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Shi-Hua Li

Publications and source records attributed to Shi-Hua Li.

At least 19 recordsLinked to original sources
PubMed2006

Context-dependent dysregulation of transcription by mutant huntingtin.

Huntington disease (HD) is an adult-onset neurodegenerative disease caused by expansion of a polyglutamine (poly(Q) tract in the N-terminal region of huntingtin (htt). Although the precise mechanisms leading to neurodegeneration in HD have not been fully elucidated, transcriptional dysregulation has been implicated in disease pathogenesis. In HD, multiple N-terminal mutant htt fragments smaller than the first 500 amino acids have been found to accumulate in the nucleus and adversely affect gene transcription. It is unknown whether different htt fragments in the nucleus can differentially bind transcription factors and affect transcription. Here, we report that shorter N-terminal htt fragments, which are more prone to misfolding and aggregation, are more competent to bind Sp1 and inhibit its activity. These effects can be reversed by Hsp40, a molecular chaperone that reduces the misfolding of mutant htt. Our results provide insight into the beneficial effects of molecular chaperones and suggest that context dependent transcriptional dysregulation may contribute to differential toxicity of various N-terminal htt fragments.

Animals↗
PubMed2006

Regulation of intracellular trafficking of huntingtin-associated protein-1 is critical for TrkA protein levels and neurite outgrowth.

Mutant huntingtin can affect vesicular and receptor trafficking via its abnormal protein interactions, suggesting that impairment of intracellular trafficking may contribute to Huntington's disease. There is growing evidence that huntingtin-associated protein-1 (HAP1) also interacts with microtubule-dependent transporters and is involved in intracellular trafficking. However, it remains unclear how the trafficking of HAP1 is regulated and contributes to neuronal function. Here we report that phosphorylation of HAP1 decreases its association with microtubule-dependent transport proteins dynactin p150 and kinesin light chain and reduces its localization in neurite tips. Suppressing HAP1 expression by RNA interference reduces neurite outgrowth and the level of tropomyosin-related kinase A receptor tyrosine kinase (TrkA), a nerve growth factor receptor whose internalization and trafficking are required for neurite outgrowth. HAP1 maintains the normal level of membrane TrkA by preventing the degradation of internalized TrkA. Mutant huntingtin also reduces the association of HAP1 with dynactin p150 and kinesin light chain and thereby decreases the intracellular level of TrkA. These findings suggest that HAP1 trafficking is critical for the stability of TrkA and neurite function, both of which can be attenuated by mutant huntingtin.

Animals↗
PubMed2006

Hypothalamic huntingtin-associated protein 1 as a mediator of feeding behavior.

The hypothalamus responds to circulating leptin and insulin in the control of food intake and body weight. A number of neurotransmitters in the hypothalamus, including gamma-aminobutyric acid (GABA), also have key roles in feeding. Huntingtin-associated protein 1 (Hap1) is expressed more abundantly in the hypothalamus than in other brain regions, and lack of Hap1 in mice leads to early postnatal death. Hap1 is also involved in intracellular trafficking of the GABA(A) receptor. Here, we report that fasting upregulates the expression of Hap1 in the rodent hypothalamus, whereas intracerebroventricular administration of insulin downregulates Hap1 by increasing its degradation through ubiquitination. Decreasing the expression of mouse hypothalamic Hap1 by siRNA reduces the level and activity of hypothalamic GABA(A) receptors and causes a decrease in food intake and body weight. These findings provide evidence linking hypothalamic Hap1 to GABA in the stimulation of feeding and suggest that this mechanism is involved in the feeding-inhibitory actions of insulin in the brain.

Animals↗
PubMed2006

The prolyl isomerase Pin1 regulates amyloid precursor protein processing and amyloid-beta production.

Neuropathological hallmarks of Alzheimer's disease are neurofibrillary tangles composed of tau and neuritic plaques comprising amyloid-beta peptides (Abeta) derived from amyloid precursor protein (APP), but their exact relationship remains elusive. Phosphorylation of tau and APP on certain serine or threonine residues preceding proline affects tangle formation and Abeta production in vitro. Phosphorylated Ser/Thr-Pro motifs in peptides can exist in cis or trans conformations, the conversion of which is catalysed by the Pin1 prolyl isomerase. Pin1 has been proposed to regulate protein function by accelerating conformational changes, but such activity has never been visualized and the biological and pathological significance of Pin1 substrate conformations is unknown. Notably, Pin1 is downregulated and/or inhibited by oxidation in Alzheimer's disease neurons, Pin1 knockout causes tauopathy and neurodegeneration, and Pin1 promoter polymorphisms appear to associate with reduced Pin1 levels and increased risk for late-onset Alzheimer's disease. However, the role of Pin1 in APP processing and Abeta production is unknown. Here we show that Pin1 has profound effects on APP processing and Abeta production. We find that Pin1 binds to the phosphorylated Thr 668-Pro motif in APP and accelerates its isomerization by over 1,000-fold, regulating the APP intracellular domain between two conformations, as visualized by NMR. Whereas Pin1 overexpression reduces Abeta secretion from cell cultures, knockout of Pin1 increases its secretion. Pin1 knockout alone or in combination with overexpression of mutant APP in mice increases amyloidogenic APP processing and selectively elevates insoluble Abeta42 (a major toxic species) in brains in an age-dependent manner, with Abeta42 being prominently localized to multivesicular bodies of neurons, as shown in Alzheimer's disease before plaque pathology. Thus, Pin1-catalysed prolyl isomerization is a novel mechanism to regulate APP processing and Abeta production, and its deregulation may link both tangle and plaque pathologies. These findings provide new insight into the pathogenesis and treatment of Alzheimer's disease.

Alzheimer Disease↗
PubMed2005

Expression of mutant huntingtin in glial cells contributes to neuronal excitotoxicity.

Huntington disease (HD) is characterized by the preferential loss of striatal medium-sized spiny neurons (MSNs) in the brain. Because MSNs receive abundant glutamatergic input, their vulnerability to excitotoxicity may be largely influenced by the capacity of glial cells to remove extracellular glutamate. However, little is known about the role of glia in HD neuropathology. Here, we report that mutant huntingtin accumulates in glial nuclei in HD brains and decreases the expression of glutamate transporters. As a result, mutant huntingtin (htt) reduces glutamate uptake in cultured astrocytes and HD mouse brains. In a neuron-glia coculture system, wild-type glial cells protected neurons against mutant htt-mediated neurotoxicity, whereas glial cells expressing mutant htt increased neuronal vulnerability. Mutant htt in cultured astrocytes decreased their protection of neurons against glutamate excitotoxicity. These findings suggest that decreased glutamate uptake caused by glial mutant htt may critically contribute to neuronal excitotoxicity in HD.

Adult↗
PubMed2005

Interaction of Huntingtin-associated protein-1 with kinesin light chain: implications in intracellular trafficking in neurons.

Huntingtin-associated protein-1 (HAP1) was initially identified as an interacting partner of huntingtin, the Huntington disease protein. Unlike huntingtin that is ubiquitously expressed throughout the brain and body, HAP1 is enriched in neurons, suggesting that its dysfunction could contribute to Huntington disease neuropathology. Growing evidence has demonstrated that HAP1 and huntingtin are anterogradely transported in axons and that the abnormal interaction between mutant huntingtin and HAP1 may impair axonal transport. However, the exact role of HAP1 in anterograde transport remains unclear. Here we report that HAP1 interacts with kinesin light chain, a subunit of the kinesin motor complex that drives anterograde transport along microtubules in neuronal processes. The interaction of HAP1 with kinesin light chain is demonstrated via a yeast two-hybrid assay, glutathione S-transferase pull down, and coimmunoprecipitation. Furthermore, HAP1 is colocalized with kinesin in growth cones of neuronal cells. We also demonstrated that knocking down HAP1 via small interfering RNA suppresses neurite outgrowth of PC12 cells. Analysis of live neuronal cells with fluorescence microscopy and fluorescence recovery after photobleaching demonstrates that suppressing the expression of HAP1 or deleting the HAP1 gene inhibits the kinesin-dependent transport of amyloid precursor protein vesicles. These studies provide a molecular basis for the participation of HAP1 in anterograde transport in neuronal cells.

Amyloid beta-Protein Precursor↗
PubMed2005

Contribution of nuclear and extranuclear polyQ to neurological phenotypes in mouse models of Huntington's disease.

In postmortem Huntington's disease brains, mutant htt is present in both nuclear and cytoplasmic compartments. To dissect the impact of nuclear and extranuclear mutant htt on the initiation and progression of disease, we generated a series of transgenic mouse lines in which nuclear localization or nuclear export signal sequences have been placed N-terminal to the htt exon 1 protein carrying 144 glutamines. Our data indicate that the exon 1 mutant protein is present in the nucleus as part of an oligomeric or aggregation complex. Increasing the concentration of the mutant transprotein in the nucleus is sufficient for and dramatically accelerates the onset and progression of behavioral phenotypes. Furthermore, nuclear exon 1 mutant protein is sufficient to induce cytoplasmic neurodegeneration and transcriptional dysregulation. However, our data suggest that cytoplasmic mutant exon 1 htt, if present, contributes to disease progression.

Animals↗
PubMed2005

Immunohistochemical localization of huntingtin-associated protein 1 in endocrine system of the rat.

Huntingtin-associated protein 1 (HAP1) was originally found to be localized in neurons and is thought to play an important role in neuronal vesicular trafficking and/or organelle transport. Based on functional similarity between neuron and endocrine cell in vesicular trafficking, we examined the expression and localization of HAP1 in the rat endocrine system using immunohistochemistry. HAP1-immunoreactive cells are widely distributed in the anterior lobe of the pituitary, scattered in the wall of the thyroid follicles, or clustered in the interfollicular space of the thyroid gland, exclusively but diffusely distributed in the medullae of adrenal glands, and selectively located in the pancreas islets. HAP1-containing cells were also found in the mucosa of stomach and small intestine with a distributive pattern similar to that of gastrointestinal endocrine cells. However, no HAP1-immunoreactive cell was found in the cortex of the adrenal gland, the testis, and the ovary. In the posterior lobe of the pituitary, HAP1-immunoreactive products were not detected in the cell bodies but in many stigmoid bodies, one kind of non-membrane-bound cytoplasmic organelle with a central or eccentric electron-lucent core. HAP1-immunoreactive stigmoid bodies were also found in the cytoplasm of endocrine cells in the thyroid gland, the medullae of adrenal gland, the pancreas islets, the stomach, and small intestine. The present study demonstrates that HAP1 is selectively expressed in part of the small peptide-, protein-, and amino-acid analog and derivative-secreting endocrine cells but not in steroid hormone-secreting cells, suggesting that HAP1 is also involved in intracellular trafficking in certain types of endocrine cells.

Adrenal Medulla↗
PubMed2005

Pathological cell-cell interactions elicited by a neuropathogenic form of mutant Huntingtin contribute to cortical pathogenesis in HD mice.

Expanded polyglutamine (polyQ) proteins in Huntington's disease (HD) as well as other polyQ disorders are known to elicit a variety of intracellular toxicities, but it remains unclear whether polyQ proteins can elicit pathological cell-cell interactions which are critical to disease pathogenesis. To test this possibility, we have created conditional HD mice expressing a neuropathogenic form of mutant huntingtin (mhtt-exon1) in discrete neuronal populations. We show that mhtt aggregation is a cell-autonomous process. However, progressive motor deficits and cortical neuropathology are only observed when mhtt expression is in multiple neuronal types, including cortical interneurons, but not when mhtt expression is restricted to cortical pyramidal neurons. We further demonstrate an early deficit in cortical inhibition, suggesting that pathological interactions between interneurons and pyramidal neurons may contribute to the cortical manifestation of HD. Our study provides genetic evidence that pathological cell-cell interactions elicited by neuropathogenic forms of mhtt can critically contribute to cortical pathogenesis in a HD mouse model.

Animals↗
PubMed2005

Polyglutamine expansion of huntingtin impairs its nuclear export.

Proteins with polyglutamine (polyQ) expansions accumulate in the nucleus and affect gene expression. The mechanism by which mutant huntingtin (htt) accumulates intranuclearly is not known; wild-type htt, a 350-kDa protein of unknown function, is normally found in the cytoplasm. N-terminal fragments of mutant htt, which contain a polyQ expansion (>37 glutamines), have no conserved nuclear localization sequences or nuclear export sequences but can accumulate in the nucleus and cause neurological problems in transgenic mice. Here we report that N-terminal htt shuttles between the cytoplasm and nucleus in a Ran GTPase-independent manner. Small N-terminal htt fragments interact with the nuclear pore protein translocated promoter region (Tpr), which is involved in nuclear export. PolyQ expansion and aggregation decrease this interaction and increase the nuclear accumulation of htt. Reducing the expression of Tpr by RNA interference or deletion of ten amino acids of N-terminal htt, which are essential for the interaction of htt with Tpr, increased the nuclear accumulation of htt. These results suggest that Tpr has a role in the nuclear export of N-terminal htt and that polyQ expansion reduces this nuclear export to cause the nuclear accumulation of htt.

Amino Acid Sequence↗
PubMed2005

HAP1 and intracellular trafficking.

Huntington's disease is caused by a polyglutamine expansion in the protein huntingtin. Several studies suggest that huntingtin and its associated protein HAP1 participate in intracellular trafficking and that polyglutamine expansion affects vesicular transport. A study now provides new evidence that HAP1 is also involved in the endocytosis of membrane receptors. These studies offer insight into the normal function of HAP1 and its involvement in Huntington's disease.

Animals↗
PubMed2004

Huntingtin-protein interactions and the pathogenesis of Huntington's disease.

At least nine inherited neurodegenerative diseases share a polyglutamine expansion in their respective disease proteins. These diseases show distinct neuropathological changes, suggesting that protein environment and protein-protein interactions play an important role in the specific neuropathology. A gain of toxic function as a result of an expanded polyglutamine tract can cause the protein huntingtin to interact abnormally with a variety of proteins, resulting in the complex of neuropathological changes seen in Huntington's disease. Recent studies have identified several huntingtin-interacting proteins that might be associated with the normal function of huntingtin and/or involved in the pathology of Huntington's disease. In this article, we focus on the potential roles of huntingtin-protein interactions in the pathogenesis of Huntington's disease.

Humans↗
PubMed2004

Huntingtin and its role in neuronal degeneration.

Huntington's disease results from a polyglutamine expansion in the N-terminal region of huntingtin (htt). This abnormality causes protein aggregation and leads to neurotoxicity. Despite its widespread expression in the brain and body, mutant htt causes selective neurodegeneration in Huntington's disease patient brains. However, Huntington's disease mouse models expressing mutant htt do not have obvious neurodegeneration despite significant neurological symptoms. Most Huntington's disease mouse models display the accumulation of toxic N-terminal mutant htt fragments in both the nucleus and neuronal processes, suggesting that these subcellular sites are hotspots for the early neuropathology of Huntington's disease. Intranuclear htt affects gene expression and may cause neuronal dysfunction. Mutant htt in neuronal processes affects axonal transport and induces degeneration, and these effects may be more relevant to the selective neurodegeneration in Huntington's disease. Growing evidence has also suggested that mutant htt mediates multiple pathological pathways. This review discusses the early pathological changes identified in Huntington's disease cellular and animal models. These changes may be the causes of neurode-generation.

Animals↗
PubMed2003

Huntingtin forms toxic NH2-terminal fragment complexes that are promoted by the age-dependent decrease in proteasome activity.

Although NH2-terminal mutant huntingtin (htt) fragments cause neurological disorders in Huntington's disease (HD), it is unclear how toxic htt fragments are generated and contribute to the disease process. Here, we report that complex NH2-terminal mutant htt fragments smaller than the first 508 amino acids were generated in htt-transfected cells and HD knockin mouse brains. These fragments constituted neuronal nuclear inclusions and appeared before neurological symptoms. The accumulation and aggregation of these htt fragments were associated with an age-dependent decrease in proteasome activity and were promoted by inhibition of proteasome activity. These results suggest that decreased proteasome activity contributes to late onset htt toxicity and that restoring the ability to remove NH2-terminal fragments will provide a more effective therapy for HD than inhibiting their production.

Animals↗
PubMed2003

Abnormal association of mutant huntingtin with synaptic vesicles inhibits glutamate release.

In Huntington disease (HD), polyglutamine expansion causes the disease protein huntingtin to aggregate and accumulate in the nucleus and cytoplasm. The cytoplasmic huntingtin aggregates are found in axonal terminals and electrophysiological studies show that mutant huntingtin affects synaptic neurotransmission. However, the biochemical basis for huntingtin-mediated synaptic dysfunction is unclear. Using electron microscopy on sections of HD mouse brains, we found that axonal terminals containing huntingtin aggregates often had fewer synaptic vesicles than did normal axonal terminals. Subcellular fractionation and electron microscopy revealed that mutant huntingtin is co-localized with huntingtin-associated protein-1 (HAP1) in axonal terminals in the brains of HD transgenic mice. Mutant huntingtin binds more tightly to synaptic vesicles than does normal huntingtin, and it decreases the association of HAP1 with synaptic vesicles in HD mouse brains. Brain slices from HD transgenic mice that had axonal aggregates showed a significant decrease in [(3)H]glutamate release, suggesting that neurotransmitter release from synaptic vesicles was impaired. Taken together, these findings suggest that mutant huntingtin has an abnormal association with synaptic vesicles and this association impairs synaptic function.

Animals↗
PubMed2003

Lack of huntingtin-associated protein-1 causes neuronal death resembling hypothalamic degeneration in Huntington's disease.

Huntington's disease (HD) is caused by a polyglutamine expansion in the disease protein huntingtin. The polyglutamine expansion causes huntingtin to interact abnormally with a number of proteins. However, it is unclear whether, and how, huntingtin-associated proteins are involved in the neurodegeneration in HD. Here, we show that huntingtin-associated protein-1 (HAP1), which is involved in intracellular trafficking of epidermal growth factor receptor (EGFR), is highly expressed in the hypothalamus. Mice lacking HAP1 die after birth because of depressed feeding activity. Terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling staining and electron microscopic examination revealed the degeneration in hypothalamic regions that control feeding behavior. Hypothalamic degeneration was also observed in HD transgenic mice that have a significant loss of body weight. Inhibition of HAP1 expression decreases EGFR signaling and cell viability, whereas overexpression of HAP1 enhances this signaling activity and inhibits mutant huntingtin-mediated cytotoxicity. These results suggest that the effect of mutant huntingtin on HAP1 and EGFR signaling may contribute to the hypothalamic neurodegeneration and loss of body weight in HD.

Animals↗
PubMed2003

Mutant huntingtin causes context-dependent neurodegeneration in mice with Huntington's disease.

Huntington's disease (HD) mouse models that express N-terminal huntingtin fragments show rapid disease progression and have been used for developing therapeutics. However, light microscopy reveals no significant neurodegeneration in these mice. It remains unclear how mutant huntingtin induces neurodegeneration. Using caspase staining, terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling, and electron microscopy, we observed that N171-82Q mice, which express the first 171 aa of mutant huntingtin, displayed more degenerated neurons than did other HD mouse models. The neurodegeneration was also evidenced by increased immunostaining for glial fibrillary acidic protein and ultrastructural features of apoptosis. R6/2 mice, which express exon 1 of mutant huntingtin, showed dark, nonapoptotic neurons and degenerated mitochondria associated with mutant huntingtin. In HD repeat knock-in mice (HdhCAG150), which express full-length mutant huntingtin, degenerated cytoplasmic organelles were found in both axons and neuronal cell bodies in association with mutant huntingtin that was not labeled by an antibody to huntingtin amino acids 342-456. Transfection of cultured cells with mutant huntingtin revealed that an N-terminal huntingtin fragment (amino acids 1-208 plus a 120 glutamine repeat) caused a greater increase in caspase activity than did exon 1 huntingtin and longer huntingtin fragments. These results suggest that context-dependent neurodegeneration in HD may be mediated by different N-terminal huntingtin fragments. In addition, this study has identified neurodegenerative markers for the evaluation of therapeutic treatments in HD mouse models.

Animals↗