Hutchinson-Gilford早老症的研究进展

Hutchinson-Gilford早老症（HGPS）为一种极为罕见的遗传性疾病，发生率1／8000000，特征性表现为患儿以极快速度衰老，多数死于冠脉病变引起的心肌梗死或广泛动脉粥样硬化导致的卒中，平均寿命13岁。绝大多数HGPS病例病因为LMNA基因第11个外显子发生点突变（G608G），生成的突变laminA由显性负效应造成细胞核结构和功能受损。目前该病已有几种动物模型，实验性治疗可以在体外将出泡的细胞核恢复正常。HGPS是研究衰老和心血管疾病机制的一个极好的模型。     

Urinary hyaluronic acid elevation in Hutchinson-Gilford progeria syndrome

The basic genetic defect in the Hutchinson-Gilford Progeria Syndrome (progeria), a premature aging syndrome, is unknown. To investigate possible defects in hyaluronic acid (HA) metabolism in this disease, the urinary excretion of HA was studied. Urine specimens from 11 patients with this disorder were examined for HA by a novel high performance liquid chromatography (HPLC) technique. In patients with progeria, HA excretion ranged from 169 micrograms HA/g creatinine to 1440 micrograms HA/g creatinine. In normal age-matched controls, HA excreted ranged from 0 to 77 micrograms HA/g creatinine. In all, a mean 17-fold increase in HA excretion was observed in patients with progeria when compared with age-matched normal controls. Total glycosaminoglycan (GAG) excretion was not elevated. Amongst normal controls, a modest age-related increase in HA excretion was observed. These results suggest that urinary HA levels are abnormally elevated in progeria.     

Reversible phenotype in a mouse model of Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a rare progeroid syndrome caused by mutations in the LMNA gene. Currently there is no treatment available for HGPS, but promising results from several studies using farnesyl transferase inhibitors (FTIs) on cells and animal models of HGPS have been published and a clinical trial using FTIs has been started in patients with HGPS. However, the published data from animal models treated with FTIs come from studies where the treatment was started before pronounced disease development. This study used an inducible transgenic animal model of HGPS with abnormalities of the skin and teeth. After phenotype development, the transgenic expression was turned off and a rapid improvement of the phenotype was noted, within 4 weeks of transgenic suppression. After 13 weeks, the skin was almost indistinguishable from wild-type skin. This study shows that in these tissues, expression of the progeria mutation does not cause irreversible damage and that reversal of disease phenotype is possible, which gives promise for a treatment for this disease.     

Somatic and gonadal mosaicism in Hutchinson-Gilford progeria

We have studied a patient with Hutchinson-Gilford progeria (HGP). Sequence analysis of the LMNA gene demonstrated the presence of a c.1824 C > T (p.G608G) mutation, activating a cryptic splice donor site and leading to the formation of a truncated Lamin A protein. All molecularly characterized autosomal dominant HGP cases described so far result from de novo LMNA mutations, mostly originating on the paternal allele and are often linked with advanced paternal age. However, in our patient, the mutation was transmitted by the mother who showed somatic and germline mosaicism without HGP manifestations.     

Hutchinson-Gilford progeria syndrome: report of a Libyan family and evidence of autosomal recessive inheritance

A Libyan family with the Hutchinson-Gilford progeria syndrome affecting three children of two sisters is described. The proband was ascertained because of repeated unhealing fractures. The pattern of inheritance appeared autosomal recessive.     

The truncated prelamin A in Hutchinson-Gilford progeria syndrome alters segregation of A-type and B-type lamin homopolymers

Hutchinson-Gilford progeria syndrome (HGPS) is a dominant autosomal premature aging syndrome caused by the expression of a truncated prelamin A designated progerin (Pgn). A-type and B-type lamins are intermediate filament proteins that polymerize to form the nuclear lamina network apposed to the inner nuclear membrane of vertebrate somatic cells. It is not known if in vivo both type of lamins assemble independently or co-assemble. The blebbing and disorganization of the nuclear envelope and adjacent heterochromatin in cells from patients with HGPS is a hallmark of the disease, and the ex vivo reversal of this phenotype is considered important for the development of therapeutic strategies. Here, we investigated the alterations in the lamina structure that may underlie the disorganization caused in nuclei by Pgn expression. We studied the polymerization of enhanced green fluorescent protein- and red fluorescent protein-tagged wild-type and mutated lamins in the nuclear envelope of living cells by measuring fluorescence resonance energy transfer (FRET) that occurs between the two fluorophores when tagged lamins interact. Using time domain fluorescence lifetime imaging microscopy that allows a quantitative analysis of FRET signals, we show that wild-type lamins A and B1 polymerize in distinct homopolymers that further interact in the lamina. In contrast, expressed Pgn co-assembles with lamin B1 and lamin A to form a mixed heteropolymer in which A-type and B-type lamin segregation is lost. We propose that such structural lamina alterations may be part of the primary mechanisms leading to HGPS, possibly by impairing functions specific for each lamin type such as nuclear membrane biogenesis, signal transduction, nuclear compartmentalization and gene regulation.     

Pluripotent stem cells to model Hutchinson-Gilford progeria syndrome (HGPS): Current trends and future perspectives for drug discovery

Progeria, or Hutchinson–Gilford progeria syndrome (HGPS), is a rare, fatal genetic disease characterized by an appearance of accelerated aging in children. This syndrome is typically caused by mutations in codon 608 (p.G608G) of the LMNA, leading to the production of a mutated form of lamin A precursor called progerin. In HGPS, progerin accumulates in cells causing progressive molecular defects, including nuclear shape abnormalities, chromatin disorganization, damage to DNA and delays in cell proliferation. Here we report how, over the past five years, pluripotent stem cells have provided new insights into the study of HGPS and opened new original therapeutic perspectives to treat the disease.     

Incomplete processing of mutant lamin A in Hutchinson-Gilford progeria leads to nuclear abnormalities, which are reversed by farnesyltransferase inhibition

Hutchinson-Gilford progeria syndrome (HGPS) is typically caused by mutations in codon 608 (G608G) of the LMNA gene, which activates a cryptic splice site resulting in the in-frame loss of 150 nucleotides from the lamin A message. The deleted region includes a protein cleavage site that normally removes 15 amino acids, including a CAAX box farnesylation site, from the lamin A protein. We investigated the processing of the C-terminus of the mutant protein, 'progerin', and found that it does not undergo cleavage and, indeed, remains farnesylated. The retention of the farnesyl group may have numerous consequences, as farnesyl groups increase lipophilicity and are involved in membrane association and in protein interactions, and is likely to be an important factor in the HGPS phenotype. To further investigate this, we studied the effects of farnesylation inhibition on nuclear phenotypes in cells expressing normal and mutant lamin A. Expression of a GFP-progerin fusion protein in normal fibroblasts caused a high incidence of nuclear abnormalities, as was also seen in HGPS fibroblasts, and resulted in abnormal nuclear localization of GFP-progerin in comparison with the localization pattern of GFP-lamin A. Expression of a GFP-lamin A fusion containing a mutation preventing the final cleavage step, causing the protein to remain farnesylated, displayed identical localization patterns and nuclear abnormalities as in HGPS cells and in cells expressing GFP-progerin. Exposure to a farnesyltransferase inhibitor (FTI), PD169541, caused a significant improvement in the nuclear morphology of cells expressing GFP-progerin and in HGPS cells. These results implicate the abnormal farnesylation of progerin in the cellular phenotype in HGPS cells and suggest that FTIs may represent a therapeutic option for patients with HGPS.     

Epidermal expression of the truncated prelamin A causing Hutchinson-Gilford progeria syndrome: effects on keratinocytes, hair and skin

Hutchinson-Gilford progeria syndrome (HGPS) is an accelerated aging disorder caused by point mutation in LMNA encoding A-type nuclear lamins. The mutations in LMNA activate a cryptic splice donor site, resulting in expression of a truncated, prenylated prelamin A called progerin. Expression of progerin leads to alterations in nuclear morphology, which may underlie pathology in HGPS. We generated transgenic mice expressing progerin in epidermis under control of a keratin 14 promoter. The mice had severe abnormalities in morphology of skin keratinocyte nuclei, including nuclear envelope lobulation and decreased nuclear circularity not present in transgenic mice expressing wild-type human lamin A. Primary keratinocytes isolated from these mice had a higher frequency of nuclei with abnormal shape compared to those from transgenic mice expressing wild-type human lamin A. Treatment with a farnesyltransferase inhibitor significantly improved nuclear shape abnormalities and induced the formation of intranuclear foci in the primary keratinocytes expressing progerin. Similarly, spontaneous immortalization of progerin-expressing cultured keratinocytes selected for cells with normal nuclear morphology. Despite morphological alterations in keratinocyte nuclei, mice expressing progerin in epidermis had normal hair grown and wound healing. Hair and skin thickness were normal even after crossing to Lmna null mice to reduce or eliminate expression of normal A-type lamins. Although progerin induces significant alterations in keratinocyte nuclear morphology that are reversed by inhibition of farnesyltransferasae, epidermal expression does not lead to alopecia or other skin abnormalities typically seen in human subjects with HGPS.     

FDA approval summary for lonafarnib (Zokinvy) for the treatment of Hutchinson-Gilford progeria syndrome and processing-deficient progeroid laminopathies

The U.S. Food and Drug Administration recently approved lonafarnib as the first treatment for Hutchinson-Gilford progeria syndrome (HGPS) and processing-deficient progeroid laminopathies. This approval was primarily based on a comparison of patients with HGPS treated with lonafarnib in 2 open-label trials with an untreated patient cohort. With up to 11 years of follow-up, it was found that the lonafarnib treated patients with HGPS had a survival benefit of 2.5 years compared with the untreated patients with HGPS. This large treatment effect on the objective endpoint of mortality using a well-matched comparator group mitigated potential sources of bias and together with other evidence, established compelling evidence of a drug effect with benefits that outweighed the risks. This approval is an example of U.S. Food and Drug Administration’s regulatory flexibility for a rare disease while ensuring that standards for drug approval are met.     

Origin,cellular expression,and cybrid transmission of mitochondrial CAP-R,PYR-IND,and OLI-R mutant phenotypes

Chloramphenicol-resistant (CAP-R) mouse and Chinese hamster lines were isolated in a single selection step in drug medium containing pyruvate. Cellular expression of the CAP-R phenotype required pyruvate— or an appropriate substitute—as a nutritional supplement. Subclone lines which were pyruvate independent (PYR-IND) arose in second-step selections at a high frequency. CAP-R PYR-IND Chinese hamster mutants could be directly isolated in single-step selections but at a very low frequency. Subclone lines (OLI-R) which were cross-resistant to oligomycin were isolated in a third selection cycle. The PYR-IND and OLI-R phenotypes were cotransmitted with the CAP-R mtDNA mutation but were expressed at the cellular level only if the number of mutant mitochondrial genomes exceeded a minimum threshold value. Analysis of a mtDNA restriction fragment alteration in one series of mutants supported this model. Threshold limits for cellular expression of mitochondrial mutant phenotypes are likely to be a general phenomenon and will constrain models of the origin and segregation of mtDNA mutations.     

A cellular assay distinguishes normal and mutant TIGR/myocilin protein.

Glaucoma is a blinding eye disease that affects approximately 70 000 000 people world-wide. Mutations in the gene TIGR / MYOC have been shown to cause the most common form of the disease, primary open angle glaucoma, in selected families. Amino acid sequence variants of the gene have been found in 2-4% of sporadic primary open angle glaucoma cases. Most variants are rare and it is often difficult to definitively distinguish between a deleterious mutation and a benign variant solely on the basis of relative frequencies in patient and control groups. The function of the TIGR/myocilin protein is unknown and an assay to functionally classify variants is lacking. We sought to develop a biochemical assay to distinguish different forms of TIGR/myocilin. We investigated the Triton X-100 detergent solubility characteristics of mutant and normal forms of the protein, expressed by transfection in cultured cells. We observed a clear difference in the behavior of the two types of TIGR/myocilin; all confirmed mutant proteins tested were substantially Triton insoluble, while normal protein and controls were completely soluble. We also tested seven ambiguous variant proteins and classified them as mutant or normal on the basis of their Triton solubility. The results in some cases validated, and in other cases contradicted, earlier classifications of these variants. To our knowledge, Triton solubility is the first example of a general difference in the properties of mutant and normal forms of TIGR/myocilin. The assay we have developed will be useful for discerning protein functional information from the location of mutations, will aid genetic counseling of individuals with TIGR/myocilin variants and may provide a clue to understanding a mechanism by which mutations in TIGR / MYOC cause glaucoma.     

RIP2对大肠杆菌的抗菌作用研究

目的: 探讨受体相互作用蛋白2(RIP2)对人肠细胞清除大肠杆菌的作用。方法: 使用阳离子聚合物JetPei^TM介导人 RIP2 基因(pEGFP-C2-PIP2)转染人结肠癌SW480细胞株,以转染空质粒及未转染的SW480细胞株作为对照,应用RT-PCR检测外源性RIP2mRNA水平的变化、Western blotting法检测细胞RIP2蛋白的表达;并利用大肠杆菌ATCC25922感染转染和未转染的SW480细胞24 h, 用平板培养菌落计数活菌数。应用p38 MAPK通路抑制剂SB203580作用于3组细胞,计数活菌数。结果: 与对照组相比,转染RIP2组其mRNA和蛋白表达水平均有明显升高(P<0.01, P<0.05),表明RIP2表达质粒成功转染SW480细胞。转染RIP2细胞能清除胞内大肠杆菌;而阻断p38 MAPK信号通路后,RIP2清除胞内大肠杆菌的作用被阻断。结论: RIP2转染细胞可有效清除胞内大肠杆菌,这种胞内细菌的清除作用可能与p38 MAPK信号通路有关。这些结果提示RIP2在细菌感染性疾病治疗中具有广阔的临床应用前景。     

A homozygous ZMPSTE24 null mutation in combination with a heterozygous mutation in the LMNA gene causes Hutchinson-Gilford progeria syndrome (HGPS): insights into the pathophysiology of HGPS

Hutchinson-Gilford progeria syndrome (HGPS) is a rare premature aging disorder normally caused by a spontaneous heterozygous mutation in the LMNA gene that codes for the nuclear lamina protein lamin A. Several enzymes are involved in the processing of its precursor, prelamin A, to the mature lamin A. A functional knockout of one of the enzymes involved in prelamin A processing, the zinc metalloprotease ZMPSTE24, causes an even more severe disorder with early neonatal death described as restrictive dermatopathy (RD). This work describes a HGPS patient with a combined defect of a homozygous loss-of-function mutation in the ZMPSTE24 gene and a heterozygous mutation in the LMNA gene that results in a C-terminal elongation of the final lamin A. Whereas the loss of function mutation of ZMPSTE24 normally results in lethal RD, the truncation of LMNA seems to be a salvage alteration alleviating the clinical picture to the HGPS phenotype. The mutations of our patient indicate that farnesylated prelamin A is the deleterious agent leading to the HGPS phenotype, which gives further insights into the pathophysiology of the disorder.