Biomedical subjects

Haiheng Dong

Publications and source records attributed to Haiheng Dong.

6 recordsLinked to original sources

PubMed2007

Versican modulates gap junction intercellular communication.

Versican is a large chondroitin sulfate proteoglycan and belongs to the family of lecticans. Versican possesses two globular domains, G1 and G3 domain, separated by a CS-attachment region. The CS-attachment region present in the middle region is divided into two spliced domains named CSalpha and beta. Alternative splicing of versican generates at least four versican isoforms named V0, V1, V2, and V3. We have successfully cloned the full-length cDNA of chick versican isoforms V1 and V2 and found that versican isoform V1 induced mesenchymal-epithelial transition in NIH3T3 cells. Mesenchymal-epithelial transition induced by V1 in NIH3T3 cells is characterized by expression of E-cadherin and occludin, two epithelial markers, and reduced expression of fibroblastic marker vimentin (Sheng et al., 2006, Mol Biol Cell. 17, 2009-2020). In the present studies, we found that versican V1 isoform not only induced cell transition, but also increased intercellular communication via gap junction channels composed of connexin proteins. Our results showed that V1 induces plasma membrane localization of connexin 43, resulting in increased cell communication. This was further confirmed by blocking assays. Gap junctions mediated the transfer of small cytoplasmic molecules and the diffusion of second messenger molecules between adjacent cells. The ability of versican in regulating gap junction implied a potential role of versican in coordinating functions.

Animals↗

PubMed2006

Versican G3 domain regulates neurite growth and synaptic transmission of hippocampal neurons by activation of epidermal growth factor receptor.

Versican is one of the major extracellular matrix (ECM) proteins in the brain. ECM molecules and their cleavage products critically regulate the growth and arborization of neurites, hence adjusting the formation of neural networks. Recent findings have revealed that peptide fragments containing the versican C terminus (G3 domain) are present in human brain astrocytoma. The present study demonstrated that a versican G3 domain enhanced cell attachment, neurite growth, and glutamate receptor-mediated currents in cultured embryonic hippocampal neurons. In addition, the G3 domain intensified dendritic spines, increased the clustering of both synaptophysin and the glutamate receptor subunit GluR2, and augmented excitatory synaptic activity. In contrast, a mutated G3 domain lacking the epidermal growth factor (EGF)-like repeats (G3deltaEGF) had little effect on neurite growth and glutamatergic function. Treating the neurons with the G3-conditioned medium rapidly increased the levels of phosphorylated EGF receptor (pEGFR) and phosphorylated extracellular signal-regulated kinase (pERK), indicating an activation of EGFR-mediated signaling pathways. Blockade of EGFR prevented the G3-induced ERK activation and suppressed the G3-provoked enhancement of neurite growth and glutamatergic function but failed to block the G3-mediated enhancement of cell attachment. These combined results indicate that the versican G3 domain regulates neuronal attachment, neurite outgrowth, and synaptic function of hippocampal neurons via EGFR-dependent and -independent signaling pathway(s). Our findings suggest a role for ECM proteolytic products in neural development and regeneration.

Animals↗

PubMed2004

Excessive expression of acetylcholinesterase impairs glutamatergic synaptogenesis in hippocampal neurons.

Acetylcholinesterase (AChE) exerts noncatalytic activities on neural cell differentiation, adhesion, and neuritogenesis independently of its catalytic function. The noncatalytic functions of AChE have been attributed to its peripheral anionic site (PAS)-mediated protein-protein interactions. Structurally, AChE is highly homologous to the extracellular domain of neuroligin, a postsynaptic transmembrane molecule that interacts with presynaptic beta-neurexins, thus facilitating synaptic formation and maturation. Potential effects of AChE expression on synaptic transmission, however, remain unknown. Using electrophysiology, immunocytochemistry, and molecular biological approaches, this study investigated the role of AChE in the regulation of synaptic formation and functions. We found that AChE was highly expressed in cultured embryonic hippocampal neurons at early culture days, particularly in dendritic compartments including the growth cone. Subsequently, the expression level of AChE declined, whereas synaptic activity and synaptic proteins progressively increased. Chronic blockade of the PAS of AChE with specific inhibitors selectively impaired glutamatergic functions and excitatory synaptic structures independently of cholinergic activation, while inducing AChE overexpression. Moreover, the PAS blockade-induced glutamatergic impairments were associated with a depressed expression of beta-neurexins and an accumulation of other synaptic proteins, including neuroligins, and were mostly preventable by antisense suppression of AChE expression. Our findings demonstrate that interference with the nonenzymatic features of AChE alters AChE expression, which impairs excitatory synaptic structure and functions.

Acetylcholinesterase↗

PubMed2004

Versican V1 isoform induces neuronal differentiation and promotes neurite outgrowth.

The chondroitin sulfate proteoglycan versican is one of the major extracellular components in the developing and adult brain. Here, we show that isoforms of versican play different roles in neuronal differentiation and neurite outgrowth. Expression of versican V1 isoform in PC12 cells induced complete differentiation, whereas expression of V2 induced an aborted differentiation accompanied by apoptosis. V1 promoted neurite outgrowth of hippocampal neurons, but V2 failed to do so. V1 transfection enhanced expression of epidermal growth factor receptor and integrins, and facilitated sustained extracellular signal-regulated kinase/MAPK phosphorylation. Blockade of the epidermal growth factor receptor, beta1 integrin, or Src significantly inhibited neuronal differentiation. Finally, we demonstrated that versican V1 isoform also promoted differentiation of neural stem cells into neurons. Our results have implications for understanding how versican regulates neuronal development, function, and repair.

Animals↗

PubMed2002

Mutation of GABRA1 in an autosomal dominant form of juvenile myoclonic epilepsy.

Although many genes that predispose for epilepsy in humans have been determined, those that underlie the classical syndromes of idiopathic generalized epilepsy (IGE) have yet to be identified. We report that an Ala322Asp mutation in GABRA1, encoding the alpha1 subunit of the gamma-aminobutyric acid receptor subtype A (GABA(A)), is found in affected individuals of a large French Canadian family with juvenile myoclonic epilepsy. Compared with wildtype receptors, GABA(A) receptors that contain the mutant subunit show a lesser amplitude of GABA-activated currents in vitro, indicating that seizures may result from loss of function of this inhibitory ligand-gated channel. Our results confirm that mutation of GABRA1 predisposes towards a common idiopathic generalized epilepsy syndrome in humans.

Adolescent↗

PubMed2002

Mediation by nucleus tractus solitarii glutamatergic neurotransmission of the cardiovascular reflex evoked by distal esophageal distension.

Distention of the rat distal esophagus evokes an arterial pressor and a cardioaccelerator response that depends upon activation of a vagal afferent projection to the nucleus tractus solitarii (NTS). The present study aimed to determine in urethane-anesthetized rats if the afferent limb of this reflex (a) relays in the NTS subdivision known ro receive esophageal afferents, and (b) utilizes glutamatergic synapses. To this end, tetrodotoxin or the glutamate antagonists gamma-D-glutamyl-glycine, 6-7-dinitroquinoxaline-2,3-dione (DNQX) and 2-amino-5-phosphonovaleric acid (AP-5) were applied to the NTS extraventricular surface rostral to the obex. All four agents inhibited both components of the reflex. DNQX or AP-5 produced a similar reversible inhibition upon pressure ejection in the vagal esophageal afferent projection area. Application of tetrodotoxin to the dorsomedial medulla oblongata caudal to the area postrema (AP) was ineffective. Basal heart rate (HR) (except in the case of AP-5) and blood pressure increased upon NTS surface application of the antagonists but not after intra-NTS ejection. At corresponding dorsal NTS sites, focal excitation of solitarial neurons with glutamate evoked hypotension and cardiac slowing. At adjacent ventral sites in the NTS subnucleus centralis (NTSc) and/or its immediate vicinity, glutamate elicited an arterial pressor response that coincided with an esophageal contraction in most but not all cases. In conclusion, afferent fibers of the esophago-cardiovascular reflex (ECVR) probably (1) terminate in the vicinity of esophageal premotor neurons comprising the NTSc and (2) activate second-order neurons via glutamate receptors of both the NMDA and non-NMDA subtype.

Anesthetics, Local↗