study. In the accessory glands, castration induced an increase of both BDNF tissue concentration and mRNA expression. These results suggest that BDNF is expressed in the internal male genital organs of the rat and that its expression is downregulated by androgen hormones. We hypothesize that the observed BDNF increases are related to the castration-induced regression of the sympathetic nerves.

Neurotrophins in clinical diagnostics: pathophysiology and laboratory investigation

There is now growing evidence that a number of multifunctional signaling molecules, originally discovered as signal molecules in specific cells, exert their effects in various other tissue compartments. Neurotrophins, a class of homologues growth factors initially discovered to promote neuronal growth and survival, display such a dual activity and contribute to the development of a variety of non-neuronal tissues. Nowadays, several examples of essential non-neuronal functions played by neurotrophins and of variations of neurotrophin expression that accompany these processes can be presented. As will be shown, neurotrophins are found in many body tissues produced by a variety of non-neuronal cell types such as immune cells, adipocytes, endothelia, epithelia, fibroblasts, keratinocytes and endocrine cells. Assuming a general role as growth and survival factors, changes in neurotrophin expression may reflect physiological or pathological processes, such as activation, proliferation or repair followed by injury in the tissues. Neurotrophins were also present in the systemic blood circulation and variations in blood concentrations indicate vascular as well as peripheral production. In this review, we will discuss changes in local and systemic neurotrophin concentrations as well as their known pathophysiological relationship in various inflammatory and non-inflammatory disorders. Beside the nervous system, these will include diseases of the airways, skin and joints as well as systemic autoimmune diseases. Furthermore, new aspects of neurotrophin actions in maintenance of body energy balance and in reproductive endocrinology will be presented.

Brain-derived neurotrophic factor (BDNF) gene delivery into the CNS using bone marrow cells as vehicles in mice

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, is protective in animal models of neurodegenerative diseases. However, BDNF has a short half-life and its efficacy in the CNS when delivered peripherally is limited due to the blood-brain barrier. In the present study, bone marrow cells were used as vehicles to deliver the BDNF gene into the CNS. Marrow cells obtained from 6 to 8 week-old SJL/J mice were transduced with BDNF expressing pro-virus. RT-PCR analysis revealed that BDNF mRNA was expressed in transduced but not in non-transduced marrow cells. Additionally, virus transduced marrow cells expressed the BDNF protein (296+/-1.2 unit/ml). BDNF-transduced marrow cells were then transplanted into irradiated mice through the tail vein. Three months post-transplantation, significant increases in BDNF as well as glutamic acid decarboxylase (GAD(67)) mRNA were detected in the brains of BDNF transplanted mice compared to untransplanted animals, indicating biological activity of the BDNF transgene. Thus, bone marrow cells can be used as vehicles to deliver the BDNF gene into the brain with implications for the treatment of neurological diseases.

Neurotrophin presence in human coronary atherosclerosis and metabolic syndrome: a role for NGF and BDNF in cardiovascular disease?

The development of atherosclerotic cardiovascular disease is a common comorbidity in patients with the metabolic syndrome, a concurrence of cardiovascular risk factors in one individual. While multiple growth factors and adipokines are identified in atherosclerotic lesions, as well as neurotrophins implicated in both cardiac ischemia and lipid and glucose metabolism, the potential role of neurotrophins in human coronary atherosclerosis and in the metabolic syndrome still remains to be elucidated. Here we describe and discuss our results that represent a novel attempt to study the cardiovascular and metabolic biology of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and mast cells (MC). The local amount of NGF, the immunolocalization of p75 neurotrophin receptor (p75NTR) and the number of MC were correlatively examined in coronary vascular wall and in the surrounding subepicardial adipose tissue, obtained from autopsy cases in humans with advanced coronary atherosclerosis. We also analyzed the plasma levels of NGF, BDNF and leptin and the number of MC in biopsies from abdominal subcutaneous adipose tissue in patients with a severe form of the metabolic syndrome. The results demonstrate that NGF levels are decreased in atherosclerotic coronary vascular tissue but increased in the subepicardial adipose tissue, whereas both tissues express a greater number of MC and a stronger p75NTR immunoreactivity, compared to controls. Metabolic syndrome patients display a significant hyponeurotrophinemia and an increased number of adipose MC; the later correlates with elevated plasma leptin levels. In effect, we provide the first evidence for (i) an altered presence of NGF, p75NTR and MC in both coronary vascular and subepicardial adipose tissue in human coronary atherosclerosis, and (ii) a significant decrease in plasma NGF and BDNF levels and an elevated amount of plasma leptin and adipose MC in metabolic syndrome patients. Together our findings suggest that neuroimmune mediators such as NGF, BDNF, leptin and MC may be involved in the development of cardiovascular disease and related disorders.