Biomedical subjects

Wei-Hua Lee

Publications and source records attributed to Wei-Hua Lee.

8 recordsLinked to original sources

PubMed2005

Insulin-like growth factor-I protects granule neurons from apoptosis and improves ataxia in weaver mice.

Most cerebellar granule neurons in weaver mice undergo premature apoptosis during the first 3 postnatal weeks, subsequently leading to severe ataxia. The death of these granule neurons appears to result from a point mutation in the GIRK2 gene, which encodes a G protein-activated, inwardly rectifying K+ channel protein. Although the genetic defect was identified, the molecular mechanism by which the mutant K+ channel selectively attacks granule neurons in weaver mice is unclear. Before their demise, weaver granule neurons express abnormally high levels of insulin-like growth factor (IGF) binding protein 5 (IGFBP5). IGF-I is essential for the survival of cerebellar neurons during their differentiation. Because IGFBP5 has the capacity to block IGF-I activity, we hypothesized that reduced IGF-I availability resulting from excess IGFBP5 accelerates the apoptosis of weaver granule neurons. We found that, consistently with this hypothesis, exogenous IGF-I partially protected cultured weaver granule neurons from apoptosis by activating Akt and decreasing caspase-3 activity. To determine whether IGF-I protects granule neurons in vivo, we cross-bred weaver mice with transgenic mice that overexpress IGF-I in the cerebellum. The cerebellar volume was increased in weaver mice carrying the IGF-I transgene, predominantly because of an increased number of surviving granule neurons. The presence of the IGF-I transgene resulted in improved muscle strength and a reduction in ataxia, indicating that the surviving granule neurons are functionally integrated into the cerebellar neuronal circuitry. These results confirm our previous suggestion that a lack of IGF-I activity contributes to apoptosis of weaver granule neurons in vivo and supports IGF-I's potential therapeutic use in neurodegenerative disease.

Age Factors↗

PubMed2005

Igf-I and postnatal growth of weaver mutant mice.

IGF-I is an anabolic growth factor essential for growth and development, both as a mediator of growth hormone (GH) action and as a local stimulator of cell proliferation and differentiation. Although the importance of IGF-I in postnatal growth has been studied for several decades, its functions in pathological states are not fully understood. The weaver (wv) mutant mouse is a commonly used model for studying hereditary cerebellar ataxia and provides us with an opportunity to study the function of IGF-I in postnatal growth during neurodegeneration. In prepubertal wv mice, we found a parallel decrease in body weight and serum IGF-I. This parallel relationship was maintained in females, but not in males, as wv mice entered puberty. Interestingly, we found an increase in the levels of circulating IGF-I and hepatic mRNA preceded the catch-up of body weight of pubertal male wv mice. The increase in IGF-I levels coincided with a surge of circulating androgen at the onset of male puberty, suggesting that androgen might trigger the increase in IGF-I production in the pubertal and adult male wv mice. Overall, our results support the concept that IGF-I plays an important role in postnatal growth during and after neurodegeneration of wv mice. In addition, IGF-I's regulation of systemic growth during and after puberty is likely modulated by androgen in male wv mice.

Animals↗

PubMed2004

High K+ and IGF-1 protect cerebellar granule neurons via distinct signaling pathways.

In culture, cerebellar granule neurons die of apoptosis in serum-free media containing a physiologic level of K(+) but survive in a depolarizing concentration of K(+) or when insulin-like growth factor 1 (IGF-1) is added. Both Akt/PKB activation and caspase-3 inhibition were implicated as the underlying neuroprotective mechanisms. The duration of high K(+), however, induced survival effects that outlasted its transient activation of Akt, and granule neurons derived from caspase-3 knockout mice died to the same extent as did those from wild-type mice, suggesting that additional mechanisms are involved. To delineate these survival mechanisms, we compared the activities of two major survival pathways after high K(+)-induced depolarization or IGF-1 stimulation. Although IGF-1 promoted neuronal survival by activating its tyrosine kinase receptor, high K(+) depolarization provided the same effect by increasing the Ca(2+) influx through the L Ca(2+) channel. Moreover, high K(+)-induced depolarization resulted in sustained activation of MAP kinase, whereas IGF-1 activated Akt in 4 hr. Inhibition of MEK (MAP kinase kinase) by either PD98059 or UO126 abolished the protective effect of high K(+)-induced depolarization, but not that of IGF-1, suggesting that activation of the MAP kinase pathway is necessary for high K(+) neuroprotective effects. We demonstrated also that high K(+)-induced depolarization, but not IGF-1, increased phosphorylation of cAMP-response element-binding protein (CREB) and protein synthesis, both of which can be blocked by UO126. Overall, our findings suggested that high K(+)-induced depolarization, unlike IGF-1, promoted neuronal survival via activating MAP kinase, possibly by increasing CREB-dependent transcriptional activation of specific proteins that promote neuronal survival.

Animals↗

PubMed2004

Potential role of IGF-I in hypoxia tolerance using a rat hypoxic-ischemic model: activation of hypoxia-inducible factor 1alpha.

Hypoxia preconditioning and subsequent tolerance to hypoxia-ischemia damage is a well-known phenomenon and has significant implications in clinical medicine. In this investigation, we tested the hypothesis that the transcriptional activation of IGF-I is one of the underlying mechanisms for hypoxia-induced neuroprotection. In a rodent model of hypoxia-ischemia, hypoxia preconditioning improved neuronal survival as demonstrated by decreased hypoxia-ischemia-induced neuronal apoptosis. To study the role of IGF-I in hypoxia tolerance, we used in situ hybridization to examine IGF-I mRNA distribution on adjacent tissue sections. In cerebral cortex and hippocampus, hypoxia preconditioning resulted in an increase in neuronal IGF-I mRNA levels with or without hypoxia-ischemia. To test its direct effects, we added IGF-I to primary neuronal culture under varying oxygen concentrations. As oxygen concentration decreased, neuronal survival also decreased, which could be reversed by IGF-I, especially at the lowest oxygen concentration. Interestingly, IGF-I treatment resulted in an activation of hypoxia-inducible factor 1alpha (HIF-1alpha), a master transcription factor for hypoxia-induced metabolic adaptation. To evaluate whether IGF-I transcriptional activation correlates with HIF-1alpha activity, we studied the time course of HIF-1alpha DNA binding activity in the same rat model of hypoxia-ischemia. After hypoxia-ischemia, there was an increase in HIF-1alpha DNA binding activity in cortical tissues, with the highest increase around 24 h. Like IGF-I mRNA levels, hypoxia preconditioning increased HIF-1alpha DNA binding activity alone or with subsequent hypoxia ischemia. Overall, our results suggest that IGF-I transcriptional activation is one of the metabolic adaptive responses to hypoxia, which is likely mediated by a direct activation of HIF-1alpha.

Adaptation, Physiological↗

PubMed2004

Calcified cataractous lens.

We report a calcified cataractous lens in a 24-year-old man who had retinal degeneration in the right eye since childhood. The visual acuity had dropped to light perception. Clear corneal phacoemulsification was performed, and the shell of a 5.4 mm x 4.0 mm x 2.0 mm calcified substance was removed with a forceps using the can-opener technique. The specimen was analyzed using radiological study, histopathological examination, chemical element analysis, and transmission electron microscopy. Four years postoperatively, the patient's visual acuity was 20/200.

Adult↗

PubMed2003

Pluripotent stem cells identified in multiple murine tissues.

Pluripotential stem cells (PSCs) have been recently described in many tissues including skeletal muscle, brain, and bone marrow. However, the true nature of these cells is still unclear, and their precise definition has yet to be determined. We hypothesized that a common, rare population of PSCs with a broad tissue differentiation potential can be identified in multiple murine tissues and that these cells are capable of transdifferentiation into cells of different primordial germ layer origins in response to diverse microenvironmental cues. To examine this hypothesis, we isolated phenotypically defined cells from murine skeletal muscle and cultured these cells under different conditions tailored to promote differentiation into several cell types including myocytes. We report here that in conditions permissive for hematopoietic differentiation, muscle-derived CD45(-)Sca-1(+)c-kit(-) cells differentiated into cells expressing hematopoietic-specific mRNA; while in conditions promoting myogenic, neuronal, and adipocytic differentiation, cells morphologically typical of these cell types expressing tissue-specific markers were identified 9-14 days in culture. When CD45(-)Sca-1(+)c-kit(-) cells from muscle or bone marrow were transplanted intracerebellarly into Purkinje cell degenerative (pcd) mice, the behavior of these mice improved 28 days after transplantation relative to mice injected with vehicle alone, suggesting that these cells contributed to the appearance of functional neuronal cells that may have improved the ataxic condition characteristic of these mice. Phenotypic analysis of single cell suspensions prepared from brain, blood, and intestinal epithelium revealed the presence of CD45(-)Sca-1(+)c-kit(-) cells in varying degrees. These studies suggest that a phenotypically common, multipotent cell can be identified in different tissues and that this cell may represent a universal pluripotent stem cell residing at different levels in multiple murine tissues.

Animals↗

PubMed2002

Inhibition of insulin-like growth factor I activity contributes to the premature apoptosis of cerebellar granule neuron in weaver mutant mice: in vitro analysis.

Evidence from transgenic mice and cultured cerebellar neurons supports an important role for insulin-like growth factor I (IGF-I) in the formation of cerebellar cytoarchitecture. To understand IGF-I's function during cerebellar development, we examined the involvement of IGF-I in the premature apoptosis of granule neurons derived from the cerebella of weaver (wv) mutant mice. Before their demise, wv granule neurons increased the expression and secretion of IGFBP5 in a gene dose-dependent manner. Because IGFBP5 may interfere with the interaction of IGF-I and its receptor, the abnormally high IGFBP5 levels in wv granule neurons suggest that a lack of IGF-I activation may contribute to their premature apoptosis. This hypothesis is supported by a gene dose-dependent decrease in IGF-I receptor (IGF-IR) phosphorylation. More importantly, there is a parallel gene dose-dependent decrease in Akt activity, which was inversely correlated with the activity levels of caspase 3. On the other hand, adding IGFBP5 antibody into culture media increased the survival of wv granule neurons, whereas adding IGFBP5 decreased the survival of wild-type granule neurons. To delineate the interaction between IGF-I and IGFBP5 on wv granule neurons, we examined neuronal survival after treating with IGF-I, des(1-3) IGF-I, or IGFBP5 antibody. At the same concentration, des(1-3) IGF-I was more effective than IGF-I in promoting survival, in increasing Akt activity, and in decreasing caspase 3 activity. These results indicate that IGF-I's actions on wv granule neurons are normally inhibited by excess IGFBP5, and sufficient IGF-I receptor activation rescues wv granule neurons via stimulating the Akt signaling pathway.

Analysis of Variance↗

PubMedDate not supplied

Detection of the human telomerase RNA component by in situ hybridization in cells from body fluids.

OBJECTIVE: To apply in situ hybridization (ISH) detection of human telomerase reverse transcriptase (hTERT) mRNA expression in abnormal cells in body fluids to evaluate its usefulness in the diagnosis of malignant effusions. STUDY DESIGN: We investigated the expression of hTERT mRNA by ISH in 33 fluid samples from 30 patients, including 1 cerebrospinal fluid, 18 pleural fluids, 1 pericardial fluid, 12 peritoneal fluids and 1 bronchial washing. Comparison of the results of ISH with those of conventional cytologic evaluation was also performed. RESULTS: Cytomorphologic examination of the 33 body fluids allowed classification as malignant, suspicious, atypical and benign conditions. Among the 17 malignant conditions, there were 15 cases positive by both cytology and ISH. There were 9 discrepant cytology-ISH results in patients with various conditions, including 2 cases positive by cytology and inconclusive by ISH, 5 cases suspicious by cytology and positive by ISH, and 2 cases atypical by cytology and negative by ISH. Among the 9 benign conditions, there were 8 cases negative by both cytology and ISH and 1 case negative by cytology and positive by ISH. This test was highly sensitive (90%) and specific (91 %) and had favorable positive (95%) and negative (83%) predictive values. CONCLUSION: Expression of the hTERT mRNA component can be easily detected by ISH in malignant cells from body fluids. This method is especially useful when the abnormal cellpopulation in the fluid consists of limited numbers of suspicious cells that cannot be completely differentiated from reactive mesothelial cells and thus may help differentiate true positive cases from false negative ones. This ISH method for the detection of expression of the hTERT mRNA component may be an ancillary test for early recognition of cancer cells in body fluids and thus has potential as a diagnostic adjunct in cytopathology.

Adolescent↗