Characterization of the apolipoprotein(a) gene

Immune Tolerance in Mytilus galloprovincialis Hemocytes After Repeated Contact With Vibrio splendidus

Mediterranean mussels (Mytilus galloprovincialis) are sessile filter feeders that live in close contact with numerous marine microorganisms. As is the case in all invertebrates, mussels lack an adaptive immune system, but they respond to pathogens, injuries or environmental stress in a very efficient manner. However, it is not known if they are able to modify their immune response when they reencounter the same pathogen. In this work, we studied the transcriptomic response of mussel hemocytes before and after two consecutive sublethal challenges with Vibrio splendidus. The first exposure significantly regulated genes related to inflammation, migration and response to bacteria. However, after the second exposure, the differentially expressed genes were related to the control and inhibition of ROS production and the resolution of the inflammatory response. Our results also show that the second injection with V. splendidus led to changes at the transcriptional (control of the expression of pro-inflammatory transcripts), cellular (shift in the hemocyte population distribution), and functional levels (inhibition of ROS production). These results suggest that a modified immune response after the second challenge allowed the mussels to tolerate rather than fight the infection, which minimized tissue damage.

Structure, function, and genetics of lipoprotein (a)

Lipoprotein (a) [Lp(a)] has attracted the interest of researchers and physicians due to its intriguing properties, including an intragenic multiallelic copy number variation in the LPA gene and the strong association with coronary heart disease (CHD). This review summarizes present knowledge of the structure, function, and genetics of Lp(a) with emphasis on the molecular and population genetics of the Lp(a)/LPA trait, as well as aspects of genetic epidemiology. It highlights the role of genetics in establishing Lp(a) as a risk factor for CHD, but also discusses uncertainties, controversies, and lack of knowledge on several aspects of the genetic Lp(a) trait, not least its function.

Lipoprotein(a), atherosclerosis, and apolipoprotein(a) gene polymorphism

High plasma lipoprotein(a) [Lp(a)] levels have been implicated as an independent risk factor for coronary artery disease in Caucasians, Chinese, Africans, and Indians. Apo(a) that evolved from a duplicated plasminogen gene during recent primate evolution is responsible for the concentration of Lp(a) in the artery wall leading to atherosclerosis, by virtue of its ability to bind to the extracellular matrix and its role in stimulating the proliferation and migration of human smooth muscle cells. Several types of polymorphisms, size as well as sequence changes both in the coding and regulatory sequences, have been reported to influence the variability of Lp(a) concentration. Apo(a) exhibits genetic size polymorphism varying between 300 and 800 kDa that could be attributed to the number of k-4 VNTR (variable number of transcribed kringle-4 repeats). An inverse relationship between Lp(a) level and apo(a) allele sizes is a general trend in all ethnic populations although apo(a) allele size distribution could be significantly variable in ethnic types. A negative correlation between the number of pentanucleotide TTTTA(n) repeat (PNR) sequences in the regulatory region of the apo(a) gene and Lp(a) level has also been observed in Caucasians and Indians, but not in African Americans. However, a significant linkage disequilibrium was noted between the PNR number and k-4 VNTR. In order to correlate the role of apo(a) gene polymorphisms to apo(a) gene regulation, we have proposed that liver-specific transcriptional activators and repressors might contribute to the differential expression of apo(a) gene, in an individual-specific manner.

Expression of plasminogen-related gene B varies among normal tissues and increases in cancer tissues

We previously found that the promoter activity of plasminogen (PLG)-related gene B (PRGB) was 5-fold that of PLG. We have since examined the transcript levels of PRGB among various normal human tissues, and compared these findings with those of PLG. Reverse transcription-PCR analysis revealed that the PRGB expression varied widely among different tissues, while PLG was expressed only in the liver and kidney. RNA samples obtained from cultured cell lines also demonstrated differing PRGB expression. Furthermore, increased PRGB expression was observed in several fresh samples of cancer tissue obtained from cancer patients when compared with surrounding normal tissues.

Multi-modal expression of apolipoprotein (a) gene in vivo

The apolipoprotein (a) [apo(a)] gene encodes a protein component of lipoprotein (a) [Lp(a)] whose plasma levels vary among individuals. To study the implications of Lp(a), we examined plasma Lp(a) levels and molecular weights of apo(a) in patients with cerebrovascular disease (CVD) or diabetes mellitus (DN). Mean Lp(a) concentrations were higher in the CVD cases with atherothrombotic brain infarction than in those with brain hemorrhage and lacunar infarction. Lp(a) levels were lower in the DM cases on diet therapy alone than in those treated with insulin or oral hypoglycemic agents. These results suggest that Lp(a) is thrombogenic and atherogenic, and that insulin may modulate Lp(a) levels. We subclassified the apo(a) gene into four types (A-D) by polymorphisms in the 5'-flanking region. We also measured plasma Lp(a) concentrations and examined expression of the gene by an in vitro assay. Homozygotes of type C had higher Lp(a) levels than those of type D, and the relative expression of type C was higher than that of type D in vitro. Lp(a) levels, however, varied even within the same 5'-allele having similar apo(a) isoforms. Thus, Lp(a) concentrations are genetically determined and may be modified by some hormones and cytokines. When we examined transcript levels for apo(a) by RT-PCR in various normal tissues, apo(a) was strongly expressed in liver while not in thyroid or leukocytes. Small amounts of apo(a) transcript were observed in all other organs and tissues. Apo(a) in these tissues may also play a role in inframmation, tissue remodeling, cell migration, and other physiological functions.

Plasma lipoprotein(a) levels are high in patients with central retinal artery occlusion

High plasma lipoprotein(a) (Lp[a]) concentration is an independent risk factor for atherosclerosis and thrombosis. To study the implications of Lp(a) in central retinal artery occlusion (CRAO), we examined Lp(a) levels and molecular weights (MWs) of apolipoprotein(a) (apo(a)). Mean Lp(a) concentration was significantly higher in the cases with CRAO than in the controls. Lp(a) levels higher than 30 mg/dl were also more frequent in the CRAO cases than in the controls. Lp(a) concentrations correlated significantly with low-MW isoforms of apo(a). Impaired fibrinolysis and atherogenesis induced by Lp(a) may play a role in the pathophysiology of CRAO. Since high Lp(a) levels were reported in CRVO by other investigators, patients with central retinal vein occlusion (CRVO) were also examined for Lp(a). Although Lp(a) levels were higher in the CRVO cases than in the controls, the difference was not significant. Therefore, high Lp(a) levels may not be associated with venous thrombosis and/or embolism.

Lipoprotein(a) concentration and molecular weight of apolipoprotein(a) in patients with cerebrovascular disease and diabetes mellitus

Plasma lipoprotein(a) [Lp(a)] concentrations are genetically determined, and hyper-Lp(a)-emia is an independent risk factor for atherosclerosis and thrombosis. To study the implications of Lp(a) in cerebrovascular disease (CVD) and diabetes mellitus (DM), we examined plasma Lp(a) levels and molecular weights of apolipoprotein(a) [apo(a)] in 118 patients with CVD, and 125 cases with DM. Although mean Lp(a) concentrations were higher in those cases with atherothrombotic brain infarction than in those with brain hemorrhage and lacunar infarction, the difference was not statistically significant. Lp(a) levels were significantly higher in the DM cases treated with insulin and in those treated with oral hypoglycemic agents than in those on diet therapy alone, suggesting that insulin and oral agents modulate apo(a) expression. Lp(a) concentrations correlated significantly with the low-molecular-weight isoforms of apo(a) in all CVD and DM groups.

Plasma lipoprotein(a) levels and expression of the apolipoprotein(a) gene are dependent on the nucleotide polymorphisms in its 5'-flanking region

The apolipoprotein(a) (apo[a]) gene encodes a protein component of lipoprotein(a) [Lp(a)] whose plasma levels vary widely among individuals. Hyper-Lp(a)-emia constitutes a risk factor for thromboembolic disease. We previously subclassified the apo(a) gene into four allelic types (A-D) by polymorphisms in the 5'-flanking region. To elucidate whether these polymorphisms affect the expression of apo(a), we measured plasma Lp(a) concentrations in vivo by ELISA and examined expression of the gene by an in vitro assay using its 5'-flanking region. Homozygotes of type C had significantly higher Lp(a) levels than those of type D. The relative expression of type C was also about three times higher than that of type D, which was consistent with the in vivo results. Deletion analysis revealed that the substitution of C by T (+93) led to negative regulation in expression of the gene, while the change of G to A (+121) led to positive regulation. These results indicate that the polymorphisms in the 5'-flanking region of the apo(a) gene affect the efficiency of its expression and, in part, play a role in regulating plasma Lp(a) levels.

Expression and induction by IL-6 of the normal and variant genes for human plasminogen

We examined the promoter activity of the gene for human plasminogen (PLG) employing its 1.1 kb fragment of the 5'-flanking region inserted in front of a reporter gene. Deletion analysis revealed that a region surrounding the transcription start site was essential for the PLG expression. Since the PLG gene has three sequences for the interleukin-6 (IL-6) responsive element, we examined the effect of IL-6 on the PLG expression. IL-6 stimulation of PLG resulted in a 2.5-fold increase in its transcription. This is also true for the PLG gene of a case with dysplasminogenemia. Although the patient's gene had six mutations in the 5'-flanking region, its promoter activity was 1.8-fold that of normal PLG.