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Biomedical subjects

M Reina

Publications and source records attributed to M Reina.

At least 37 records · Page 2Linked to original sources
PubMed1998

Comparison of the new acceleration spectrum analysis with other time- and frequency-domain analyses of the signal-averaged electrocardiogram.

AIM: To compare four analysis techniques of the signal-averaged-electrocardiogram, including time-domain, spectral temporal mapping, spectral turbulence analysis and the new acceleration spectrum analysis. METHODS AND RESULTS: We studied 634 subjects (77 with bundle branch block) divided into three groups. Group 1 comprised 117 post-myocardial infarction patients tested for inducibility of sustained ventricular tachycardia, and which was induced in 54 of them. Group 2 comprised 407 consecutive acute myocardial infarction survivors, followed for 1 year; 29 of them had suffered major arrhythmic events: 15 were cases of sustained ventricular tachycardia, three resuscitated ventricular fibrillation and 11 sudden cardiac death. Group 3 comprised 110 control subjects. The different analysis techniques were compared by their likelihood ratio for the prediction of ventricular tachycardia inducibility (Group 1) or major arrhythmic events (Group 2). The likelihood ratios of spectral-turbulence-analysis, acceleration spectrum analysis, spectral temporal mapping and time-domain were 8.0, 3.3, 1.7, 1.3 in Group 1, and 3.8, 2.1, 1.5, 2.6, in Group 2, while the corresponding false-positive rates in Group 3 (control) were 0.9%, 10.0%, 4.5%, and 3.6%, respectively. CONCLUSION: Spectral turbulence analysis was the most accurate technique for the prediction of either ventricular tachycardia inducibility or major arrhythmic events after myocardial infarction. It also showed the highest specificity among control subjects.

Aged↗
PubMed1998

Binding and intracellular trafficking of lipoprotein lipase and triacylglycerol-rich lipoproteins by liver cells.

The cellular mechanisms and pathways by which lipoprotein lipase (LPL) enhances the binding and uptake of lipoproteins remains unknown. Confocal and immunoelectron microscopy demonstrated that primary binding of bovine LPL (bLPL) occurs at the microvilli surface of HepG2 cells and hepatocytes. Internalized bLPL was associated with endocytic vesicles and multivesicular bodies. Quantitative immunofluorescence indicated that the presence of bLPL caused a marked increase in the cell-surface binding of DiI-conjugated triacylglycerol-rich lipoproteins (DiI-TRL). Confocal microscopy showed that when DiI-TRL was incubated with bLPL at 4 degrees C, the distributions of bound LPL and DiI-TRL were totally coincident, and covered the apical surface of both HepG2 cells and hepatocytes. When incubated separately, the time-courses of the internalization of fluorescence associated with DiI-TRL and bLPL were different: DiI-TRL was quickly internalized by both HepG2 cells and hepatocytes, and reached a plateau at 30 min, whereas intracellular LPL increased continuously, but more slowly in the same period. In the presence of bLPL, DiI-TRL was internalized progressively by HepG2 and by cultured hepatocytes for up to 1 h and no saturation was reached. At this time the intensity of labeling of bLPL was lower than of DiI-TRL and a higher number of DiI spots did not colocalize with bLPL immunofluorescence, suggesting that the ligands follow a different pathway after internalization. The data suggest that when lipoprotein lipase (LPL) is associated with the lipoproteins it directs them to specific endocytic pathways. A hypothetical model of the intracellular pathways followed by triacylglycerol-rich lipoproteins and LPL after internalization is proposed.

Animals↗
PubMed1998

The carboxy-terminal region of human lipoprotein lipase is necessary for its exit from the endoplasmic reticulum.

Certain missense substitutions on the human lipase (hLPL) gene produce mutated proteins that are retained in different compartments along the secretory pathway. The purpose of the present study was to elucidate whether the C-terminal domain of the hLPL molecule could be important for secretion. We constructed by site-directed mutagenesis three carboxy-terminal mutated (F388-->Stop, K428-->Stop and K441-->Stop) hLPL cDNAs that were expressed in COS1 cells. Immunoblotting of cell extracts showed that all three constructs led to similar levels of protein. Both wild type (WT) hLPL and the truncated K441-->Stop hLPL were secreted to the extracellular medium, and presented a similar intracellular distribution pattern as shown by immunofluorescence. Neither F388-->Stop nor K428-->Stop hLPL protein was detected in cell medium. Immunofluorescence experiments showed that both truncated hLPL were retained within an intracellular compartment, which became larger. Double immunofluorescence analysis using antibodies against LPL and antiprotein disulfide isomerase as a marker showed that the truncated K428-->Stop hLPL was retained within the rough endoplasmic reticulum. This truncated protein was not found in other compartments in the secretory pathway, such as Golgi complex and lysosomes, indicating that it did not exit the endoplasmic reticulum. Further analysis of the C-terminal region of the LPL molecular model showed both that F388-->Stop and K428-->Stop hLPL truncated proteins are highly hydrophobic. As retention of secretory proteins in the rough endoplasmic reticulum is a quality control mechanism of the secretory pathway, we conclude that the C-terminal domain of hLPL is critical for correct intracellular processing of the newly synthesized protein.

DNA Mutational Analysis↗
PubMed1998

Bovine aortic endothelial cells express a variant of the very low density lipoprotein receptor that lacks the O-linked sugar domain.

The very low density lipoprotein (VLDL) receptor is a member of the low density lipoprotein supergene family of receptors in which differential splicing of mRNA has been reported. We present several lines of evidence showing that bovine aortic endothelial cells exclusively express a VLDL receptor isoform that lacks the O-linked sugar domain i) Western and receptor-associated protein (RAP) ligand blotting gave a single band of about 99 kDa in membrane extracts of bovine aortic endothelial cells (BAEC). ii) Screening of the BAEC cDNA library with the previously characterized human VLDL receptor cDNA as a probe gave several C-terminal-positive clones; all lacked the 84 nucleotides corresponding to exon 16. Polymerase chain reaction (PCR) confirmed that VLDL receptor cDNA encoding exon 16 was absent from the library. iii) Reverse transcription (RT)-PCR analysis of the BAEC mRNA using a pair of oligonucleotide primers that flank the deletion gave only one band of 136 nt. iv) Semiquantitative RT-PCR analysis showed that only the non-O-glycosylated variant was expressed in BAEC. Cell-binding studies with antibodies against the N-terminal domain showed that the BAEC VLDL receptor is present at the plasma membrane, suggesting that the non-glycosylated variant could be functional. In addition, RT-PCR performed in bovine tissues showed that the variant containing the O-linked sugar domain is preferentially expressed in heart, brain, and skeletal muscle, whereas the non-O-glycosylated spliced variant is found in all tissues analyzed. Taken together these results suggest that the differential splicing of the VLDL receptor is cell- and tissue-specific and that the functions of the receptor could depend on the cell type.

Alternative Splicing↗
PubMed1996

Expression and regulation of the lipoprotein lipase gene in human adrenal cortex.

Lipoprotein lipase (LPL), an enzyme which hydrolyzes triglycerides and participates in the catabolism of remnant lipoproteins, plays a crucial role in energy and lipid metabolism. The goal of this study was to analyze the expression and regulation of the LPL gene in human adrenals. Reverse transcriptase-polymerase chain reaction amplification and sequence analysis demonstrated the presence of LPL mRNA in fetal and adult human adrenal cortex. Furthermore, the human adrenocortical carcinoma cell line, NCI-H295, expresses LPL mRNA and protein, which is localized to the outer cellular membrane as demonstrated by immunofluorescence confocal microscopy and can be released in the medium by heparin addition. To asses whether the LPL gene is regulated by agents regulating adrenal steroidogenesis, NCI-H295 cells were treated with activators of second messenger systems. Whereas the calcium-ionophore A23187 did not affect LPL gene expression, treatment with phorbol 12-myristate 13-acetate decreased LPL mRNA levels in a time- and dose-dependent manner. This decrease after phorbol 12-myristate 13-acetate was associated with diminished heparin-releasable LPL mass and activity in the culture medium. Addition of the cAMP analog 8-Br-cAMP to NCI-H295 cells resulted in a rapid, but transient dose-dependent induction of LPL mRNA. Treatment with the protein synthesis inhibitor cycloheximide gradually induced, whereas simultaneous addition of cAMP and cycloheximide superinduced LPL mRNA levels. Nuclear run-on analysis indicated that the effects of cAMP and cycloheximide occurred at the transcriptional and post-transcriptional level, respectively. Transient co-transfection assays demonstrated that the first 230 base pairs of the proximal LPL promoter contain a cAMP-responsive element activated by protein kinase A and transcription factors belonging to the CREB/CREM family. These data indicate that LPL is expressed in human adrenal cortex and regulated in NCI-H295 adrenocortical carcinoma cells by activators of the protein kinase A and protein kinase C second messenger pathways in a manner comparable to P450scc, which catalyzes the first step in adrenal steroidogenesis. These observations suggest a role for LPL in adrenal energy and/or lipid metabolism and possibly in steroidogenesis.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

The mutation Gly142-->Glu in human lipoprotein lipase produces a missorted protein that is diverted to lysosomes.

While the molecular characterization of lipoprotein lipase (LPL) activation is progressing, the intracellular processing, transport, and secretion signals of LPL are still poorly known. The aim of this paper is to study are involvement of glycine 142 in LPL secretion and to elucidate the intracellular destination of the altered protein that remains inside the cell. We mutated the human LPL cDNA by site-directed mutagenesis in order to produce the G142e hLPL in which the glycine 142 was replaced by a glutamic acid. The wild type human LPL (WT hLPL) and the mutant G142E hLPL were expressed by transient transfection in COS1 cells. Using Western blot assays we identified a single band that had the same molecular weight for both proteins. However, Western blots of culture media did not reveal any specific band for the mutant protein, and ELISA experiments showed that the extracellular mass of the mutant LPL was only 25% of the WT protein, indicating defective secretion of the altered enzyme. Heparin increased LPL secretion in the case of the WT hLPL but did not have any stimulatory effect when acting on G142E hLPL-transfected cells. However, heparin-Sepharose chromatography revealed that both proteins presented the same heparin affinity. Metabolic labeling and radioimmunoprecipitation studies showed that both the WT and the mutant hLPL intracellular levels decreased upon chase time. Furthermore, leupeptin had a greater effect on the intracellular level of the mutant enzyme, thus indicating its higher intracellular degradation. Immunofluorescent studies using confocal microscopy indicated high colocalization of the LPL labeling and the Lamp1 lysosomal labeling in G142E hLPL-expressing cells. This result was confirmed using immunoelectron microscopy, which in addition showed gold labeling in Golgi stacks. This finding together with experiments performed with endoglycosidase H digestion of immunoprecipitated radiolabeled LPL, indicated that the mutant enzyme entered the Golgi compartment. The results reported in this paper show that the G142E hLPL is not efficiently secreted to the extracellular medium, but it is missorted to lysosomes for intracellular degradation. This finding suggests that lysosomal missorting might be a mechanism of cell quality control of secreted LPL.

Animals↗
PubMed1996

Ligand binding to heparan sulfate proteoglycans induces their aggregation and distribution along actin cytoskeleton.

Cell surface heparan sulfate proteoglycans (HSPGs) participate in molecular events that regulate cell adhesion, migration, and proliferation. The present study demonstrates that soluble heparin-binding proteins or cross-linking antibodies induce the aggregation of cell surface HSPGs and their distribution along underlying actin filaments. Immunofluorescence and confocal microscopy and immunogold and electron microscopy indicate that, in the absence of ligands, HSPGs are irregularly distributed on the fibroblast cell surface, without any apparent codistribution with the actin cytoskeleton. In the presence of ligand (lipoprotein lipase) or antibodies against heparan sulfate, HSPGs aggregate and colocalize with the actin cytoskeleton. Triton X-100 extraction and immunoelectron microscopy have demonstrated that in this condition HSPGs were clustered and associated with the actin filaments. Crosslinking experiments that use biotinylated lipoprotein lipase have revealed three major proteoglycans as binding sites at the fibroblast cell surface. These cross-linked proteoglycans appeared in the Triton X-100 insoluble fraction. Platinum/carbon replicas of the fibroblast surface incubated either with lipoprotein lipase or antiheparan sulfate showed large aggregates of HSPGs regularly distributed along cytoplasmic fibers. Quantification of the spacing between HSPGs by confocal microscopy confirmed that the nonrandom distribution of HSPG aggregates along the actin cytoskeleton was induced by ligand binding. When cells were incubated either with lipoprotein lipase or antibodies against heparan sulfate, the distance between immunofluorescence spots was uniform. In contrast, the spacing between HSPGs on fixed cells not incubated with ligand was more variable. This highly organized spatial relationship between actin and proteoglycans suggests that cortical actin filaments could organize the molecular machinery involved in signal transduction and molecular movements on the cell surface that are triggered by heparin-binding proteins.

Actin Cytoskeleton↗
PubMed1996

Lipoprotein lipase in highly vascularized structures of the eye.

Ocular tissues are highly dependent on lipid turnover and metabolism, which requires an uptake mechanism for fatty acids from lipoproteins. We studied the activity and expression of lipoprotein lipase (LPL), which catalyzes the hydrolysis of plasma triglycerides, in different ocular regions. Human and bovine eyes were dissected and various specialized anatomical areas were assayed for LPL activity, mRNA, and immunoreactivity. Variable levels of LPL activity were detected in all structures in human and bovine eyes. LPL activity was much higher in vascularized structures, such as ciliary body, iris, and retina than in avascular eye structures, such as vitreous body, lens, and cornea. In both human and bovine eyes, ciliary body contained the highest LPL lipolytic activity. LPL mRNA was detected by reverse transcription followed by polymerase chain reaction (RT-PCR) in all regions of human eyes. By RT-PCR analysis it was shown that bovine eyes contained high levels of LPL mRNA in ciliary body and iris, lower levels were found in retina, optic nerve, and lens, whereas no LPL mRNA could be found in bovine cornea. RT-PCR data, obtained in bovine eyes, agree with the results obtained by Northern blot experiments, confirming the high levels of LPL mRNA in iris and ciliary body. Immunofluorescence experiments performed on human eye samples indicated that the LPL protein is mostly distributed on the choroides, the choriocapillaris, and on the vessels of ciliary body, iris, optic nerve, and retina. The present study demonstrates that active LPL protein is synthesized, secreted, and located among microvessels in several specialized regions of the eye, and suggests that LPL could be involved in the uptake of fatty acids by the ocular tissues.

Adolescent↗
PubMed1995

The mutant Asn291-->Ser human lipoprotein lipase is associated with reduced catalytic activity and does not influence binding to heparin.

Lipoprotein lipase (LPL) plays a central role in triglyceride metabolism, regulating the catabolism of triglyceride-rich lipoprotein particles. LPL performs its hydrolytic action attached to heparan sulfate proteoglycans at the luminal surface of capillary endothelial cells. We have assessed the effect of the Asn291-->Ser (N291S) substitution found in LPL gene from a human hyperlipemic patient. Our results showed that both the wild-type (WT) and N291S hLPL expressed in COS1 cells were secreted to the extracellular medium, and presented similar intracellular distribution patterns. Furthermore, heparin-Sepharose affinity chromatography assays revealed normal heparin affinity of the N291S hLPL. In addition, both the mutant and the WT protein bound to the surface of human fibroblasts and untransfected COS1 cells. Interestingly, diminished LPL specific activity was observed in the extracellular medium from mutant expressing cells. Therefore the lack of normal LPL activity in patients harbouring such a mutation could be the cause of their hyperlipemic disorder.

Base Sequence↗
PubMed1995

The muscle-specific phosphoglycerate mutase gene is specifically expressed in testis during spermatogenesis.

Spermatogenesis is a dramatic differentiation process which involves very selective but poorly characterized gene-expression patterns. To gain insight into this process, we have investigated the expression during spermatogenesis of the genes that encode phosphoglycerate mutase, an essential glycolytic enzyme for the spermatozoa energy supply. By using cDNA and genomic probes we demonstrate the presence in testis of a mRNA corresponding to the muscle-specific phosphoglycerate mutase which shows a longer poly(A) tail. This muscle-specific gene is submitted to developmental regulation during testis maturation and begins to be expressed at postnatal day 22, when germ cells start to enter into meiosis. Northern blot and in situ hybridization experiments show that in contrast to what happens during skeletal-muscle differentiation, PGAM-M gene expression during spermatogenesis is not coupled to constitutive phosphoglycerate mutase (PGAM-B) gene repression. Thus, the muscle-specific PGAM-M gene constitutes a meiotic gene and therefore represents a very interesting model to study differential tissue-specific gene expression.

Animals↗
PubMed1995

Actin cytoskeleton of fibroblasts organizes surface proteoglycans that bind basic fibroblast growth factor and lipoprotein lipase.

Cell surface proteoglycans participate in molecular events that regulate cell adhesion, migration, and proliferation. To investigate the organization of these molecules at the cell surface, the distribution of two well-known proteoglycan ligands has been studied. These ligands, lipoprotein lipase and basic fibroblast growth factor, showed a characteristic binding pattern consisting of highly organized parallel arrays that crossed the upper surface of human skin fibroblasts. The proteoglycan nature of the binding sites was evident from their susceptibility to heparinases, and from ligand displacement by heparin. Parallel localization of the ligands and actin, and treatment of the cells with cytochalasin, showed that the binding proteoglycans are organized by the actin cytoskeleton. The ligands induced a different behaviour of the binding sites on incubation of the cells at 37 degrees C. Lipoprotein lipase produced a movement of the binding proteoglycans along the actin filaments towards the cell center. In contrast, after binding of basic fibroblast growth factor the binding proteoglycans remained spread over the cell surface and actin depolymerization was induced. Since an increasing number of ligands appear to depend on proteoglycans for their interactions with their high affinity receptors, distribution and movement of proteoglycans at the cell surface that is organized by the actin cytoskeleton could direct and enhance the encounters between the ligands and their specific receptors.

Actins↗
PubMed1995

Short-term reproducibility of time domain, spectral temporal mapping, and spectral turbulence analysis of the signal-averaged electrocardiogram in normal subjects and patients with acute myocardial infarction.

The aim of this prospective study was to compare the short-term reproducibility of the signal-averaged ECG (SAECG) with three analysis techniques, conventional time-domain analysis, spectral-temporal mapping (STM), and spectral-turbulence analysis (STA), in a large series of normal subjects and patients with acute myocardial infarction (AMI). Two consecutive SAECGs were recorded in 225 consecutive patients 10.2 +/- 2.7 days after AMI and in 85 healthy volunteers. The visual, diagnostic, and quantitative reproducibility of the three techniques was compared. Time-domain analysis was the most reproducible method, having high R2 correlations, statistically fewer inconsistent diagnostic recordings, and statistically smaller differences compared with other techniques. STM was the least reproducible, justifying caution in its current form. Although STA was significantly less reproducible than time-domain analysis, it was also significantly better than STM. Two STA parameters, spectral entropy and interslice correlation mean, showed good reproducibility, suggesting that modification of this analysis technique could be useful in risk stratification.

Aged↗
PubMed1995

Absence of N-glycosylation at asparagine 43 in human lipoprotein lipase induces its accumulation in the rough endoplasmic reticulum and alters this cellular compartment.

Lipoprotein lipase (LPL) is the enzyme responsible for the hydrolysis of plasma triglycerides from apolipoprotein C-II-containing lipoproteins at the capillary endothelium and it is synthesized in parenchymal cells of several tissues. Intracellular LPL processing is a major aspect of LPL regulation. The present study aims to determine the intracellular accumulation site of the LPL that is not glycosylated at Asn43. Human LPL (hLPL) cDNA was mutated by site-directed mutagenesis. An Ala residue was substituted for Asn at position 43 of the protein generating N43A hLPL. Wild type hLPL and the mutant hLPL were expressed in COS1 cells. Using immunofluorescence and immunoelectron microscopy we found that wild type hLPL in addition to being secreted into the medium was present in the rough endoplasmic reticulum (ER), Golgi compartments, and vesicles. Neither LPL activity nor protein was found in medium of cells expressing the mutant hLPL and all detectable protein was present exclusively in the ER identified witha specific antibody against the protein disulfide isomerase (PDI), an ER marker. In addition, the intracellular distribution of the ER of the cells that expressed the mutant protein was grossly altered. Treatment of COS1 cells with tunicamycin for 24 h had the same effect on wild type hLPL processing and edoplasmic reticulum distribution. Next, we investigated the influence of the accumulation of mutant hLPL on the intracellular transport of three other proteins that are N-glycosylated before reaching the plasma membrane: the related Bo,+ amino acid transporter (rBAT), the insulin-regulated glucose transporter (GLUT4), and the placental alkaline phosphatase (PLAP) protein. Coexpression of the mutant hLPL (but not wild type) caused the accumulation of rBAT and GLUT4 in the ER while PLAP reached the plasma membrane. Our findings demonstrate that glycosylation of Asn43 of human lipoprotein lipase in the endoplasmic reticulum is essential for its efflux from this compartment and that the retention of the non-glycosylated LPL induces morphological changes in the ER that could also affect its ability to modify the transport of other proteins.

Asparagine↗
PubMed1994

Narrow A/T-rich zones present at the distal 5'-flanking sequences of the zein genes Zc1 and Zc2 bind a unique 30 kDa HMG-like protein.

Nuclear extracts from maize endosperm were used to investigate protein-DNA interactions in the 5'-upstream region of the Zc1 and Zc2 genes. These genes encode for zeins of apparent molecular mass (MWapp) 16 and 28 kDa, respectively, which accumulate in the endosperm during seed maturation. Binding assays revealed specific binding of a nuclear protein to three A/T-rich elements, 0.9-1.0 kbp upstream from the initiation codon. One of these elements (41 bp, 88% A/T), present in Zc1, contained a 13 nucleotide duplication. The other two (28 bp, 86% A/T; 42 bp alternating A-T) are consecutive elements in Zc2. Competition experiments strongly suggest that the three elements bind to the same protein. Protein-DNA interaction was detected in endosperm nuclear extracts of 8 to 21 days after pollination (DAP), as well as in 25 DAP embryos and in different tissues from plantlets. The protein factor has an MWapp of ca. 30 kDa. This factor has properties suggesting it is an HMG-like protein. These results are consistent with a growing accumulation of data for a number of genes indicating that A/T-rich elements, located at distal and proximal zones of the 5'-flanking sequences, interact with HMG-like proteins.

Base Composition↗
PubMed1992

Percutaneous absorption and skin distribution of [14C]flutrimazole in mini-pigs.

The percutaneous absorption and skin distribution of a skin cream containing 1% 14C-labelled 1-[(fluorophenyl) (4-fluorophenyl) phenylmethyl]-1H-imidazole (flutrimazole, UR-4056, CAS 119006-77-8) was studied in minipigs. The same dose of flutrimazole was administered i.v. and topically (as a cream) on scarified skin according to a crossover protocol. Samples of urine and faeces were taken at various intervals after administration, and radioactivity was measured. The percentage of radioactivity accumulated in urine after topical and intravenous administration were 1.46% and 41.7%, respectively. In faeces, the percentage of radioactivity observed was 6.0% after intravenous administration, and none was detected after topical application. In order to study the distribution and penetration of [14C]flutrimazole, the cream was applied to intact and scarified skin. At various intervals after administration, skin samples were taken. The samples for the autoradiographic studies were cut transversely, and for the measurement of the levels of radioactivity at different skin depths, slices were cut parallel to the cutaneous layers. The results obtained indicate that [14C]flutrimazole penetrates quickly into the different epidermic layers and is retained mainly in the strata spinosum, granulosum and basale. The stratum basale possibly acts as a selective barrier preventing the penetration of the compound into the dermis. The percentage of radioactivity in the stratum corneum is lower than that detected in all the other epidermic layers taken together. The stratum corneum offers low resistance to penetration by the flutrimazole, which very probably crosses the epidermic strata by a transcellular route.

Animals↗
PubMed1992

Molecular basis of familial chylomicronemia: mutations in the lipoprotein lipase and apolipoprotein C-II genes.

The molecular basis of familial chylomicronemia (type I hyperlipoproteinemia), a rare autosomal recessive trait, was investigated in six unrelated individuals (five of Spanish descent and one of Northern European extraction). DNA amplification by polymerase chain reaction (PCR) followed by single strand conformation polymorphism (SSCP) analysis allowed rapid identification of the underlying mutations. Six different mutant alleles (three of which are previously undescribed) of the gene encoding lipoprotein lipase (LPL) were discovered in the five LPL-deficient patients. These included an 11 bp deletion in exon 2, and five missense mutations: Trp 86 Arg (exon 3), His 136 Arg (exon 4), Gly 188 Glu (exon 5), Ile 194 Thr (exon 5), and Ile 205 Ser (exon 5). The Trp 86 Arg mutation is the only known missense mutation in exon 3. The other missense mutations lie in the highly conserved "central homology region" in close proximity with the catalytic site of LPL. These and other previously reported missense mutations provide insight into structure/function relationships in the lipase family. The missense mutations point to the important role of particular highly conserved helices and beta-strands in proper folding of the LPL molecule, and of certain connecting loops in the catalytic process. A nonsense mutation (Arg 19 Term) in the gene encoding apolipoprotein C-II (apoC-II), the cofactor of LPL, was found to underlie chylomicronemia in the sixth patient who had normal LPL but was apoC-II-deficient.

Adolescent↗
PubMed1991

Lipoprotein lipase in lungs, spleen, and liver: synthesis and distribution.

Lipoprotein lipase (LPL, E C 3.1.1.34) is the enzyme responsible for hydrolysis of triacylglycerols in plasma lipoproteins, making the fatty acids available for use by subjacent tissues. LPL is functional at the surface of endothelial cells, but it is not clear which cells synthesize the enzyme and what its distribution within tissues and vessels is. In previous studies we reported that in the major LPL-producing tissues (muscles, adipose tissue, and mammary gland) the enzyme is made by the major cell types. In the present work we have studied in adult guinea pigs some tissues that present LPL activity but in lower amounts (lung, spleen, and liver). On cryosections of these tissues we have searched for specific cell expression of the LPL gene (by in situ hybridization using a RNA probe) and for the corresponding protein distribution (by immunocytochemistry). Based on morphological criteria we can suggest that, contrary to the main LPL-producing tissues, in these tissues the enzyme is made by scattered cells, such as macrophages in the lung and spleen and Kupffer cells in the liver; endothelial cells present but do not synthesize the enzyme, indicating that the endothelial LPL originates in other cells. In the liver strong immunoreaction was detected in the sinusoid in contrast to the low level of mRNA expression, suggesting that liver takes up circulating LPL from blood.

Animals↗