PubMed Health⌕ Search

Biomedical subjects

Tiansen Li

Publications and source records attributed to Tiansen Li.

At least 19 recordsLinked to original sources
PubMed2006

Molecular analysis of fibulin-5 function during de novo synthesis of elastic fibers.

Elastic fibers contribute to the structural support of tissues and to the regulation of cellular behavior. Mice deficient for the fibulin-5 gene (fbln5(-/-)) were used to further elucidate the molecular mechanism of elastic fiber assembly. Major elastic fiber components were present in the skin of fbln5(-/-) mice despite a dramatic reduction of mature elastic fibers. We found that fibulin-5 preferentially bound the monomeric form of elastin through N-terminal and C-terminal elastin-binding regions and to a preexisting matrix scaffold through calcium-binding epidermal growth factor (EGF)-like (CB-EGF) domains. We further showed that adenovirus-mediated gene transfer of fbln5 was sufficient to regenerate elastic fibers and increase elastic fiber-cell connections in vivo. A mutant fibulin-5 lacking the first 28 amino acids of the first CB-EGF domain, however, was unable to rescue elastic fiber defects. Fibulin-5 thus serves as an adaptor molecule between monomeric elastin and the matrix scaffold to aid in elastic fiber assembly. These results also support the potential use of fibulin-5 as a therapeutic agent for the treatment of elastinopathies.

Adenoviridae↗
PubMed2006

Cyclin D1-dependent kinase activity in murine development and mammary tumorigenesis.

Cyclin D1 is a multifunctional protein that activates CDK4 and CDK6, titrates Cip/Kip CDK inhibitors to increase CDK2 activity, and modulates the function of certain transcription factors. To specifically test the importance of cyclin D1-associated kinase activity, we generated "knockin" mice expressing mutant cyclin D1 deficient in activating CDK4/6. The development of several cyclin D1-dependent compartments, including mammary glands, proceeds relatively normally in these animals, demonstrating that cyclin D1-associated kinase activity is largely dispensable for development of these tissues. Strikingly, knockin mice were resistant to breast cancers initiated by ErbB-2. These results demonstrate a differential requirement for cyclin D1-CDK4/6 kinase activity in development versus tumorigenesis and strongly support cyclin D1-dependent kinase activity as a specific therapeutic target in breast cancer.

Animals↗
PubMed2006

Effects of low AIPL1 expression on phototransduction in rods.

PURPOSE: To investigate the impact of aryl hydrocarbon receptor-interacting protein-like (AIPL)-1 on photoreception in rods. METHODS: Photoresponses of mouse rods expressing lowered amounts of AIPL1 were studied by single-cell and electroretinogram (ERG) recordings. Phototransduction protein levels and enzymatic activities were determined in biochemical assays. Ca2+ dynamics were probed with a fluorescent dye. Comparisons were made to rods expressing mutant Y99C guanylate cyclase activating protein (GCAP)-1, to understand which effects arose from elevated dark levels of cGMP and Ca2+. RESULTS: Except for PDE, transduction protein levels were normal in low-AIPL1 retinas, as were guanylate cyclase (GC), rhodopsin kinase (RK), and normalized phosphodiesterase (PDE) activities. Y99C and low-AIPL1 rods were more sensitive to flashes than normal, but flash responses of low-AIPL1 rods showed an abnormal delay, reduced rate of increase, and longer recovery not present in Y99C rod responses. In addition, low-AIPL1 rods but not Y99C rods failed to reach the normal light-induced minimum in Ca2+ concentration. CONCLUSIONS: Reduced AIPL1 delayed the photoresponse, decreased its amplification constant, slowed a rate-limiting step in its recovery, and limited the light-induced decrease in Ca2+. Not all changes were attributable to decreased PDE or to elevated cGMP and Ca2+ in darkness. Therefore, AIPL1 directly or indirectly affects more than one component of phototransduction.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Failure of elastic fiber homeostasis leads to pelvic floor disorders.

Pelvic floor disorders, a group of conditions affecting adult women, include pelvic organ prolapse and urinary incontinence. Vaginal childbirth and aging are risk factors, and weakening of the pelvic support structures is a major aspect of the pathology. However, the underlying molecular mechanism remains unknown. Female reproductive organs are rich in elastic fibers that turn over slowly in most adult tissues but undergo massive remodeling in the reproductive organs through pregnancy and birth. Here we show that a failure to maintain elastic fiber homeostasis in mice causes pelvic floor disorders. Lysyl oxidase-like-1 (LOXL1), a protein essential for the postnatal deposition of elastic fibers, was highly expressed and regulated in the reproductive tract of the mouse, and its expression was diminished during aging. LOXL1 deficiency caused an inability of reproductive tissues to replenish elastic fibers after parturition, leading to pelvic organ prolapse, weakening of the vaginal wall, paraurethral pathology, and lower urinary tract dysfunction. These data demonstrate the importance of elastic fibers for maintaining structural and functional integrity of the female pelvic floor. Our findings raise the possibility that a failure of elastic fiber homeostasis, either due to genetic predisposition or advancing age, could underlie the etiology of pelvic floor dysfunction in women.

Amino Acid Oxidoreductases↗
PubMed2005

Mouse Rab23 regulates hedgehog signaling from smoothened to Gli proteins.

Sonic hedgehog (Shh) signaling is required for the growth and patterning of many tissues in vertebrate embryos, but important aspects of the Shh signal transduction pathway are poorly understood. For example, the vesicle transport protein Rab23 is a cell autonomous negative regulator of Shh signaling, but the process affected by Rab23 has not been defined. Here, we demonstrate that Rab23 acts upstream of Gli transcription factors in patterning neural cell types in the spinal cord. Double mutant analysis indicates that the primary target of Rab23 is the Gli2 activator and that Rab23 and Gli3 repressor have additive effects on patterning. Analysis of Gli3 protein suggests that Rab23 also has a role in promoting the production of Gli3 repressor. Although the membrane proteins Patched and Smoothened change subcellular localization in response to Shh, double mutant analysis demonstrates that Rab23 does not work through either Patched or Smoothened. Instead, Rab23 appears to regulate subcellular localization of essential components of the Hedgehog pathway that act downstream of Smoothened and upstream of Gli proteins.

Animals↗
PubMed2005

Rootletin interacts with C-Nap1 and may function as a physical linker between the pair of centrioles/basal bodies in cells.

Rootletin, a major structural component of the ciliary rootlet, is located at the basal bodies and centrosomes in ciliated and nonciliated cells, respectively. Here we investigated its potential role in the linkage of basal bodies/centrioles and the mechanism involved in such linkages. We show that rootletin interacts with C-Nap1, a protein restricted at the ends of centrioles and functioning in centrosome cohesion in interphase cells. Their interaction in vivo is supported by their colocalization at the basal bodies/centrioles and coordinated association with the centrioles during the cell cycle. Ultrastructural examinations demonstrate that rootletin fibers connect the basal bodies in ciliated cells and are present both at the ends of and in between the pair of centrioles in nonciliated cells. The latter finding stands in contrast with C-Nap1, which is present only at the ends of the centrioles. Transient expression of C-Nap1 fragments dissociated rootletin fibers from the centrioles, resulting in centrosome separation in interphase. Overexpression of rootletin in cells caused multinucleation, micronucleation, and irregularity of nuclear shape and size, indicative of defects in chromosome separation. These data suggest that rootletin may function as a physical linker between the pair of basal bodies/centrioles by binding to C-Nap1.

Animals↗
PubMed2005

The ciliary rootlet interacts with kinesin light chains and may provide a scaffold for kinesin-1 vesicular cargos.

The ciliary rootlet is a large striated fibrous network originating from basal bodies in ciliated cells. To explore its postulated role in intracellular transport, we investigated the interaction between kinesin light chains (KLCs) and rootletin, the structural component of ciliary rootlets. We show here that KLCs directly interact with rootletin and are located along ciliary rootlets. Their interactions are mediated by the heptad repeats of KLCs. Further studies found that these interactions tethered kinesin heavy chains along ciliary rootlets. However, the ciliary rootlet-bound kinesin-1 did not recruit microtubules or move along ciliary rootlets. Additionally, amyloid precursor protein (APP; a kinesin-1 vesicular cargo receptor) and presenilin 1 (a presumed cargo of APP/kinesin-1) were found to be enriched along the rootletin fibers, suggesting that the interaction between ciliary rootlets and kinesin-1 recruits APP and presenilin 1 along ciliary rootlets. These findings indicate that ciliary rootlets may provide a scaffold for kinesin-1 vesicular cargos and, thus, play a role in the intracellular transport in ciliated cells.

Amyloid beta-Protein Precursor↗
PubMed2005

The ciliary rootlet maintains long-term stability of sensory cilia.

The striated ciliary rootlet is a prominent cytoskeleton originating from basal bodies of ciliated cells. Although a familiar structure in cell biology, its function has remained unresolved. In this study, we carried out targeted disruption in mice of the gene for rootletin, a component of the rootlet. In the mutant, ciliated cells are devoid of rootlets. Phototransduction and ciliary beating in sensory and motile cilia initially exhibit no apparent functional deficits. However, photoreceptors degenerate over time, and mutant lungs appear prone to pathological changes consistent with insufficient mucociliary clearance. Further analyses revealed a striking fragility at the ciliary base in photoreceptors lacking rootlets. In vitro assays suggest that the rootlet is among the least dynamic of all cytoskeletons and interacts with actin filaments. Thus, a primary function of the rootlet is to provide structural support for the cilium. Inasmuch as photoreceptors elaborate an exceptionally enlarged sensory cilium, they are especially dependent on the rootlet for structural integrity and long-term survival.

Animals↗
PubMed2005

Genetic replacement of cyclin D1 function in mouse development by cyclin D2.

D cyclins (D1, D2, and D3) are components of the core cell cycle machinery in mammalian cells. It is unclear whether each of the D cyclins performs unique, tissue-specific functions or the three proteins have virtually identical functions and differ mainly in their pattern of expression. We previously generated mice lacking cyclin D1, and we observed that these animals displayed hypoplastic retinas and underdeveloped mammary glands and a presented developmental neurological abnormality. We now asked whether the specific requirement for cyclin D1 in these tissues reflected a unique pattern of D cyclin expression or the presence of specialized functions for cyclin D1 in cyclin D1-dependent compartments. We generated a knock-in strain of mice expressing cyclin D2 in place of D1. Cyclin D2 was able to drive nearly normal development of retinas and mammary glands, and it partially replaced cyclin D1's function in neurological development. We conclude that the differences between these two D cyclins lie mostly in the tissue-specific pattern of their expression. However, we propose that subtle differences between the two D cyclins do exist and they may allow D cyclins to function in a highly optimized fashion. We reason that the acquisition of multiple D cyclins may allow mammalian cells to drive optimal proliferation of a diverse array of cell types.

Animals↗
PubMed2005

A single, abbreviated RPGR-ORF15 variant reconstitutes RPGR function in vivo.

PURPOSE: The retinitis pigmentosa GTPase regulator (RPGR) is essential for the maintenance of photoreceptor viability. RPGR is expressed as constitutive and ORF15 variants because of alternative splicing. This study was designed to examine whether the retina-specific ORF15 variant alone could substantially substitute for RPGR function. A further objective was to test whether the highly repetitive purine-rich region of ORF15 could be abbreviated without ablating the function, so as to accommodate RPGR replacement genes in adenoassociated virus (AAV) vectors. METHODS: A cDNA representing RPGR-ORF15 but shortened by 654 bp in the repetitive region was placed under the control of a chicken beta-actin (CBA) hybrid promoter. The resultant construct was transfected into mouse embryonic stem cells. Clones expressing the transgene were selected and injected into mouse blastocysts. Transgenic chimeras were crossed with RPGR knockout (KO) mice. Mice expressing the transgene but null for endogenous RPGR (Tg/KO) were studied from 1 month to 18 months of age by light and electron microscopy, immunofluorescence, and electroretinography (ERG). The results were compared with those of wild-type (WT) and RPGR-null control mice. RESULTS: Transgenic RPGR-ORF15 was found in the connecting cilia of rod and cone photoreceptors, at approximately 20% of the WT level. Photoreceptor morphology, cone opsin localization, expression of GFAP (a marker for retinal degeneration) and ERGs were consistent with the transgene exerting substantial rescue of retinal degeneration due to loss of endogenous RPGR. CONCLUSIONS: RPGR-ORF15 is the functionally significant variant in photoreceptors. The length of its repetitive region can be reduced while preserving its function. The current findings should facilitate the design of gene replacement therapy for RPGR-null mutations.

Animals↗
PubMed2005

Gene replacement therapy rescues photoreceptor degeneration in a murine model of Leber congenital amaurosis lacking RPGRIP.

PURPOSE: Retinitis pigmentosa GTPase regulator (RPGR) is a photoreceptor protein anchored in the connecting cilia by an RPGR-interacting protein (RPGRIP). Loss of RPGRIP causes Leber congenital amaurosis (LCA), a severe form of photoreceptor degeneration. The current study was an investigation of whether somatic gene replacement could rescue degenerating photoreceptors in a murine model of LCA due to a defect in RPGRIP. METHODS: An RPGRIP expression cassette, driven by a mouse opsin promoter, was packaged into recombinant adeno-associated virus (AAV). The AAV vector was delivered into the right eyes of RPGRIP(-/-) mice by a single subretinal injection into the superior hemisphere. The left eyes received a saline injection as a control. Full-field electroretinograms (ERGs) were recorded from both eyes at 2, 3, 4, and 5 months after injection. After the final follow-up, retinas were analyzed by immunostaining or by light and electron microscopy. RESULTS: Delivery of the AAV vector led to RPGRIP expression and restoration of normal RPGR localization at the connecting cilia. Photoreceptor preservation was evident by a thicker cell layer and well-developed outer segments in the treated eyes. Rescue was more pronounced in the superior hemisphere coincident with the site of delivery. Functional preservation was demonstrated by ERG. CONCLUSIONS: AAV-mediated RPGRIP gene replacement preserves photoreceptor structure and function in a mouse model of LCA, despite ongoing cell loss at the time of intervention. These results indicate that gene replacement therapy may be effective in patients with LCA due to a defect in RPGRIP and suggest that further preclinical development of gene therapy for this disorder is warranted.

Animals↗
PubMed2004

AIPL1, the protein that is defective in Leber congenital amaurosis, is essential for the biosynthesis of retinal rod cGMP phosphodiesterase.

Aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) is a member of the FK-506-binding protein family expressed specifically in retinal photoreceptors. Mutations in AIPL1 cause Leber congenital amaurosis, a severe early-onset retinopathy that leads to visual impairment in infants. Here we show that knockdown of AIPL1 expression in mice also produces a retinopathy but over a more extended time course. Before any noticeable pathology, there was a reduction in the level of rod cGMP phosphodiesterase (PDE) proportional to the decrease in AIPL1 expression, whereas other photoreceptor proteins were unaffected. Consistent with less PDE in rods, flash responses had a delayed onset, a reduced gain, and a slower recovery of flash responses. We suggest that AIPL1 is a specialized chaperone required for rod PDE biosynthesis. Thus loss of AIPL1 would result in a condition that phenocopies retinal degenerations in the rd mouse and in a subgroup of human patients.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2004

Elastic fiber homeostasis requires lysyl oxidase-like 1 protein.

Elastic fibers are components of the extracellular matrix and confer resilience. Once laid down, they are thought to remain stable, except in the uterine tract where cycles of active remodeling occur. Loss of elastic fibers underlies connective tissue aging and important diseases including emphysema. Failure to maintain elastic fibers is explained by a theory of antielastase-elastase imbalance, but little is known about the role of renewal. Here we show that mice lacking the protein lysyl oxidase-like 1 (LOXL1) do not deposit normal elastic fibers in the uterine tract post partum and develop pelvic organ prolapse, enlarged airspaces of the lung, loose skin and vascular abnormalities with concomitant tropoelastin accumulation. Distinct from the prototypic lysyl oxidase (LOX), LOXL1 localizes specifically to sites of elastogenesis and interacts with fibulin-5. Thus elastin polymer deposition is a crucial aspect of elastic fiber maintenance and is dependent on LOXL1, which serves both as a cross-linking enzyme and an element of the scaffold to ensure spatially defined deposition of elastin.

Amino Acid Oxidoreductases↗
PubMed2004

Dominant, gain-of-function mutant produced by truncation of RPGR.

PURPOSE: The retinitis pigmentosa GTPase regulator (RPGR) is essential in the maintenance of photoreceptor viability. Mutations in the X-linked RPGR gene have generally been assumed to be recessive. This study was undertaken to investigate whether certain mutant RPGR alleles may act dominantly. METHODS: An RPGR transgene representing the RPGR ORF15 variant was placed under a non-tissue-specific promoter and introduced into transgenic mice. The transgene was crossed into both a wild type (WT) and an RPGR null background. Its expression was analyzed by RT-PCR, immunoblot analysis, and immunofluorescence. Photoreceptor survival was assessed by electroretinography and histology. RESULTS: The RPGR transgene transcript underwent photoreceptor-specific, alternative splicing involving the purine-rich region of the ORF15 exon, generating a shortened mRNA and a premature stop codon. This truncation mutant caused more rapid photoreceptor degeneration than that in the RPGR null (knockout) mutant. The disease course was similar, whether the transgene was coexpressed with WT RPGR or expressed alone in the RPGR null background. CONCLUSIONS: Certain truncated forms of RPGR can behave as a dominant, gain-of-function mutant. These data suggest that human RPGR mutations are not necessarily null and some may also act as dominant alleles, leading to a more severe phenotype than a null mutant.

Alternative Splicing↗
PubMed2004

FKBP8 is a negative regulator of mouse sonic hedgehog signaling in neural tissues.

Sonic hedgehog (SHH) is a secreted morphogen that regulates the patterning and growth of many tissues in the developing mouse embryo, including the central nervous system (CNS). We show that a member of the FK506-binding protein family, FKBP8, is an essential antagonist of SHH signaling in CNS development. Loss of FKBP8 causes ectopic and ligand-independent activation of the Shh pathway, leading to expansion of ventral cell fates in the posterior neural tube and suppression of eye development. Although it is expressed broadly, FKBP8 is required to antagonize SHH signaling primarily in neural tissues, suggesting that hedgehog signal transduction is subject to cell-type specific modulation during mammalian development.

Animals↗
PubMed2003

Collagen XVIII/endostatin is essential for vision and retinal pigment epithelial function.

Age-related macular degeneration (ARMD) with abnormal deposit formation under the retinal pigment epithelium (RPE) is the major cause of blindness in the Western world. basal laminar deposits are found in early ARMD and are composed of excess basement membrane material produced by the RPE. Here, we demonstrate that mice lacking the basement membrane component collagen XVIII/endostatin have massive accumulation of sub-RPE deposits with striking similarities to basal laminar deposits, abnormal RPE, and age-dependent loss of vision. The progressive attenuation of visual function results from decreased retinal rhodopsin content as a consequence of abnormal vitamin A metabolism in the RPE. In addition, aged mutant mice show photoreceptor abnormalities and increased expression of glial fibrillary acidic protein in the neural retina. Our data demonstrate that collagen XVIII/endostatin is essential for RPE function, and suggest an important role of this collagen in Bruch's membrane. Consistent with such a role, the ultrastructural organization of collagen XVIII/endostatin in basement membranes, including Bruch's membrane, shows that it is part of basement membrane molecular networks.

Aging↗
PubMed2003

The retinitis pigmentosa GTPase regulator (RPGR)- interacting protein: subserving RPGR function and participating in disk morphogenesis.

Retinitis pigmentosa is a photoreceptor degenerative disease leading to blindness in adulthood. Leber congenital amaurosis (LCA) describes a more severe condition with visual deficit in early childhood. Defects in the retinitis pigmentosa GTPase regulator (RPGR) and an RPGR-interacting protein (RPGRIP) are known causes of retinitis pigmentosa and LCA, respectively. Both proteins localize in the photoreceptor connecting cilium (CC), a thin bridge linking the cell body and the light-sensing outer segment. We show that RPGR is absent in the CC of photoreceptors lacking RPGRIP, but not vice versa. Mice lacking RPGRIP elaborate grossly oversized outer segment disks resembling a cytochalasin D-induced defect and have a more severe disease than mice lacking RPGR. Mice lacking both proteins are phenotypically indistinguishable from mice lacking RPGRIP alone. In vitro, RPGRIP forms homodimer and elongated filaments via interactions involving its coiled-coil and C-terminal domains. We conclude that RPGRIP is a stable polymer in the CC where it tethers RPGR and that RPGR depends on RPGRIP for subcellular localization and normal function. Our data suggest that RPGRIP is also required for disk morphogenesis, putatively by regulating actin cytoskeleton dynamics. The latter hypothesis may be consistent with a distant homology between the C-terminal domain of RPGRIP and an actin-fragmin kinase, predicted by fold recognition algorithms. A defect in RPGRIP encompasses loss of both functions, hence the more severe clinical manifestation as LCA.

Amino Acid Sequence↗