Biomedical subjects

Liqun Xu

Publications and source records attributed to Liqun Xu.

5 recordsLinked to original sources

PubMed2006

Phosphorylation and cleavage of presenilin-associated rhomboid-like protein (PARL) promotes changes in mitochondrial morphology.

Remodeling of mitochondria is a dynamic process coordinated by fusion and fission of the inner and outer membranes of the organelle, mediated by a set of conserved proteins. In metazoans, the molecular mechanism behind mitochondrial morphology has been recruited to govern novel functions, such as development, calcium signaling, and apoptosis, which suggests that novel mechanisms should exist to regulate the conserved membrane fusion/fission machinery. Here we show that phosphorylation and cleavage of the vertebrate-specific Pbeta domain of the mammalian presenilin-associated rhomboid-like (PARL) protease can influence mitochondrial morphology. Phosphorylation of three residues embedded in this domain, Ser-65, Thr-69, and Ser-70, impair a cleavage at position Ser(77)-Ala(78) that is required to initiate PARL-induced mitochondrial fragmentation. Our findings reveal that PARL phosphorylation and cleavage impact mitochondrial dynamics, providing a blueprint to study the molecular evolution of mitochondrial morphology.

Amino Acid Sequence↗

PubMed2005

L-type Ca2+ channel function and expression in neonatal rabbit ventricular myocytes.

L-type Ca(2+) channel-mediated, Ca(2+)-induced Ca(2+) release (CICR) is the dominant mode of excitation-contraction (E-C) coupling in the mature mammalian myocardium but is thought to be absent in the fetal and newborn mammalian myocardium. Furthermore, the characteristics and contributors of E-C coupling at the earliest developmental stages are poorly understood. In this study, we measured [(3)H](+)PN200-110 dihydropyridine binding capacity, functionality and expression of the L-type Ca(2+) channel, and cytosolic [Ca(2+)] ([Ca(2+)](i)) at various developmental stages (3, 6, 10, 20, and 56 days old) to characterize ontogenetic changes in E-C coupling. We found that 1) the whole cell L-type Ca(2+) channel peak current (I(Ca)) density increased slightly in parallel with cell growth, but the current-voltage relationship, the steady-state activation, and the maximum DHP binding and binding affinity did not exhibit significant developmental changes; 2) sarcoplasmic reticulum Ca(2+) dependence of inactivation rates of L-type Ca(2+) channel and peak of I(Ca) density were only observed after 10 days of age, which temporally coincides with transverse (T)-tubule formation; 3) the relationship between [Ca(2+)](i) and voltage changed from a linear relationship at the earliest developmental stages to a "bell-shaped" relationship at the later developmental stages, presumably corresponding to a switch from reverse-mode Na/Ca exchange-dependent to I(Ca)-dependent E-C coupling; and 4) the expression of two different splice variants of Ca(V)1.2, IVS3A and IVS3B, switched from predominantly IVS3A at the earliest stages to IVS3B at the later developmental stages. Our data suggest that whereas the density of functional dihydropyridine receptors (DHPRs) increases only slightly during ontogeny, the enhancement of functional coupling between DHPR and ryanodine receptor is dramatic between the second and third weeks after birth. Furthermore, we found that the differential expression of splice variants during development temporally correlated with the appearance of I(Ca)-dependent E-C coupling and T-tubule formation.

Aging↗

PubMed2005

[Repair and reconstruction of oral and maxillofacial defect--clinical analysis of 1973 cases].

OBJECTIVE: To compare the reconstructive method of oral and maxillofacial defect with free tissue flaps. METHODS: The clinical materials were collected from 1 973 reconstructive cases between January 2000 and June 2004 and analyzed in terms of the distribution of age, gender, disease type, defect location, reconstructive method and the incidence of vascular crisis of free flaps as well as success rate of free flap respectively. SAS 6. 12 was adopted for statistical analysis. RESULTS: A total of 1973 reconstructive cases included 764 in middle age (>45 years to < or =60 years, 38.72%), 527 in old age (>60 years, 26.71%), 450 young adults (>28 years to < or =45 years, 22.81%), 187 in young age (>14 years to < or =28 years, 9.48%) and 45 children (< or =14 years, 2.28%). The ratio of male to female was 1.5 : 1. The ratio of benign to malignancy lesion was 1 : 1.94. The tongue defect accounted for 20.63%, followed by mandibular defect(17.38%), parotid defect(13.74%), buccal defect(12.72%), maxillary defect (8.16%), oral pharynx defect (7.60%), floor of mouth defect (5.68%) and others (14.09%). Vascular free flap transfers accounted for 45.82%(904), followed by axial flap(38.17%, 753), random flap (10.19%, 201), a vascularized bone graft (1.52%, 30) and others(4.30%, 85). The most frequently used flap was the forearm flap(594 cases), followed by the fibula free flap(143 cases) and the pedicled pectoralis major myocutaneous flap(369 cases); these three flaps accounted for 56.06% (1106/1973). In 47 free tissue flaps (5.20%) having vascular crisis, 30 were saved (63.83%). The success rate of total free tissue flaps was 98.19% (923/940). CONCLUSION: The majority of reconstructive cases of oral and maxillofacial defects is the middle aged and the old aged male patients with malignancy. The tongue defect accounts for about one fifth of all the cases. The vascularized free flap has a high success rate, so it is a main method for reconstruction of oral and maxillofacial defects. The forearm flap, the fibular free flap and the pedicled pectoralis major myocutaneous flap are the main management for repairing oral and maxillofacial defects.

Adolescent↗

PubMed2005

[Combined vascularized iliac osteo-musculo-cutaneous flap with zygomatic implant anchorage in reconstructing 1 case of maxillary defect].

OBJECTIVE: To reconstruct the maxillary defect by using free vascularized iliac osteo-musculo-cutaneous flap combined with immediate zygomatic implantation for early rehabilitation of maxillary contour and masticatory function. METHODS: In August 2003, the patient presented with deformity of left middle face (Brown II type defect) after subtotal maxillectomy. After hospitalization, a set of preoperative preparations were made, including spiral CT scanning, manufacture of nature size anatomical model and implantation protocol design. The maxillary defect was reconstructed with free vascularized iliac osteo-musculo-cutaneous flap combined with simultaneous insertion of one Bränemark zygomatic implant and two general implants. Six months later the prosthesis were placed. RESULTS: The vascularized osteo-musculo-cutaneous flap survived, the osseointegration was observed between bone and implant 6 months later. The contour of face and palate was satisfactory, the normal occluding relation was gained. The average masticatory force of operative side was 76.3% of the normal side. No tumor recurrence was noticed during the follow-up of 14 months. CONCLUSION: It is a reliable method for functional reconstruction of maxillary defect via vascularized iliac osteo-musculo-cutaneous flap combined with immediate zygomatic implantation.

Adult↗

PubMed2002

Ontogeny of excitation-contraction coupling in the mammalian heart.

The neonate mammalian heart is phenotypically different from the adult heart in many respects. Understanding these phenotypic differences are a fundamental component of understanding the mechanisms of congenital heart disease and its treatment. Differences in excitation-contraction (E-C) coupling of the neonatal heart from that of the adult include less reliance on intercellular sources of Ca(2+) such as that from sarcoplasmic reticulum (SR). Electron micrographs indicate that these immature cardiomyocytes lack transverse tubules and the SR is sparse. This paper focuses on the changes in the phenotype of E-C coupling during ontogeny in the mammalian heart and the molecular mechanisms underlying these changes.

Animals↗