Female GluA3-KO mice show early onset hearing loss and afferent swellings in ambient sound levels

AMPA-type glutamate receptors (AMPAR) mediate excitatory cochlear transmission. However, the unique roles of AMPAR subunits are unresolved. Lack of subunit GluA3 (Gria3KO) in male mice reduced cochlear output by 8-weeks of age. Since Gria3 is X-linked and considering sex differences in hearing vulnerability, we hypothesized accelerated presbycusis in Gria3KO females. Here, auditory brainstem responses (ABR) were similar in 3-week-old female Gria3WT and Gria3KO mice. However, when raised in ambient sound, ABR thresholds were elevated and wave-1 amplitudes were diminished at 5-weeks and older in Gria3KO. In contrast, these metrics were similar between genotypes when raised in quiet. Paired synapses were similar in number, but lone ribbons and ribbonless synapses were increased in female Gria3KO mice in ambient sound compared to Gria3WT or to either genotype raised in quiet. Synaptic GluA4:GluA2 ratios increased relative to Gria3WT, particularly in ambient sound, suggesting an activity-dependent increase in calcium-permeable AMPARs in Gria3KO. Swollen afferent terminals were observed by 5-weeks only in Gria3KO females reared in ambient sound. We propose that lack of GluA3 induces sex-dependent vulnerability to AMPAR-mediated excitotoxicity.

Platelet-Rich Plasma Prevents In Vitro Transforming Growth Factor-β1-Induced Fibroblast to Myofibroblast Transition: Involvement of Vascular Endothelial Growth Factor (VEGF)-A/VEGF Receptor-1-Mediated Signaling †

The antifibrotic potential of platelet-rich plasma (PRP) is controversial. This study examined the effects of PRP on in vitro transforming growth factor (TGF)-β1-induced differentiation of fibroblasts into myofibroblasts, the main drivers of fibrosis, and the involvement of vascular endothelial growth factor (VEGF)-A in mediating PRP-induced responses. The impact of PRP alone on fibroblast differentiation was also assessed. Myofibroblastic phenotype was evaluated by confocal fluorescence microscopy and western blotting analyses of α-smooth muscle actin (sma) and type-1 collagen expression, vinculin-rich focal adhesion clustering, and stress fiber assembly. Notch-1, connexin 43, and VEGF-A expression were also analyzed by RT-PCR. PRP negatively regulated fibroblast-myofibroblast transition via VEGF-A/VEGF receptor (VEGFR)-1-mediated inhibition of TGF-β1/Smad3 signaling. Indeed TGF-β1/PRP co-treated fibroblasts showed a robust attenuation of the myofibroblastic phenotype concomitant with a decrease of Smad3 expression levels. The VEGFR-1 inhibition by KRN633 or blocking antibodies, or VEGF-A neutralization in these cells prevented the PRP-promoted effects. Moreover PRP abrogated the TGF-β1-induced reduction of VEGF-A and VEGFR-1 cell expression. The role of VEGF-A signaling in counteracting myofibroblast generation was confirmed by cell treatment with soluble VEGF-A. PRP as single treatment did not induce fibroblast myodifferentiation. This study provides new insights into cellular and molecular mechanisms underpinning PRP antifibrotic action.

Proliferative effects of melatonin on Schwann cells: implication for nerve regeneration following peripheral nerve injury

Activation of proliferation of Schwann cells is crucial for axonal guidance and successful nerve regeneration following peripheral nerve injury (PNI). Considering melatonin plays an important role in proliferative regulation of central glial cells, the present study determined whether melatonin can effectively promote Schwann cell proliferation and improve nerve regeneration after PNI. The spontaneous immortalized rat Schwann cell line (RSC 96 cells) was first analyzed by quantitative polymerase chain reaction (QPCR) to detect the potential existence of melatonin receptors. The melatonin receptor-mediated signaling responsible for proliferation was examined by measuring the phosphorylation of extracellular signal-regulated kinases (ERK1/2) pathway. The in vivo model of PNI was performed by the end-to-side neurorrhaphy. The quantity of Schwann cells as well as the number of re-innervated motor end plates (MEP) on target muscles was examined to represent the functional recovery of injured nerves. QPCR results indicated that MT1 is the dominant receptor in Schwann cells. Immunoblotting and proliferation assay revealed an enhanced phosphorylation of ERK1/2 and increased number of RSC 96 cells following melatonin administration. Nonselective melatonin receptor antagonist (luzindole) treatment significantly suppressed all the above findings, suggesting that the proliferative effects of melatonin were mediated by a receptor-dependent pathway. In vivo results corresponded well with in vitro findings in which melatonin effectively increased the amount of proliferated Schwann cells and re-innervated MEP on target muscles following PNI. As melatonin successfully improves nerve regeneration by promoting Schwann cell proliferation, therapeutic use of melatonin may thus serve as a promising strategy to counteract the PNI-induced neuronal disability.

Actin-binding Rho activating protein is expressed in the central nervous system of normal adult rats

Previous studies show that actin-binding Rho activating protein (Abra) is expressed in cardiomyocytes and vascular smooth muscle cells. In this study, we investigated the expression profile of Abra in the central nervous system of normal adult rats by confocal immunofluorescence. Results showed that Abra immunostaining was located in neuronal nuclei, cytoplasm and processes in the central nervous system, with the strongest staining in the nuclei; in the cerebral cortex, Abra positive neuronal bodies and processes were distributed in six cortical layers including molecular layer, external granular layer, external pyramidal layer, internal granular layer, internal pyramidal layer and polymorphic layer; in the hippocampus, the cell bodies of Abra positive neurons were distributed evenly in pyramidal layer and granular layer, with positive processes in molecular layer and orien layer; in the cerebellar cortex, Abra staining showed the positive neuronal cell bodies in Purkinje cell layer and granular layer and positive processes in molecular layer; in the spinal cord, Abra-immunopositive products covered the whole gray matter and white matter; co-localization studies showed that Abra was co-stained with F-actin in neuronal cytoplasm and processes, but weakly in the nuclei. In addition, in the hippocampus, Abra was co-stained with F-actin only in neuronal processes, but not in the cell body. This study for the first time presents a comprehensive overview of Abra expression in the central nervous system, providing insights for further investigating the role of Abra in the mature central nervous system.

Somatostatin-induced control of cytosolic free calcium in pituitary tumour cells

1. In rat pituitary tumour cells (GC cells), spontaneous oscillations of the intracellular concentration of Ca2+ ([Ca2+]i) induce growth hormone (GH) secretion that is inhibited by octreotide, a somatostatin (SRIF) agonist which binds to SRIF subtype (sst) receptor 2. The effects of its functional activation on the control of [Ca2+]i were investigated using fluorimetric measurements of [Ca2+]i. 2. SRIF decreases the basal [Ca2+]i and the [Ca2+]i rise in response to forskolin (FSK) through the inhibition of L-type voltage-dependent Ca2+ channels. 3. Pretreatment with octreotide or with L-Tyr8++ Cyanamid 154806, a sst2 receptor antagonist, abolishes the SRIF-induced inhibition of [Ca2+]i. Octreotide is known to operate through agonist-induced desensitization, while the antagonist operates through receptor blockade. 4. sst1 and sst2 receptor-immunoreactivities (-IRs) are localized to cell membranes. sst2, but not sst1 receptor-IR, internalizes after cell exposure to octreotide. 5. SRIF-induced inhibition of basal [Ca2+]i or FSK-induced Ca2+ entry is blocked by pertussis toxin (PTX). 6. FSK-induced cyclic AMP accumulation is only partially decreased by SRIF or octreotide, indicating that sst2 receptors are coupled to intracellular pathways other than adenylyl cyclase (AC) inhibition. 7. In the presence of H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA), SRIF-induced inhibition of basal [Ca2+]i is still present, although reduced in amplitude. 8. SRIF inhibits [Ca2+]i by activating sst2 receptors. Inhibition of AC activity is only partly responsible for this effect, and other transduction pathways may be involved.