Regulation of relaxin 3 gene expression via cAMP-PKA in a neuroblastoma cell line

Targeted viral vector transduction of relaxin-3 neurons in the rat nucleus incertus using a novel cell-type specific promoter

•

Extensive, ascending relaxin-3-containing neural networks are present throughout the rat forebrain.

•

Relaxin-3 signalling modulates complex behaviours and cognitive processes including feeding, anxiety and memory.

•

We tested a 1736 bp promoter sequence for specific transgene expression in relaxin-3 neurons of rat nucleus incertus (NI).

•

This promoter restricted m-Cherry marker expression to NI relaxin-3 neurons with 98% specificity.

•

This targeted transgene delivery offers a versatile method for ongoing preclinical studies of relaxin-3 circuitry.

Modern neuroscience utilizes transgenic techniques extensively to study the activity and function of brain neural networks. A key feature of this approach is its compatibility with molecular methods for selective transgene expression in neuronal circuits of interest. Until now, such targeted transgenic approaches have not been applied to the extensive circuitry involving the neuropeptide, relaxin-3. Pharmacological and gene knock-out studies have revealed relaxin-3 signalling modulates interrelated behaviours and cognitive processes, including stress and anxiety, food and alcohol consumption, and spatial and social memory, highlighting the potential of this system as a therapeutic target. In the present study, we aimed to identify a promoter sequence capable of regulating cell-type specific transgene expression from an adeno-associated viral (AAV) vector in relaxin-3 neurons of the rat nucleus incertus (NI). In parallel to relaxin-3 promoter sequences, we also tested an AAV vector containing promoter elements for the tropomyosin receptor kinase A (TrkA) gene, as TrkA is co-expressed with relaxin-3 in rat NI neurons. Stereotaxic injection of an mCherry-expressing AAV vector revealed widespread non-specific TrkA promoter (880 bp) activity in and adjacent to the NI at 8 weeks post-treatment. In contrast, mCherry expression was successfully restricted to relaxin-3 NI neurons with 98% specificity using a 1736 bp relaxin-3 promoter. In addition to detailed anatomical mapping of NI relaxin-3 networks, illustrated here in association with GABAergic medial septum neurons, this method for targeted transgene delivery offers a versatile tool for ongoing preclinical studies of relaxin-3 circuitry.

Relaxin-3/RXFP3 networks: an emerging target for the treatment of depression and other neuropsychiatric diseases?

Animal and clinical studies of gene-environment interactions have helped elucidate the mechanisms involved in the pathophysiology of several mental illnesses including anxiety, depression, and schizophrenia; and have led to the discovery of improved treatments. The study of neuropeptides and their receptors is a parallel frontier of neuropsychopharmacology research and has revealed the involvement of several peptide systems in mental illnesses and identified novel targets for their treatment. Relaxin-3 is a newly discovered neuropeptide that binds, and activates the G-protein coupled receptor, RXFP3. Existing anatomical and functional evidence suggests relaxin-3 is an arousal transmitter which is highly responsive to environmental stimuli, particularly neurogenic stressors, and in turn modulates behavioral responses to these stressors and alters key neural processes, including hippocampal theta rhythm and associated learning and memory. Here, we review published experimental data on relaxin-3/RXFP3 systems in rodents, and attempt to highlight aspects that are relevant and/or potentially translatable to the etiology and treatment of major depression and anxiety. Evidence pertinent to autism spectrum and metabolism/eating disorders, or related psychiatric conditions, is also discussed. We also nominate some key experimental studies required to better establish the therapeutic potential of this intriguing neuromodulatory signaling system, including an examination of the impact of RXFP3 agonists and antagonists on the overall activity of distinct or common neural substrates and circuitry that are identified as dysfunctional in these debilitating brain diseases.

Serotonin2C receptors in the nucleus accumbens are involved in enhanced alcohol-drinking behavior

Dopamine and serotonin (5-HT) in the nucleus accumbens (ACC) and ventral tegmental area of the mesoaccumbens reward pathways have been implicated in the mechanisms underlying development of alcohol dependence. We used a C57BL/6J mouse model with increased voluntary alcohol-drinking behavior by exposing the mice to alcohol vapor for 20 consecutive days. In the alcohol-exposed mice, the expression of 5-HT(2C) receptor mRNA increased in the ACC, caudate nucleus and putamen, dorsal raphe nucleus (DRN), hippocampus and lateral hypothalamus, while the protein level of 5-HT(2C) receptor significantly increased in the ACC. The expression of 5-HT(7) receptor mRNA increased in the ACC and DRN. Contents of 5-HT decreased in the ACC shell (ACC(S) ) and DRN of the alcohol-exposed mice. The basal extracellular releases of dopamine (DA) and 5-HT in the ACC(S) increased more in the alcohol-exposed mice than in alcohol-naïve mice. The magnitude of the alcohol-induced ACC(S) DA and 5-HT release in the alcohol-exposed mice was increased compared with the control mice. Intraperitoneal (i.p.) administration or local injection into ACC(S) of the 5-HT(2C) receptor antagonist, SB-242084, suppressed voluntary alcohol-drinking behavior in the alcohol-exposed mice. But the i.p. administration of the 5-HT(7) receptor antagonist, SB-258719, did not have significant effects on alcohol-drinking behavior in the alcohol-exposed mice. The effects of the 5-HT(2C) receptor antagonist were not observed in the air-exposed control mice. These results suggest that adaptations of the 5-HT system, especially the upregulation of 5-HT(2C) receptors in the ACC(S) , are involved in the development of enhanced voluntary alcohol-drinking behavior.

Minocycline inhibits D-amphetamine-elicited action potential bursts in a central snail neuron

Minocycline is a second-generation tetracycline that has been reported to have powerful neuroprotective properties. In our previous studies, we found that d-amphetamine (AMPH) elicited action potential bursts in an identifiable RP4 neuron of the African snail, Achatina fulica Ferussac. This study sought to determine the effects of minocycline on the AMPH-elicited action potential pattern changes in the central snail neuron, using the two-electrode voltage clamping method. Extracellular application of AMPH at 300 μM elicited action potential bursts in the RP4 neuron. Minocycline dose-dependently (300-900 μM) inhibited the action potential bursts elicited by AMPH. The inhibitory effects of minocycline on AMPH-elicited action potential bursts were restored by forskolin (50 μM), an adenylate cyclase activator, and by dibutyryl cAMP (N(6),2'-O-Dibutyryladenosine 3',5'-cyclic monophosphate; 1mM), a membrane-permeable cAMP analog. Co-administration of forskolin (50 μM) plus tetraethylammonium chloride (TEA; 5mM) or co-administration of TEA (5mM) plus dibutyryl cAMP (1mM) also elicited action potential bursts, which were prevented and inhibited by minocycline. In addition, minocycline prevented and inhibited forskolin (100 μM)-elicited action potential bursts. Notably, TEA (50mM)-elicited action potential bursts in the RP4 neuron were not affected by minocycline. Minocycline did not affect steady-state outward currents of the RP4 neuron. However, minocycline did decrease the AMPH-elicited steady-state current changes. Similarly, minocycline decreased the effects of forskolin-elicited steady-state current changes. Pretreatment with H89 (N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride; 10 μM), a protein kinase A inhibitor, inhibited AMPH-elicited action potential bursts and decreased AMPH-elicited steady-state current changes. These results suggest that the cAMP-protein kinase A signaling pathway and the steady-state current are involved in the inhibitory effects of minocycline upon AMPH-elicited action potential bursts.

p62/SQSTM1 in autophagic clearance of a non-ubiquitylated substrate

Proteolytic systems and the aggresome pathway contribute to preventing accumulation of cytotoxic aggregation-prone proteins. Although polyubiquitylation is usually required for degradation or aggresome formation, several substrates are processed independently of ubiquitin through a poorly understood mechanism. Here, we found that p62/SQSTM1, a multifunctional adaptor protein, was involved in the selective autophagic clearance of a non-ubiquitylated substrate, namely an aggregation-prone isoform of STAT5A (STAT5A_ΔE18). By using a cell line that stably expressed STAT5A_ΔE18, we investigated the properties of its aggregation and degradation. We found that STAT5A_ΔE18 formed non-ubiquitylated aggresomes and/or aggregates by impairment of proteasome functioning or autophagy. Transport of these aggregates to the perinuclear region was inhibited by trichostatin A or tubacin, inhibitors of histone deacetylase (HDAC), indicating that the non-ubiquitylated aggregates of STAT5A_ΔE18 were sequestered into aggresomes in an HDAC6-dependent manner. Moreover, p62 was bound to STAT5A_ΔE18 through its PB1 domain, and the oligomerization of p62 was required for this interaction. In p62-knockdown experiments, we found that p62 was required for autophagic clearance of STAT5A_ΔE18 but not for its aggregate formation, suggesting that the binding of p62 to non-ubiquitylated substrates might trigger their autophagic clearance.

Expression and translocation of aquaporin-2 in the endolymphatic sac in patients with Meniere's disease

Meniere's disease, characterised by episodic vertigo, fluctuating hearing loss and tinnitus, can occur under conditions of stress. Its pathology was first revealed to be inner ear hydrops through temporal bone studies in 1938. Although its pathogenesis has been proposed to be a disorder of water transport in the inner ear, subsequently, it remains unsolved, until now. A recent study revealed that both plasma stress hormone, vasopressin (pAVP) and its receptor, V2 (V2R) expression in the inner ear endolymphatic sac were significantly higher in Meniere's patients. In the present study, to link V2R-related molecules and inner ear hydrops, we examined V2R-linked water channel molecule, aquaporin-2 (AQP2) expression and translocation in human endolymphatic sac. AQP2 mRNA expression in the endolymphatic sac was significantly higher in Meniere's patients by using real-time polymerase chain reaction, as further confirmed by western blotting. AQP2-like immunoreactivity (-LIR) was translocated from luminal to basolateral side with endosomal trapping in the endolymphatic sac at the time of AVP exposure in human endolymphatic sac tissue culture. The similar AQP2-LIR translocation was also demonstrated by forskolin and blocked by vasopressin/V2R specific antagonist, OPC31260 and protein kinase A (PKA) specific antagonists, H-89 and KT-5720. We concluded that in the pathogenesis of inner ear hydrops resulting in Meniere's attacks, pAVP elevation as a result of stress and subsequent V2R-cAMP-PKA-AQP2 activation and endosomal trapping of AQP2 in the endolymphatic sac, might be important as a basis of this disease. Further experimental and clinical studies are needed to better clarify the neuroscientific relationship between stress and Meniere's disease.

A novel splicing variant form suppresses the activity of full-length signal transducer and activator of transcription 5A

Signal transducers and activators of transcription (STATs) regulate a variety of cellular functions, including differentiation and proliferation. STAT3 and STAT5 are known to play important roles in brain processes, such as energy homeostasis and neuronal development. We isolated a novel splicing variant of STAT5A from a cDNA library of the mouse brainstem. This variant, STAT5A_DeltaE18, lacked exon 18 and caused a frameshift in the C-terminus, resulting in deletion of a tyrosine phosphorylation site and a transactivation domain. Although the frameshift region had no characteristic motifs, it was highly serine/threonine-rich and contained a short proline-rich sequence. Expression of STAT5A_DeltaE18 was detected in the mouse brainstem, lung and thymus, but not in the mouse cerebrum or cerebellum. We developed a specific antibody against STAT5A_DeltaE18 and investigated the intracellular localization of this variant. STAT5A_DeltaE18 showed dot-like structures in the cytoplasm and could not translocate into the nucleus after prolactin treatment. STAT5A_DeltaE18 showed a strong tendency to aggregate, which led to coaggregation with STAT5A_full-length. This coaggregation inhibited the nuclear transport of STAT5A and suppressed prolactin-induced activation of STAT5A.