Polymorphic Structure Determination of the Macrocyclic Drug Paritaprevir by MicroED

Paritaprevir is an orally bioavailable, macrocyclic drug used for treating chronic Hepatitis C virus infection. Its structures had been elusive to the public until recently when one of the crystal forms was solved by MicroED. In this work, we report the MicroED structures of two distinct polymorphic crystal forms of paritaprevir from the same experiment. The different polymorphs show conformational changes in the macrocyclic core, as well as the cyclopropylsulfonamide and methylpyrazinamide substituents. Molecular docking shows that one of the conformations fits well into the active site pocket of the NS3/4A serine protease target, and can interact with the pocket and catalytic triad via hydrophobic interactions and hydrogen bonds. These results can provide further insight for optimization of the binding of acylsulfonamide inhibitors to the NS3/4A serine protease. In addition, this also demonstrate the opportunity of deriving different polymorphs and distinct macrocycle conformations from the same experiments using MicroED.

MicroED as a powerful tool for structure determination of macrocyclic drug compounds directly from their powder formulations

Macrocycles are important drug leads with many advantages including the ability to target flat and featureless binding sites as well as act as molecular chameleons and thereby reach intracellular targets. However, due to their complex structures and inherent flexibility, macrocycles are difficult to study structurally and there are limited structural data available. Herein, we use the cryo-EM method MicroED to determine the novel atomic structures of several macrocycles which have previously resisted structural determination. We show that structures of similar complexity can now be obtained rapidly from nanograms of material, and that different conformations of flexible compounds can be derived from the same experiment. These results will have impact on contemporary drug discovery as well as natural product exploration.

MutiLoc Nail Versus Philos Plate in Treating Proximal Humeral Fractures: A Retrospective Study Among the Alderly

Background

Proximal humeral fractures (PHFs) account for 4–5% of all fractures in the elderly. There is still a controversy among the treatments in the displaced PHFs. Our aim was to explore the clinical outcome of PHFs with the treatment of MultiLoc nail or Philos plate in the elderly patients.

Methods

A total of 82 sustained elderly patients with PHFs were finally recruited between Dec 2016 and Dec 2017. 34 patients were treated with MultiLoc nail and 48 patients were treated with Philos plate. The demographics, fracture types, blood loss, operation time, union time, postoperative complications, visual analog scores (VASs), Constant scores, American Shoulder and Elbow Scores (ASESs), and neck-shaft-angle (NSA) between the two groups were compared.

Results

No differences were observed in the demographics, fracture types, VAS, Constant scores, and ASES scores between the two groups at final follow-up. Compared with the plate group, the blood loss, operation time, and union time were significantly lower in the nail group (all P < .05). The rate of general complications was 54.17% in the plate group, which was higher than that in the nail group (26.47%, P = .01). Three patients experienced reoperation in the plate group (3/48; 6.25%), but none in the nail group. Although there were no significant differences in intraoperative NSA between the two groups, the NSA at final follow-up in the nail group was much higher than the plate group (137.55 ± 5.53°vs 134.47 ± 5.92°, P = .02).

Conclusions

Multiloc intramedullary nail showed the similar effectiveness of final VAS, final Constant scores, and ASES scores in PHFs treatment with Philos plate. However, MultiLoc nail is superior to Philos plate in blood loss, operation time, complications, reoperation rate, and the change of NSA.

A novel classification for medial malleolar fracture based on the 3-D reconstruction CT

Background

Fracture of the medial malleolus is one of the most frequent injuries treated surgically; however, the classification of the fracture has not attracted much attention and a good classification system is still lacking.

Methods

Consecutive cases of medial malleolus fractures were prospectively enrolled. Based on the 3-D reconstruction CT morphology and centered on the posterior colliculus of the medial malleolus, we classified the fractures into 4 types: type 1 with no involvement of the posterior colliculus, type 2 with partial involvement of posterior colliculus, type 3 with the entire involvement of posterior colliculus, and type 4 with the fracture line 4 vertically extended from the intercollicular groove to the comminuted fracture of the posterior malleolus. Statistical analyses were performed to evaluate the clinical significance of the classification.

Results

There were 273 cases prospectively enrolled. The distribution of the cases was type 1 of 12.1%, type 2 of 41.0%, type 3 of 30.0%, and type 4 of 16.8%. Statistics showed that the new classification had significant associations but did not totally depend on the classical ankle fracture classifications. Results showed that the new classification had implications in the severity of ankle fractures. From type 1 to type 4, the ankle joint was more and more unstable. Furthermore, comminuted medial malleolar fractures could be subdivided, and the new classification could provide useful information for surgical decision-making.

Conclusions

The novel classification was a useful system to describe the 3-D geometry of the fractured medial malleolus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02688-9.

Complications associated with hyperextension bicondylar tibial plateau fractures: a retrospective study

Background

Hyperextension bicondylar tibial plateau fracture (HBTPF) is a particular form of tibial plateau fracture which has gained increasing interest recently but were rarely documented. In this study, we reported the characteristics, clinical intervention, and therapeutic outcomes of HBTPF patients.

Methods

From May 2015 to October 2017, clinical data of consecutive patients with bicondylar tibial plateau fractures (BTPF) who underwent surgical treatment in our hospital were retrospectively studied. The patients were allocated to either the HBTPF group (study group) or the non-HBTPF group (control group) based on the radiological features, and inclusion and exclusion criteria. Demographics, characteristics of knee joint injuries, complications, and outcomes were compared between the two groups.

Results

In total, 59 patients were included in this study. Among them, 17 patients with HBTPF were identified and 42 patients were diagnosed as non-HBTPF. No differences in age, sex, cause of injury, side of injury, site of injury, nerve injury, operation time, and treatment time and incision complication between HBTPF and non-HBTPF group. The incidence rate of popliteal artery injury in HBTPF group was 29.4 %, which was significantly higher than that of non-HBTPF group. Small bone chips on the lateral film were found in 94.1 % of the patients in HBTPF group, which was significantly higher than that of non-HBTPF group. The range of motion (ROM) and hospital for special surgery (HSS) score of HBTPF group were significantly lower than those of non-HBTPF group.

Conclusions

HBTPF is a severe injury with a higher incidence rate of popliteal artery injury and worse outcomes than non-HBTPF. Small bone chips at the anterior margin of the proximal tibia on the lateral plain film might be a characteristic of HBTPF.

Clinical research of percutaneous spinal nerve posteromedial ramus destruction in treatment for chronic facet arthrogenic low back pain: a randomized trial

BACKGROUND

To investigate the clinical effect of percutaneous spinal nerve posteromedial ramus destruction in treatment for chronic facet arthrogenic low back pain.

METHODS

A total of 118 patients with chronic facet arthrogenic low back pain were enrolled in our hospital from October 2015 to October 2018 and randomly divided into two groups. Of these patients, 59 received conservative treatment as the control group while 59 patients were treated with percutaneous spinal nerve posteromedial ramus destruction as the observation group. Pain score (Visual Analogue Scale, VAS), functional score (Oswestry Disability Index, ODI), treatment score (Japanese Orthopaedic Association, JOA), life quality score (Short Form 36-item Health Survey, SF-36), and lumbar mobility (range of motion, ROM) were evaluated before and after treatment. The treatment effect between two groups was compared.

RESULTS

The VAS score and ODI score at 2, 4, and 12 weeks after treatment and last follow-up in the observation group were lower than those of the control group (P<0.05). JOA score, SF-36, and ROM were higher than those of the control group (P<0.05).

CONCLUSIONS

Percutaneous spinal nerve posteromedial ramus destruction has a significant effect in treatment for chronic facet arthrogenic low back pain, which can relieve pain, improve function, and enhance quality of life.

[Epidemiological and pathogenic features of a bacillary dysentery outbreak in a boarding school caused by Shigella sonneri]

Objective: To investigate the etiologic and epidemiologic features of an infectious diarrhea outbreak in a boarding school in Fuyang city, Anhui province. Methods: Traceability hypothesis of this study was tested according to the epidemiological characteristics of the cases. Feces, anal swabs, water samples and food residues related to the patients and chefs were collected for pathogen isolation and detection. Biochemical identification, virulence gene detection, drug susceptibility test, PFGE and multilocus sequence typing were performed. Results: The incidence rate (3.41%) of different dormitory buildings within the water supply area by shallow wells was higher than that (0.98%) of the deep wells, with statistical significance (χ(2)=17.215, P<0.001). Sixteen strains belonged to the Shigella Sonneri family were isolated from the patient's samples, and all carrying the ipaH gene. Seven strains belonged to sen and ial genes. Set1 gene that did not appear in all the 16 strains were highly resistant to ampicillin, tetracycline, compound xinnomine, cefazoline, cefotaxime, gentamicin, naphthidinic acid and streptomycin, including 9 strains to doxycycline. The pulse field pattern of the 16 strains of Shigella sonneri appeared the same, with the ST type as ST152. Conclusion: When combined data from the etiological and epidemiological investigation, it was confirmed that Shigella sonneri was the pathogen of this outbreak, and water from the shallow wells might be responsible for the source of infection.

Lipocalin-2 protects the brain during inflammatory conditions

Sepsis is a prevalent health issue that can lead to central nervous system (CNS) inflammation with long-term behavioral and cognitive alterations. Using unbiased proteomic profiling of over 100 different cytokines, we found that Lipocalin-2 (LCN2) was the most substantially elevated protein in the CNS after peripheral administration of lipopolysaccharide (LPS). To determine whether the high level of LCN2 in the CNS is protective or deleterious, we challenged Lcn2^-/- mice with peripheral LPS and determined effects on behavior and neuroinflammation. At a time corresponding to peak LCN2 induction in wild-type (WT) mice injected with LPS, Lcn2^-/- mice challenged with LPS had exacerbated levels of pro-inflammatory cytokines and exhibited significantly worsened behavioral phenotypes. To determine the extent of global inflammatory changes dependent upon LCN2, we performed an RNAseq transcriptomic analysis. Compared with WT mice injected with LPS, Lcn2^-/- mice injected with LPS had unique transcriptional profiles and significantly elevated levels of multiple pro-inflammatory molecules. Several LCN2-dependent pathways were revealed with this analysis including, cytokine and chemokine signaling, nucleotide-binding oligomerization domain-like receptor signaling and Janus kinase-signal transducer and activator of transcription signaling. These findings demonstrate that LCN2 serves as a potent protective factor in the CNS in response to systemic inflammation and may be a potential candidate for limiting sepsis-related CNS sequelae.

Efficacy and Safety of One-Stage Selective Discectomy Combined with Expansive Hemilaminectomy in the Treatment of Cervical Spondylotic Myelopathy

OBJECTIVES

We designed a novel surgical strategy named one-stage selective discectomy combined with expansive hemilaminectomy, which might theoretically reduce the postoperative complications of cervical spondylotic myelopathy (CSM). The objective of this study is to evaluate its efficacy and safety.

METHODS

Sixty-two patients with CSM were enrolled in this study. The procedure includes selective discectomy with fusion at 1 or 2 segments of maximal cord compression and expansive hemilaminectomy on the symptomatic or severe side of the body. Neurologic function was evaluated using the Japanese Orthopedics Association Score before and after surgery. Midsagittal dural sac diameter, dural sac transverse area at segments of discetomy on magnetic resonance imaging, and lordosis of the cervical spine on lateral plain film were measured. All patients were followed up for more than 1 year.

RESULTS

A total of 88 discs and 272 hemilaminas were resected from 62 patients. The Japanese Orthopedics Association Score improved from 8.7 ± 1.76 preoperatively to 13.4 ± 1.61 at 1 year follow-up (P < 0.001). The mean midsagittal dural sac diameter, dural sac area, and lordotic angle also increased from 0.45 ± 0.10 cm, 0.83 ± 0.14 cm², and 7.9 ± 2.60° to 0.81 ± 0.08 cm, 0.96 ± 0.14 cm², and 11.7 ± 3.06°, respectively (P < 0.05). No case of postoperative axial pain, C5 palsy, nonunion, or kyphosis was reported.

CONCLUSIONS

One-stage selective discectomy combined with expansive hemilaminectomy is an effective surgical approach for the treatment of CSM in patients whose neurologic function, midsagittal dura sac diameter, and dura transverse area can be improved and has few postoperative complications.

Association of follistatin-like 3 concentrations in serum and synovial fluid with the radiographic severity of knee osteoarthritis

OBJECTIVE

Follistatin-like 3 (FSTL3), a circulating glycoprotein, is correlated with obesity and inflammation, which are potential mechanisms of osteoarthritis (OA). This study aims to determine the correlation of FSTL3 concentrations in serum and synovial fluid (SF) with the radiographic severity of OA.

METHODS

This study consisted of 200 patients with knee OA and 148 healthy controls. The radiological grading of OA in the knee was performed in accordance with Kellgren-Lawrence (KL) grading system.

RESULTS

Knee OA patients had higher serum FSTL3 concentrations compared with healthy controls. Knee OA patients with KL grade 4 showed significantly elevated FSTL3 concentrations in serum and SF compared with those with KL grades 2 and 3. Moreover, knee OA patients with KL grade 3 had significantly higher FSTL3 concentrations in serum and SF compared with those with KL grade 2. FSTL3 concentrations in serum and SF of knee OA patients were significantly correlated with KL grading criteria.

CONCLUSIONS

FSTL3 concentrations in serum and SF are correlated with the radiographic severity of OA.

Low density lipoprotein receptor related protein 1 and 6 gene variants and ischaemic stroke risk

BACKGROUND AND PURPOSE

Low density lipoprotein receptor related proteins (LRPs) 1 and 6 have been implicated in cerebral ischaemia. In addition, genetic variation in LRP1 and LRP6 has been linked with various factors that are related to risk of ischaemic stroke. The aim of this study was to examine the association of LRP1 and LRP6 gene variants with risk of ischaemic stroke as part of the Ischemic Stroke Genetics Study (ISGS).

METHODS

A Caucasian series (434 stroke patients, 319 controls) and an African American series (161 stroke patients, 116 controls) were included. Fourteen LRP6 variants and three LRP1 variants were genotyped and assessed for association with ischaemic stroke.

RESULTS

In the Caucasian series, significant associations with ischaemic stroke were observed for LRP6 rs2075241 [odds ratio (OR) 0.42, P = 0.023], rs2302685 (OR 0.44, P = 0.049), rs7975614 (OR 0.07, P = 0.017), rs10492120 (OR 0.62, P = 0.036) and rs10743980 (OR 0.66, P = 0.037). Risk of ischaemic stroke was significantly lower for carriers of any of these five protective LRP6 variants (24.0% of subjects) compared to non-carriers (OR 0.57, P = 0.003). The protective association for LRP6 rs2075241 was observed at a similar magnitude across ischaemic stroke subtypes, whilst the effects of rs23022685, rs10492120 and rs10743980 were most apparent for cardioembolic and large vessel stroke. In the African American series, LRP1 rs11172113 was associated with an increased risk of stroke (OR 1.89, P = 0.006).

CONCLUSIONS

The results of our preliminary study provide evidence that LRP6 and LRP1 variants may be associated with risk of ischaemic stroke. Validation in larger studies is warranted.

Mitogen-activated protein kinase signaling pathways are involved in regulating α7 nicotinic acetylcholine receptor-mediated amyloid-β uptake in SH-SY5Y cells

Intraneuronal accumulation of beta-amyloid protein (Aβ) is an early pathological change in Alzheimer's disease (AD). Recent studies demonstrate that α7 nicotinic acetylcholine receptor (α7nAChR) binds to soluble Aβ with a high affinity. In vitro and in vivo experiments also show that Aβ activates p38 MAPK and ERK1/2 signaling pathways via the α7nAChR. Interestingly, it has been reported that p38 MAPK and ERK1/2 signaling pathways affect the regulation of receptor-mediated endocytosis. These data suggest that MAPK signaling pathways maybe involved in the regulation of α7nAChR-mediated Aβ uptake. However, the evidence for this hypothesis is lacking. In the present study, we examined whether Aβ1-42 oligomers activate MAPK signaling pathways via α7nAChR, and assessed the role of MAPK signaling pathways in the regulation of Aβ1-42 uptake by α7nAChR. We confirm that undifferentiated SH-SY5Y cells are capable of taking up extracellular Aβ1-42. The internalization of Aβ1-42 accumulates in the endosomes/lysosomes and mitochondria. MAPK signaling pathways are activated by Aβ1-42 via α7nAChR. Aβ1-42 and α7nAChR are co-localized in SH-SY5Y cells and the expression of α7nAChR involves in Aβ1-42 uptake and accumulation in SH-SY5Y cells. Our data demonstrate that Aβ1-42 induces an α7nAChR-dependent pathway that relates to the activation of p38 MAPK and ERK1/2, resulting in internalization of Aβ1-42. Our findings suggest that α7nAChR and MAPK signaling pathways play an important role in the uptake and accumulation of Aβ1-42 in SH-SY5Y cells. Blockade of α7nAChR may have a beneficial effect by limiting intracellular accumulation of amyloid in AD brain and serves a potential therapeutic target for AD.

Characterization of glucagon-like peptide 1 receptor (GLP1R) gene in chickens: functional analysis, tissue distribution, and identification of its transcript variants

Glucagon-like peptide 1 (GLP1) receptor plays a critical role in mediating the biological actions of GLP1 in mammals and fish; however, the gene structure, expression, and functionality of GLP1 receptor (GLP1R) remain largely unknown in birds. In this study, the full-length cDNA of chicken GLP1R (cGLP1R) was first cloned from brain tissue by reverse transcription PCR. The putative cGLP1R is 459 amino acids in length and shares high amino acid sequence identity with that of human (79%), rat (80%), and Xenopus (75%). Using a pGL3-CRE luciferase reporter system, we found that cGLP1R expressed in Chinese hamster ovary cells could be potently activated by cGLP1 (EC(50), 0.11 nM) but not by other structurally related peptides, indicating that cGLP1R is a functional receptor specific to cGLP1. Interestingly, in addition to identification of the transcript encoding cGLP1R of 459 amino acids, eight transcript variants, which were generated by alternative mRNA splicing and predicted to encode either C-terminally or N-terminally truncated cGLP1Rs, were also identified from chicken brain or testis. In line with this finding, multiple cGLP1R transcripts were detected to be expressed in most chicken tissues examined, including pancreas, gastrointestinal tract, and various brain regions by reverse transcription PCR. Using the dual-luciferase reporter assay system, we further found that the 5'-flanking region of cGLP1R gene displays promoter activities in cultured HepG2 and HEK293 cells, suggesting that it may control cGLP1R gene transcription in chicken tissues, including nonpancreatic tissues. Taken together, the results from the present study establish a molecular basis to investigate the roles of GLP1 in chickens.

AQP9: a novel target for bone loss induced by microgravity

The aim of current study was to elucidate whether aquaporin-9 (AQP9) expression was involved in the progression of bone loss induced by microgravity. We used the hind-limb suspension (HLS) mice model to simulate microgravity and induce bone loss. It was found that HLS exposure decreased femur bone mineral density (BMD), and enhanced femur AQP9 mRNA and protein levels. Then, the relationship between AQP9 mRNA expression and BMD was studied and it was showed that femur AQP9 mRNA level was negatively related to femur BMD in mice exposed to HLS. We sought to exam the function of AQP9 in the femur using the AQP9-null mice. It was found that AQP9 knockout attenuated bone loss and inhibited osteoclastogenesis under the condition of HLS exposure, but had no similar effect on bone under normal physiological conditions. In addition, it was found that exposure to simulated hypergravity or exercise training, main countermeasures against microgravity, reduced AQP9 mRNA and protein levels in femur of mice. Moreover, it was found that both aging and estrogen deprivation, another two risk factors of bone loss, had no significant effect on femur AQP9 expression. In conclusion, AQP9 plays an important role in the development of microgravity-induced bone loss, and may be a potential target for the prevention or management of microgravity-induced bone loss.

The maximum A posteriori approach to the inverse problem of electrocardiography

In this paper we investigate the previously proposed maximum a posteriori (MAP) approach to the problem of determining epicardial potentials from measured body surface potentials, a form of the inverse problem of electrocardiography. The MAP inverse approach uses a priori knowledge of the covariances between epicardial electrograms in its estimate of epicardial potentials. However, in practice, this information is not generally available. In this paper we examined the effectiveness of this method when the covariances are estimated using one depolarization sequence and the MAP method is used with these covariances to estimate the epicardial potentials for a different depolarization sequence.

The roles of receptor-associated protein (RAP) as a molecular chaperone for members of the LDL receptor family

Members of the LDL receptor family mediate endocytosis and signal transduction of many extracellular ligands which participate in lipoprotein metabolism, protease regulation, embryonic development, and the pathogenesis of disease (e.g., Alzheimer's disease). Structurally, these receptors share common motifs and modules that are highlighted with clusters of cysteine-rich ligand-binding repeats. Perhaps, the most significant feature that is shared by members of the LDL receptor family is the ability of a 39-kDa receptor-associated protein (RAP) to universally inhibit ligand interaction with these receptors. Under physiological conditions, RAP serves as a molecular chaperone/escort protein for these receptors to prevent premature interaction of ligands with the receptors and thereby ensures their safe passage through the secretory pathway. In addition, RAP promotes the proper folding of these receptors, a function that is likely independent from its ability to inhibit ligand binding. The molecular mechanisms underlying these functions of RAP, as well as the molecular determinants that contribute to RAP-receptor interaction will be discussed in this review. Elucidation of these mechanisms should help to clarify how a specialized chaperone promotes the biogenesis of LDL receptor family members, and may provide insights into how the expression and function of these receptors can be regulated via the expression of RAP under pathological states.

Apolipoprotein E and apolipoprotein E receptors modulate A beta-induced glial neuroinflammatory responses

Large numbers of activated glia are a common pathological feature of many neurodegenerative disorders, including Alzheimer's disease (AD). Several different stimuli, including lipopolysaccharide (LPS), dibutyryl (db)cAMP, and aged amyloid-beta 1-42 (A beta), can induce glial activation in vitro, as measured by morphological changes and the production of pro-inflammatory cytokines and oxidative stress molecules. Only A beta-induced activation is attenuated by the addition of exogenous apolipoprotein E (apoE)-containing particles. In addition, only A beta also induces an increase in the amount of endogenous apoE, the primary apolipoprotein expressed by astrocytes in the brain. The functional significance of the increase in apoE appears to be to limit the inflammatory response. Indeed, compared to wild type mice, glial cells cultured from apoE knockout mice exhibit an enhanced production of several pro-inflammatory markers in response to treatment with A beta and other activating stimuli. The mechanism for both the A beta-induced glial activation and the increase in apoE appears to involve apoE receptors, a variety of which are expressed by both neurons and glia. Experiments using receptor associated protein (RAP), an inhibitor of apoE receptors with a differential affinity for the low-density lipoprotein receptor (LDLR) and the LDLR-related protein (LRP), revealed that LRP mediates A beta-induced glial activation, while LDLR mediates the A beta-induced changes in apoE levels. In summary, both an apoE receptor agonist (apoE) and an antagonist (RAP) inhibit A beta-induced glial cell activation. Thus, apoE receptors appear to translate the presence of extracellular A beta into cellular responses, both initiating glial cell activation and limiting its scope by inducing apoE, an anti-inflammatory agent.

High affinity binding of receptor-associated protein to heparin and low density lipoprotein receptor-related protein requires similar basic amino acid sequence motifs

The 39-kDa receptor-associated protein (RAP) is a specialized chaperone for members of the low density lipoprotein receptor gene family, which also binds heparin. Previous studies have identified a triplicate repeat sequence within RAP that appears to exhibit differential functions. Here we generated a series of truncated and site-directed RAP mutants in order to define the sites within RAP that are important for interacting with heparin and low density lipoprotein receptor-related protein (LRP). We found that high affinity binding of RAP to heparin is mediated by the carboxyl-terminal repeat of RAP, whereas both the carboxyl-terminal repeat and a combination of amino and central repeats exhibit high affinity binding to LRP. Several motifs were found to mediate the binding of RAP to heparin, and each contained a cluster of basic amino acids; among them, an intact R(282)VSR(285)SR(287)EK(289) motif is required for high affinity binding of RAP to heparin, whereas two other motifs, R(203)LR(205)R(206) and R(314)ISR(317)AR(319), also contribute to this interaction. We also found that intact motifs of both R(203)LR(205)R(206) and R(282)VSR(285)SR(287)EK(289) are required for high affinity binding of RAP to LRP, with the third motif, R(314)ISR(317)AR(319), contributing little to RAP-LRP interaction. We conclude that electrostatic interactions likely contribute significantly in the binding of RAP to both heparin and LRP and that high affinity interaction with both heparin and LRP appears to require mostly overlapping sequence motifs within RAP.

The putative tumor suppressor LRP1B, a novel member of the low density lipoprotein (LDL) receptor family, exhibits both overlapping and distinct properties with the LDL receptor-related protein

The low density lipoprotein receptor-related protein-deleted in tumor (LRP1B, initially referred to as LRP-DIT) was cloned and characterized as a candidate tumor suppressor. It is a new member of the low density lipoprotein receptor gene family. Its overall domain structure and large size (approximately 600 kDa) are similar to LRP and suggest that it is a multifunctional cell surface receptor. Herein, we characterize a series of ligands for the receptor using cell lines that stably express it as a domain IV minireceptor (mLRP1B4). Ligands of LRP including receptor-associated protein, urokinase plasminogen activator, tissue-type plasminogen activator, and plasminogen activator inhibitor type-1 each demonstrate binding, internalization, and degradation via mLRP1B4. Interestingly, the kinetics of ligand endocytosis is distinctly different from that of LRP, with LRP1B exhibiting a markedly diminished internalization rate. In addition, tissue expression analysis reveals that the LRP1B gene is expressed in brain, thyroid, and salivary gland. These studies thus extend the physiological roles of members of the LDL receptor family.

Proteasome inhibitors block a late step in lysosomal transport of selected membrane but not soluble proteins

The ubiquitin-proteasome pathway acts as a regulator of the endocytosis of selected membrane proteins. Recent evidence suggests that it may also function in the intracellular trafficking of membrane proteins. In this study, several models were used to address the role of the ubiquitin-proteasome pathway in sorting of internalized proteins to the lysosome. We found that lysosomal degradation of ligands, which remain bound to their receptors within the endocytic pathway, is blocked in the presence of specific proteasome inhibitors. In contrast, a ligand that dissociates from its receptor upon endosome acidification is degraded under the same conditions. Quantitative electron microscopy showed that neither the uptake nor the overall distribution of the endocytic marker bovine serum albumin-gold is substantially altered in the presence of a proteasome inhibitor. The data suggest that the ubiquitin-proteasome pathway is involved in an endosomal sorting step of selected membrane proteins to lysosomes, thereby providing a mechanism for regulated degradation.

Differential functions of members of the low density lipoprotein receptor family suggested by their distinct endocytosis rates

The low density lipoprotein receptor (LDLR) family is composed of a class of cell surface endocytic receptors that recognize extracellular ligands and internalize them for degradation by lysosomes. In addition to LDLR, mammalian members of this family include the LDLR-related protein (LRP), the very low density lipoprotein receptor (VLDLR), the apolipoprotein E receptor-2 (apoER2), and megalin. Herein we have analyzed the endocytic functions of the cytoplasmic tails of these receptors using LRP minireceptors, its chimeric receptor constructs, and full-length VLDLR and apoER2 stably expressed in LRP-null Chinese hamster ovary cells. We find that the initial endocytosis rates mediated by different cytoplasmic tails are significantly different, with half-times of ligand internalization ranging from less than 30 s to more than 8 min. The tail of LRP mediates the highest rate of endocytosis, whereas those of the VLDLR and apoER2 exhibit least endocytosis function. Compared with the tail of LRP, the tails of the LDLR and megalin display significantly lower levels of endocytosis rates. Ligand degradation analyses strongly support differential endocytosis rates initiated by these receptors. Interestingly apoER2, which has recently been shown to mediate intracellular signal transduction, exhibited the lowest level of ligand degradation efficiency. These results thus suggest that the endocytic functions of members of the LDLR family are distinct and that certain receptors in this family may play their main roles in areas other than receptor-mediated endocytosis.

Dissection of receptor folding and ligand-binding property with functional minireceptors of LDL receptor-related protein

The LDL receptor-related protein (LRP) is a large, multifunctional endocytic receptor that binds and endocytoses a variety of structurally and functionally distinct ligands. LRP contains four putative ligand-binding domains. However, only domains II, III and IV, but not domain I, bind the receptor-associated protein (RAP), a molecular chaperone and universal antagonist for LRP. In order to dissect the function of RAP in LRP folding and to examine the ligand-binding properties of LRP, we generated LRP minireceptors that represent each of the four putative ligand-binding domains (termed mLRP1, mLRP2, mLRP3 and mLRP4, respectively). We found that proper folding and trafficking of mLRP2, mLRP3, mLRP4, but not mLRP1, is facilitated by coexpression of RAP. When these mLRPs were stably expressed in Chinese Hamster Ovary cells that lack the endogenous LRP, we found that each of these receptors was processed and traffics through the secretory pathway. Cell surface expression of these minireceptors was quantitatively examined by flow cytometric analyses. Using these minireceptor cell lines to map the ligand-binding domains, we found that although the majority of LRP ligands bind to both domain II and domain IV, Pseudomonas exotoxin A utilizes only domain IV for its binding to LRP. We conclude that while domains II and IV of LRP share many ligand-binding properties, each of the putative ligand-binding domains of LRP is unique in its contribution to ligand binding.

Low-density lipoprotein receptor family: endocytosis and signal transduction

The low-density lipoprotein receptor (LDLR) family is composed of a class of single transmembrane glycoproteins, generally recognized as cell surface endocytic receptors, which bind and internalize extracellular ligands for degradation by lysosomes. Structurally, members of the LDLR family share homology within their extracellular domains, which are highlighted by the presence of clusters of ligand-binding repeats. Recently, information regarding the structural and functional elements within their cytoplasmic tails has begun to emerge, which suggests that members of the LDLR family function not only in receptor-mediated endocytosis, but also in transducing signals that are important during embryonic development and the pathogenesis of Alzheimer's disease. This review focuses on recent knowledge of the structural and functional aspects of LDLR family members in endocytosis and signal transduction. The relationship of these functions to the development of the neuronal system and in the pathogenesis of Alzheimer's disease is specifically discussed.

Identification of a major cyclic AMP-dependent protein kinase A phosphorylation site within the cytoplasmic tail of the low-density lipoprotein receptor-related protein: implication for receptor-mediated endocytosis

The low-density lipoprotein (LDL) receptor-related protein (LRP) is a multiligand endocytic receptor that belongs to the LDL receptor family. Recently, studies have revealed new roles of LDL receptor family members as transducers of extracellular signals. Our previous studies have demonstrated LRP phosphorylation within its cytoplasmic tail, but the nature of LRP phosphorylation and its potential function was unknown. In the present study using both in vivo and in vitro analysis, we found that LRP phosphorylation is mediated by the cAMP-dependent protein kinase A (PKA). Using site-directed mutagenesis and LRP minireceptor constructs, we further identified the predominant LRP phosphorylation site at serine 76 of its cytoplasmic tail. Finally, we demonstrated that mutations of serine 76, which abolish LRP phosphorylation by PKA, result in a decrease in the initial endocytosis rate of LRP and a lower efficiency in delivery of ligand for degradation. Thus, the role of PKA phosphorylation of LRP in receptor-mediated endocytosis may provide a mechanism by which the endocytic function of LRP can be regulated by external signals.

Uptake of HIV-1 tat protein mediated by low-density lipoprotein receptor-related protein disrupts the neuronal metabolic balance of the receptor ligands

Neurological disorders develop in most people infected with human immunodeficiency virus type 1 (HIV-1). However, the underlying mechanisms remain largely unknown. Here we report that binding of HIV-1 transactivator (Tat) protein to low-density lipoprotein receptor-related protein (LRP) promoted efficient uptake of Tat into neurons. LRP-mediated uptake of Tat was followed by translocation to the neuronal nucleus. Furthermore, the binding of Tat to LRP resulted in substantial inhibition of neuronal binding, uptake and degradation of physiological ligands for LRP, including alpha2-macroglobulin, apolipoprotein E4, amyloid precursor protein and amyloid beta-protein. In a model of macaques infected with a chimeric strain of simian-human immunodeficiency virus, increased staining of amyloid precursor protein was associated with Tat expression in the brains of simian-human immunodeficiency virus-infected macaques with encephalitis. These results indicate that HIV-1 Tat may mediate HIV-1-induced neuropathology through a pathway involving disruption of the metabolic balance of LRP ligands and direct activation of neuronal genes.

Apolipoprotein E receptors mediate the effects of beta-amyloid on astrocyte cultures

We have previously shown that beta-amyloid (Abeta) induces astrocyte activation in vitro and that this reaction is attenuated by the addition of exogenous apolipoprotein E (apoE)-containing particles. However, the effects of Abeta on endogenous apoE and apoJ levels and the potential role of apoE receptors in astrocyte activation have not been addressed. Three activating stimuli (lipopolysaccharide, dibutyryl cAMP, and aged Abeta 1-42) were used to induce activation of rat astrocyte cultures, as assessed by changes in morphology and an increase in interleukin-1beta. However, only Abeta also induced approximately 50% reduction in the amount of released apoE and apoJ and an 8-fold increase in the levels of cell-associated apoE and apoJ. Experiments using two concentrations of receptor-associated protein, an inhibitor of apoE receptors with a differential affinity for the low density lipoprotein receptor (LDLR) and the LDLR-related protein (LRP), suggest that LRP mediates Abeta-induced astrocyte activation, whereas LDLR mediates the Abeta-induced changes in apoE levels. Receptor-associated protein had no effect on apoJ levels or on activation by either dibutyryl cAMP or lipopolysaccharide. These data suggest that apoE receptors translate the presence of extracellular Abeta into cellular responses, both initiating and modulating the inflammatory response induced by Abeta.

Influence of the nasal mucociliary system on intranasal drug administration

OBJECTIVE

To study the influence of the nasal mucociliary system on intranasal drug administration and ways of reducing its influence on nasal absorption.

METHODS

Rabbit nasopharynx was closed to stop mucociliary function in one group. In the other group, rabbits maintained their mucociliary function. Both groups were given a nasal drip of gentamycin and the serum levels were measured from 0 to 180 minutes after drug administration. To reduce the undesirable effects of the nasal mucociliary system, acetylcysteine was mixed into the gentamycin drops. In addition, nasal nebulization was evaluated in human volunteers as a means of increasing absorption of the drug in the non-ciliary area of the nasal cavity.

RESULTS

Nasal mucociliary function reduced intranasal absorption of drug and made the highest absorbing rate and area under the curve (AUC) decrease by 25.1% and 18.2%, respectively. Both the nasal drip containing acetylcysteine and the nebulizer could promote drug absorption in the nasal mucosa. The former made the highest intranasal absorption and AUC increase by 18.0% and 10.7%, respectively. The latter made the absorption increase 1.5-1.6 times.

CONCLUSION

The mucociliary system can decrease intranasal drug absorption. Application of acetylcysteine or the use of nebulizer can increase drug absorption.

The YXXL motif, but not the two NPXY motifs, serves as the dominant endocytosis signal for low density lipoprotein receptor-related protein

All members of the low density lipoprotein (LDL) receptor family contain at least one copy of the NPXY sequence within their cytoplasmic tails. For the LDL receptor, it has been demonstrated that the NPXY motif serves as a signal for rapid endocytosis through coated pits. Thus, it is generally believed that the NPXY sequences function as endocytosis signals for all the LDL receptor family members. The primary aim of this study is to define the endocytosis signal(s) within the cytoplasmic tail of LDL receptor-related protein (LRP). By using LRP minireceptors, which mimic the function and trafficking of full-length endogenous LRP, we demonstrate that the YXXL motif, but not the two NPXY motifs, serves as the dominant signal for LRP endocytosis. We also found that the distal di-leucine motif within the LRP tail contributes to its endocytosis, and its function is independent of the YXXL motif. Although the proximal NPXY motif and the proximal di-leucine motif each play a limited role in LRP endocytosis in the context of the full-length tail, these motifs were functional within the truncated receptor tail. In addition, we show that LRP minireceptor mutants defective in endocytosis signal(s) accumulate at the cell surface and are less efficient in delivery of ligand for degradation.

Expression of alpha(2)-macroglobulin receptor/low density lipoprotein receptor-related protein (LRP) in rat microglial cells

Low density lipoprotein receptor-related protein (LRP) participates in the uptake and degradation of several ligands implicated in neuronal pathophysiology including apolipoprotein E (apoE), activated alpha(2) -macroglobulin (alpha(2)M*) and beta-amyloid precursor protein (APP). The receptor is expressed in a variety of tissues. In the brain LRP is present in pyramidal-type neurons in cortical and hippocampal regions and in astrocytes that are activated as a result of injury or neoplasmic transformation. As LRP is expressed in the monocyte/macrophage cell system, we were interested in examining whether LRP is expressed in microglia. We isolated glial cells from the brain of neonatal rats and LRP was immunodetected both in microglial cells and in astrocytes expressing glial fibrillar acidic protein (GFAP). Microglial cells were able to bind and internalize LRP-specific ligand, alpha(2)M*. The internalization was inhibitable by RAP, with a Kd of 1.7 nM. The expression of LRP was up-regulated by dexamethasone, and down-regulated by lipopolysaccharide (LPS), gamma interferon (IFN-gamma) or a combination of both. LRP was less sensitive to dexamethasone in activated astrocytes than in microglia. We provided the first analysis of LRP expression and regulation in microglia. Our results open the possibility that microglial cells could be related to the participation of LRP and its ligands in different pathophysiological states in brain.

Role of rap in the biogenesis of lipoprotein receptors

The LDL receptor gene family is composed of several endocytic receptors that share structural homology and function in cellular uptake of various ligands including lipoprotein particles. The complex structure of these lipoprotein receptors is highlighted by the presence of clusters of cysteine-rich ligand-binding repeats. An important feature that is shared by all these receptors is the inhibition of ligand interaction by a 39-kDa receptor-associated protein (RAP). Recent studies have shown that under physiological conditions RAP serves as a molecular chaperone to assist the folding of lipoprotein receptors and their safe passage through the secretory pathway. Several non-exclusive models have been proposed regarding the molecular mechanisms of RAP function as an antagonist for ligand interaction with the receptors and as a molecular chaperone within the early secretory pathway. Elucidation of these mechanisms may provide insights into how biogenesis of lipoprotein receptors can be regulated via the expression of RAP under physiological and pathological conditions.

Lipoproteins in the central nervous system

Although the synthesis and metabolism of plasma lipoproteins are well characterized, little is known about lipid delivery and clearance within the central nervous system (CNS). Our work has focused on characterizing the lipoprotein particles present in the cerebrospinal fluid (CSF) and the nascent particles secreted by astrocytes. In addition to carrying lipids, we have found that beta-amyloid (A beta) associates with lipoproteins, including the discoidal particles secreted by cultured astrocytes and the spherical lipoproteins found in CSF. We believe that association with lipoproteins provides a means of transport and clearance for A beta. This process may be further influenced by an interaction between A beta and apoprotein E (apoE), the primary protein component of CNS lipoproteins. Specifically, we have investigated the formation and physiologic relevance of a SDS-stable complex between apoE and A beta. In biochemical assays, native apoE2 and E3 (associated with lipid particles) form an SDS-stable complex with A beta that is 20-fold more abundant than the apoE4:A beta complex. In cell culture, native apoE3 but not E4 prevents A beta-induced neurotoxicity by a mechanism dependent on cell surface apoE receptors. In addition, apoE and the inhibition of apoE receptors prevent A beta-induced astrocyte activation. Therefore, we hypothesize that the protection from A beta-induced neurotoxicity afforded by apoE3 may result from clearance of the peptide by SDS-stable apoE3:A beta complex formation and uptake by apoE receptors.

Role of tissue plasminogen activator receptor LRP in hippocampal long-term potentiation

The low-density lipoprotein (LDL) receptor-related protein (LRP) is a multifunctional endocytic receptor that is expressed abundantly in neurons of the CNS. Both LRP and several of its ligands, including tissue plasminogen activator (tPA), apolipoprotein E/lipoproteins, alpha(2)-macroglobulin, and the beta-amyloid precursor protein, have been implicated in various neuronal functions and in the pathogenesis of Alzheimer's disease. It has been reported that induction of tPA expression may contribute to activity-dependent synaptic plasticity in the hippocampus and cerebellum. In addition, long-term potentiation (LTP) is significantly decreased in mice lacking tPA. Here we demonstrate that tPA receptor LRP is abundantly expressed in hippocampal neurons and participates in hippocampal LTP. Perfusion of hippocampal slices with receptor-associated protein (RAP), an antagonist for ligand interactions with LRP, significantly reduced late-phase LTP (L-LTP). In addition, RAP also blocked the enhancing effect of synaptic potentiation by exogenous tPA in hippocampal slices prepared from tPA knock-out mice. Metabolic labeling and ligand binding analyses showed that both tPA and LRP are synthesized by hippocampal neurons and that LRP is the major cell surface receptor that binds tPA. Finally, we found that tPA binding to LRP in hippocampal neurons enhances the activity of cyclic AMP-dependent protein kinase, a key molecule that is known to be involved in L-LTP. Taken together, our results demonstrate that interactions between tPA and cell surface LRP are important for hippocampal L-LTP.

The carboxyl-terminal domain of receptor-associated protein facilitates proper folding and trafficking of the very low density lipoprotein receptor by interaction with the three amino-terminal ligand-binding repeats of the receptor

The 39-kDa receptor-associated protein (RAP) is a specialized antagonist that inhibits all known ligand interactions with receptors that belong to the low density lipoprotein (LDL) receptor gene family. Recent studies have demonstrated a role for RAP as a molecular chaperone for the LDL receptor-related protein during receptor folding and trafficking within the early secretory pathway. In the present study, we investigated a potential role for RAP as a chaperone for the very low density lipoprotein (VLDL) receptor, another member of the LDL receptor gene family. Using intracellular cross-linking techniques, we found that RAP is associated with newly synthesized VLDL receptor. In the absence of RAP co-expression, newly synthesized VLDL receptor exhibited slower trafficking along the early secretory pathway, most likely due to misfolding of the receptor. The role of RAP in the folding of the VLDL receptor was further studied using an anchor-free, soluble VLDL receptor. Metabolic pulse-chase labeling experiments showed that while only 3% of the soluble VLDL receptor was folded and secreted in the absence of RAP co-expression, over 50% of the soluble receptor was secreted in the presence of RAP co-expression. The functions of RAP in VLDL receptor folding and trafficking were mediated by its carboxyl-terminal repeat but not by the amino-terminal and central repeats. Using truncated VLDL receptor constructs, we identified the RAP-binding site within the first three ligand-binding repeats of the VLDL receptor. Thus, our present study demonstrates that RAP serves as a folding and trafficking chaperone for the VLDL receptor via interactions of its carboxyl-terminal repeat with the three amino-terminal ligand-binding repeats of the VLDL receptor.

Intercellular adhesion molecule-1 and accumulation of eosinophils in nasal polyp tissue

OBJECTIVE

To investigate the relationship between intercellular adhesion molecule-1 (ICAM-1) and the accumulation of eosinophils in nasal polyp tissue to better understand the mechanism of airway eosinophilic inflammation.

METHODS

The expression of ICAM-1 and its natural ligand, lymphocyte function-associated antigen-1 (LFA-1), in normal nasal mucosa from 6 controls and in nasal polyp tissue from 19 patients with nasal polyposis were determined with immunohistochemistry. With dual immunohistochemistry and May-Griünwald Giemsa stain (MGG), the expression of LFA-1 and infiltrating eosinophils in nasal polyp tissue was observed.

RESULTS

The expression of ICAM-1 and LFA-1 was stronger in the nasal polyp tissue than in normal nasal mucosa. There was a positive relationship between the infiltration of eosinophils and the expression of LFA-1 on eosinophils.

CONCLUSION

Accumulation of eosinophils in nasal polyp tissue is associated with the counter-effect between adhesion molecules and its ligand on eosinophils.

Analysis of a novel mechanism of neuronal toxicity produced by an apolipoprotein E-derived peptide

The apolipoprotein E (apoE)-derived peptide (141-155)2 has a neurotoxic effect, implying that apoE itself could be a source of toxicity in Alzheimer's disease brain. We characterized the toxicity of this peptide on superior cervical ganglion (SCG) neurons and compared the death with the apoptotic death that occurs after nerve growth factor (NGF) deprivation in these cells. A dose of 10 microM apoE (141-155)2 resulted in the death of approximately 50% of the neurons within 24 h. Nuclear condensation and DNA fragmentation preceded the death. However, most inhibitors of NGF deprivation-induced death, including the caspase inhibitor Boc-aspartyl(O-methyl)fluoromethyl ketone and genetic deletion of bax-/-, had no effect on the toxicity. Inclusion of depolarizing levels of potassium did block the toxicity. Receptor-associated peptide (RAP), an antagonist for apoE receptors, did not protect cells in either SCG or hippocampal cultures. In addition, RAP had no effect on internalization of the apoE peptide. These data support the observation that apoE (141-155)2 is neurotoxic but suggest that the neurotoxicity is distinct from classical apoptosis or necrosis. Furthermore, these results indicate that the toxic effect may occur independently of members of the low-density lipoprotein receptor gene family.

Down-regulation of monocyte tissue factor mediated by tissue factor pathway inhibitor and the low density lipoprotein receptor-related protein

Inflammatory mediators like bacterial lipopolysaccharide induce monocytes to express tissue factor (TF), the cell-surface protein that triggers the blood clotting cascade in hemostasis and thrombotic disease. The physiologic ligand for TF is the serine protease, factor VIIa (FVIIa), and the resulting bimolecular enzyme, TF/FVIIa, can be reversibly inhibited by tissue factor pathway inhibitor (TFPI). Culturing monocytic cells in the presence of both FVIIa and TFPI caused down-regulation of TF expression via reducing its half-life. To exert this effect, FVIIa had to be competent to bind both TF and TFPI, and TFPI had to contain the C-terminal domain required for binding to other cell-surface receptors, including the low density lipoprotein receptor-related protein (LRP). TF down-regulation by FVIIa plus TFPI was abrogated by the 39-kDa receptor-associated protein, which blocks binding of all known ligands to LRP. Furthermore, treatment with FVIIa plus TFPI caused monocyte TF to colocalize with alpha-adaptin, a component of clathrin-coated pits. Thus, in addition to reversibly inhibiting TF/FVIIa catalytic activity, TFPI also mediates the permanent down-regulation of cell-surface TF in monocytic cells via LRP-dependent internalization and degradation. This represents an unusual mechanism for receptor internalization, requiring ligand-dependent bridging of one cell-surface receptor (TF) to a second cell-surface receptor (LRP), the latter being capable of clathrin-mediated internalization.

[Influence of intranasal medication on the structure of the nasal mucosa]

OBJECTIVE

To study the pathological changes and reversibility of the nasal mucosa after drug administration.

METHODS

Gentamicin and insulin were dropped into the nasal cavity of rabbits for 3, 5, 7 days to two weeks, after one and two weeks, the nasal mucosa was taken and observed under optical and electron microscopes.

RESULTS

It was found that after 3-7 days of drugs administration, damages of the nasal mucosa gradually appeared, and became most serious after one week when the epithelia in some regions detached from basement membr theane. After stopping drug application, the ciliated epithelia restored quickly and completely, goblet cells reproduced and inflammatory reaction disappeared.

CONCLUSION

The damages induced by drugs on nasal mucosa are reversible. The intranasal route of drug administration is feasible and promising.

[Floating culture of human nasal glandular cells]

OBJECTIVE

To establish a floating cultural model of human nasal glandular (HNG) cells.

METHODS

HNG cells were cultured on floating collagen gels.

RESULTS

Cultured HNG cells incubated with monoclonal antibody for cytokeratin stained positively. After two-week culture, the cells stained blue by AB-PAS staining. Transmission electron microscopy showed that the cells exhibited numerous microvilli on their surfaces and had numerous secretary granules. They were well polarized and interconnected by junctional complexes. Cultured HNG cells possessed typical characteristics of normal epithelium.

CONCLUSION

The floating cultural model of HNG was successfully established.

A system for medical consultation and education using multimodal human/machine communication

Recent developments in networking and computing have enabled collaborative biomedical engineering research by geographically separated participants. One of the most promising goals is to use these technologies to extend human intellectual capabilities in medical decision making. These emerging technologies are poised to drastically reduce healthcare cost by providing service at remote locations. This also increases diagnosis capacity since information is made available to experts at any location. In this paper, we propose a novel application of a recently developed interactive and distributed system in medical consultation and education. Our approach builds on the notion that interactive and distributive capabilities of the system are crucial for medical consultation and education. The presented application uses a multiuser, collaborative environment with multimodal human/machine communication in the dimensions of sight, sound, and touch. The experimental setup, consisting of two user stations, and the multimodal interfaces, including sight (eye-tracking), sound (automatic speech), and touch (microbeam pen), were tested and evaluated. The system uses a collaborative workspace as a common visualization space. Users communicate with the application through a fusion agent by eye-tracking, speech, and microbeam pen. The audio/video teleconferencing is also included to help the radiologists to communicate with each other simultaneously while they are working on the mammograms. The system used in this study has three software agents: a fusion agent, a conversational agent, and an analytic agent. The fusion agent interprets multimodal commands by integrating the multimodal inputs. The conversational agent answers the user's questions and detects human-related or semantic errors and notifies the user about the results of the image analysis. The analytic agent enhances the digitized images using the wavelet denoising algorithm if requested by the user. To show how well the system performs in practice, we used the system for medical consultation on mammograms. Results also show that the relevant information about the region of interest (ROI) of the mammograms chosen by the users is extracted automatically and used to enhance the mammograms.

The domain structure of human receptor-associated protein. Protease sensitivity and guanidine HCl denaturation

The 39-kDa receptor-associated protein (RAP), a specialized chaperone for endocytic receptors of the low density lipoprotein receptor gene family, is a triplicate repeat sequence (residues 1-100, 101-200, and 201-323, respectively), with the three repeats having different functional roles. The goal of the present study was to use a combination of protease sensitivity and guanidine denaturation analyses to investigate whether human RAP correspondingly contained multiple structural domains. Protease sensitivity analysis using six proteolytic enzymes of varying specificity showed that RAP has two protease-resistant regions contained within repeat 1 (residues 15-94) and repeat 3 (residues 223-323). Guanidine denaturation analysis showed that RAP has two phases in its denaturation, an early denaturation transition at 0.6 M guanidine HCl, and a broad second transition between 1.0 and 3.0 M guanidine HCl. Analysis of the denaturation of the individual repeats showed that, despite the similarity in sequence and protease sensitivity between repeats 1 and 3, repeat 1 was a stable structure, with a sharp transition midpoint at 2.4 M guanidine HCl, while repeat 3 was relatively unstable, with a transition midpoint at 0.6 M guanidine HCl. Repeat 2 had a denaturation profile almost identical to that of repeat 3. Denaturation analysis of the contiguous repeats 1 and 2 (residues 1-210) indicated that repeats 1 and 2 probably interact to form one structural domain represented by the broad transition, while repeat 3 constitutes a separate domain represented by the early transition. A two-domain model of RAP three-dimensional structure is proposed that integrates both structural and functional information, in which a helical segment from repeat 2 interacts with the known three-helix bundle of repeat 1 to form a four-helix bundle structural domain, while repeat 3 forms the other structural domain.

Ca2+ and receptor-associated protein are independently required for proper folding and disulfide bond formation of the low density lipoprotein receptor-related protein

The low density lipoprotein receptor-related protein (LRP) is a cysteine-rich, multifunctional receptor that binds and endocytoses a diverse array of ligands. Recent studies have shown that a 39-kDa receptor-associated protein (RAP) facilitates the proper folding and subsequent trafficking of LRP within the early secretory pathway. In the current study, we have examined the potential role of Ca2+ and its relationship to RAP during LRP folding. We found that depletion of Ca2+ following either ionomycin or thapsigargin treatment significantly disrupts the folding process of LRP. The misfolded LRP molecules migrate as high molecular weight aggregates under nonreducing SDS-polyacrylamide gel electrophoresis, suggesting the formation of intermolecular disulfide bonds. This misfolding is reversible because misfolded LRP can be re-folded into functional receptor molecules upon Ca2+ restoration. Using an LRP minireceptor representing the fourth ligand binding domain of LRP, we also observed significant variation in the conformation of monomeric receptor upon Ca2+ depletion. The role of Ca2+ in LRP folding is independent from that of RAP because RAP remains bound to LRP and its minireceptor following Ca2+ depletion. Furthermore, Ca2+ depletion-induced LRP misfolding occurs in RAP-deficient cells. Taken together, these results clearly demonstrate that Ca2+ and RAP independently participate in LRP folding.

RAP, a novel type of ER chaperone

Members of the low-density lipoprotein (LDL) receptor gene family play an important role in cellular uptake of various extracellular ligands. Recent studies have shown that a 39-kDa protein known as RAP (receptor-associated protein) serves as a molecular chaperone to assist the folding of certain LDL-receptor family proteins and their passage through the secretory pathway. In this review, the authors discuss our current understanding of the roles of RAP as a molecular chaperone/escort protein and present a model of how RAP might carry out these functions.

[Model of human nasal gland cells cultured in collagen gels]

OBJECTIVE

To establish a culture model of human nasal gland (HNG) cells in collagen gels.

METHOD

The HNG cells were cultured in collagen gels.

RESULTS

The HNG cells cultured in collagen gels showed 3-D outgrowth. After one week culture, the HNG cells developed ductal projections, the sections of collagen gel culture examined by light microscopy showed cross sectional area of tubules with a lumen containing secretory products. The cells contained numerous secretory granules. Electron microscopy showed 3-D cultured HNG cells forming a well defined lumen inside the tubular formation. These cells were polarized and interconnected by junctional complexes and possessed extensive microvilli along all their luminal border. Secretory products in the lumen and the cells located close to the luminary surface were intensely stained blue by AB-PAS staining. Immunohistochemical staining of cells labeled with a rabbit antiserum against human lysozyme showed 90% positivity.

CONCLUSION

These data indicated that HNG cells altered their phenotypes when cultured in vitro and changed from differentiated serous and mucous cells toward intermediate seromucous cells.

Evidence for normal aging of the septo-hippocampal cholinergic system in apoE (-/-) mice but impaired clearance of axonal degeneration products following injury

The association of the epsilon4 allele of apoE with increased risk for Alzheimer's disease (AD) and with poor clinical outcome after certain acute brain injuries has sparked interest in the neurobiology of apoE. ApoE (-/-) mice provide a tool to investigate the role of apoE in the nervous system in vivo. Since integrity of the basal forebrain cholinergic system is severely compromised in AD, with severity of dysfunction correlating with apoE4 gene dosage, the present study tested the hypothesis that apoE is required to maintain the normal integrity of basal forebrain cholinergic neurons (BFCNs). Histological and biochemical analyses of the septo-hippocampal cholinergic system were performed in apoE (-/-) mice during aging and following injury. Using unbiased quantitative methods, there was little or no evidence for defects in the septo-hippocampal cholinergic system, as assessed by p75(NTR)-immunoreactive neuron number and size in the medial septum, cholinergic fiber density in the hippocampus, and choline acetyltransferase activity in the hippocampus, cortex, and striatum in aged apoE (-/-) mice (up to 24 months of age) as compared to age-matched wild-type mice of the same strain. In addition, cholinergic neuronal survival and size following fimbria-fornix transection in apoE (-/-) mice did not differ from controls. However, following entorhinal cortex lesion, there was persistence of degeneration products in the deafferented hippocampus in apoE (-/-) mice. These data suggest that although apoE is not required for the maintenance of BFCNs in vivo, it may play a role in the clearance of cholesterol-laden neurodegeneration products following brain injury.