MicroRNAs regulating lipid metabolism in atherogenesis

miRNA expression profiles determined in maternal sera of patients with HELLP syndrome

OBJECTIVE

Syndrome of hemolysis, elevated liver enzymes and low platelets (HELLP) represents a distinct subgroup of severe preeclampsia. The aim of our study was to identify differentially expressed miRNAs in sera of patients with HELLP syndrome in comparison to unaffected controls.

STUDY DESIGN

Blood samples were obtained from patients with manifest HELLP syndrome and matched unaffected controls. The expression of 754 mature miRNAs was assessed using the TaqMan Array format (n = 12). Results of seven differentially expressed miRNAs were further validated by single quantitative real-time polymerase chain reaction (qPCR) assays.

RESULTS

Serum miRNA analysis allowed detection of maternal and fetal miRNAs. Distinct miRNA expressions were confirmed for miR-122, miR-758 and miR-133a represented by a median up-regulation ≥ two-fold in the HELLP group. The liver specific miR-122 was 11.5-fold increased with an area under curve (AUC) of 0.82 in the receiver operating characteristic (ROC) analysis. Cluster analyses of our data uncovered subgroups of HELLP patients were associated with clinical subtypes and differences in organ manifestation.

CONCLUSION

In our proof of principle study, we demonstrated that patients with HELLP syndrome showed alterations of serum miRNA expression patterns. Data analysis goes along with the hypothesis that HELLP syndrome is regarded to be a heterogeneous disease.

MicroRNA associated with dyslipidemia and coronary disease in humans

MicroRNAs are structural components of an epigenetic mechanism of posttranscriptional regulation of messenger RNA translation. Recently, there has been significant interest in the application of microRNA as a blood-based biomarker of underlying physiological conditions. Dyslipidemia is a complex, heterogeneous condition conferring substantially increased risk for cardiovascular disease. The purpose of this review is to describe the current body of knowledge on the role of microRNA regulation of lipoprotein metabolism in humans and to discuss relevant methodological and study design considerations. We highlight the potential roles for microRNA in gene-environment interactions.

Differential miRNA expression profiles between the first and third trimester human placentas

To determine placental microRNA (miRNA) expression at different gestational age, total RNA from six first and six third trimester placentas was isolated. miRNA expression was analyzed by Affymetrix miRNA microarray, and miRNA clusters were identified by web-based programs MirClust and miRGen Cluster. qRT-PCR was carried out to validate miRNA expression, and in situ hybridization (ISH) was performed to determine compartmental localization of miRNAs within villous tissue. A total of 208 miRNA transcripts, which represent 191 mature miRNAs, were found differently expressed between first and third trimester placentas. miRNAs within the miR-17-92 cluster, C14MC, miR-371 cluster, and C19MC were significantly upregulated in the first trimester placentas. In contrast, miRNAs of the let-7 family, miR-34 family, miR-29a cluster, miR-195 cluster, and miR-181c cluster were significantly upregulated in the third trimester placentas. Increased miR-371-5p, miR-17-3p, and miR-708-5p expression and decreased miR-125b-5p and miR-139-5p expression in the first trimester placentas were confirmed by qRT-PCR. Different expression pattern for miR-371-5p and miR-125b-5p within villous tissue was demonstrated by ISH. Distinct miRNA cluster expression profiles between the first and third trimester placentas were identified. miRNAs that regulate innate/adaptive immune responses are strongly expressed in both first and third trimester placentas. miRNAs that exert oncogenic, angiogenic, and antiapoptotic properties are dominantly expressed in the first trimester placentas, whereas miRNAs that promote cell differentiation and function as tumor suppressors are strongly expressed in the third trimester placentas. These results indicate that miRNAs play critical roles in placental development.

Needles in the genetic haystack of lipid disorders: single nucleotide polymorphisms in the microRNA regulome

In recent years, microRNAs (miRNA) have emerged as important posttranscriptional regulators of gene expression in a wide variety of biological pathways. Since the discovery of the liver-specific miRNA-122 (miR-122) and its critical role in hepatic function, numerous additional miRNAs have been implicated in lipid metabolism. It is now apparent that lipid homeostasis is governed in part by an intricate web of miRNA activity. miRNAs are thought to confer robustness against environmental changes, such as diet modifications. Therefore, naturally occurring genetic variation that perturbs miRNA expression and/or function is likely to contribute to interindividual variability in lipid phenotypes. Although the field is still in its infancy, this review describes the growing evidence for miRNA-related genetic variation as etiological factors in lipid disorders. Specific examples, including a variant in a miRNA transcriptional control element that leads to dyslipidemia as well as a variant in a miRNA target site that modulates the effect of diet on plasma lipid levels, are discussed. Finally, the utility of recent systems genetics approaches to uncover hidden miRNA-related genetic associations with lipid disorders are considered, thereby illuminating the needles in the genetic haystack.

Complexity of microRNA function and the role of isomiRs in lipid homeostasis

MicroRNAs (miRNAs) are key posttranscriptional regulators of biological pathways that govern lipid metabolic phenotypes. Recent advances in high-throughput small RNA sequencing technology have revealed the complex and dynamic repertoire of miRNAs. Specifically, it has been demonstrated that a single genomic locus can give rise to multiple, functionally distinct miRNA isoforms (isomiR). There are several mechanisms by which isomiRs can be generated, including processing heterogeneity and posttranscriptional modifications, such as RNA editing, exonuclease-mediated nucleotide trimming, and/or nontemplated nucleotide addition (NTA). NTAs are dominant at the 3'-end of a miRNA, are most commonly uridylation or adenlyation events, and are catalyzed by one or more of several nucleotidyl transferase enzymes. 3' NTAs can affect miRNA stability and/or activity and are physiologically regulated, whereas modifications to the 5'-ends of miRNAs likely alter miRNA targeting activity. Recent evidence also suggests that the biogenesis of specific miRNAs, or small RNAs that act as miRNAs, can occur through unconventional mechanisms that circumvent key canonical miRNA processing steps. The unveiling of miRNA diversity has significantly added to our view of the complexity of miRNA function. In this review we present the current understanding of the biological relevance of isomiRs and their potential role in regulating lipid metabolism.

MicroRNAs and lipoproteins: a connection beyond atherosclerosis?

MicroRNAs (miRNAs) are short non-coding RNAs involved in the regulation of gene expression at the post-transcriptional level that have been involved in the pathogenesis of a number of cardiovascular diseases. Several miRNAs have been described to finely regulate lipid metabolism and the progression and regression of atherosclerosis including, miR-33, miR-122. Of note miR-33a and -33b, represent one of the most interesting and attractive targets for metabolic-related disorders and anti-miR-33 approaches are under intensive investigation. More recently miRNAs were shown to exert their activities in a paracrine manner and also systemically. The latter is possible because lipid-carriers, including lipoproteins, transport and protect miRNAs from degradation in the circulation. This review will present the complex mechanism by which miRNAs regulate lipid metabolism, illustrate how their therapeutical modulation may lead to new treatments for cardiometabolic diseases, and discuss how lipoproteins and other lipid-carriers transport miRNAs in the circulation. The emerging strong connection between miRNAs, lipoproteins and lipid metabolism indicates the existence of a reciprocal modulation that might go beyond atherosclerosis.