Enhanced protein production by microRNA-30 family in CHO cells is mediated by the modulation of the ubiquitin pathway

Stable overexpression of native and artificial miRNAs for the production of differentially fucosylated antibodies in CHO cells

Cell engineering strategies typically rely on energy-consuming overexpression of genes or radical gene-knock out. Both strategies are not particularly convenient for the generation of slightly modulated phenotypes, as needed in biosimilar development of for example differentially fucosylated monoclonal antibodies (mAbs). Recently, transiently transfected small noncoding microRNAs (miRNAs), known to be regulators of entire gene networks, have emerged as potent fucosylation modulators in Chinese hamster ovary (CHO) production cells. Here, we demonstrate the applicability of stable miRNA overexpression in CHO production cells to adjust the fucosylation pattern of mAbs as a model phenotype. For this purpose, we applied a miRNA chaining strategy to achieve adjustability of fucosylation in stable cell pools. In addition, we were able to implement recently developed artificial miRNAs (amiRNAs) based on native miRNA sequences into a stable CHO expression system to even further fine-tune fucosylation regulation. Our results demonstrate the potential of miRNAs as a versatile tool to control mAb fucosylation in CHO production cells without adverse side effects on important process parameters.

Multi-lipase gene knockdown in Chinese hamster ovary cells using artificial microRNAs to reduce host cell protein mediated polysorbate degradation

A large number of companies observe polysorbate (PS) degradation and associated (sub-)visible particle formation in biological drug formulations, which compromise the stability of the drug product, ultimately posing a risk toward delivering innovative medicines to patients. The main culprits of PS degradation are hydrolytic host cell proteins (HCPs) originating from the production cell lines, which are mostly Chinese hamster ovary (CHO) cell derived. Here, a small portion of particularly difficult-to-remove HCPs-mainly lipases-cause hydrolytic cleavage of PS resulting in the accumulation of free fatty acid aggregates/particles. One possible mitigation strategy is the removal of such critical HCPs in the production cell line. Multigene regulation can be achieved via microRNAs (miRNAs) thereby serving as a smart tool to reduce the expression of different target genes using a single miRNA. To enable a tailored gene regulation of multiple specific target lipases self-designed and non-naturally occurring artificial miRNAs (amiRNA) can be designed. Based on micro-conserved regions in the mRNA sequence of two sets of target HCPs, we provide a proof-of-concept for a simultaneous multi-lipase knockdown in CHO cells using single amiRNAs. By this, we were not only able to reduce PS degradation but laid the foundation to expand this tool to other areas of cell line phenotype engineering.

Overexpression of miR-32 in Chinese hamster ovary cells increases production of Fc-fusion protein

The demand for industrial genetically modified host cells were increased with the growth of the biopharmaceutical market. Numerous studies on improving host cell productivity have shown that altering host cell growth and viability through genetic engineering can increase recombinant protein production. During the last decades, it was demonstrated that overexpression or downregulation of some microRNAs in Chinese Hamster Ovary (CHO) cells as the host cell in biopharmaceutical manufacturing, can improve their productivity. The selection of microRNA targets has been based on their previously identified role in human cancers. MicroRNA-32 (miR-32), which is conserved between humans and hamsters (Crisetulus griseus), was shown to play a role in the regulation of cell proliferation and apoptosis in some human cancers. In this study, we investigated the effect of miR-32 overexpression on the productivity of CHO-VEGF-trap cells. Our results indicated that stable overexpression of miR-32 could dramatically increase the productivity of CHO cells by 1.8-fold. It also significantly increases cell viability, batch culture longevity, and cell growth. To achieve these results, following the construction of a single clone producing an Fc-fusion protein, we transfected cells with a pLexJRed-miR-32 plasmid to stably produce the microRNA and evaluate the impact of mir-32 overexpression on cell productivity, growth and viability in compare with scrambled control. Our findings highlight the application of miRNAs as engineering tools and indicated that miR-32 could be a target for engineering CHO cells to increase cell productivity.

MicroRNA Expression Variation in Female Dog (Canis familiaris) Reproductive Organs with Age and Presence of Uteropathy

While aging is associated with microRNA (miRNA) expression, little is known about its role in the aging of dog reproductive organs. We examined miRNA expression in ovaries, oviducts, and uteri from young and old dogs and dogs with uteropathy to elucidate miRNA's role in aging. The ovaries, oviducts, and uteri of 18 dogs (Canis familiaris)-young (8.5 ± 1.9 months old), old (78.2 ± 29.0 months old), and those with uteropathy (104.4 ± 15.1 months old)-were collected for miRNA expression examination. Total RNA samples were extracted, reverse-transcribed to cDNA, and real-time PCR analysis was also performed. In ovaries, miR-708 and miR-151 levels were significantly higher in old dogs than in young dogs, and only let-7a, let-7b, let-7c, miR125b, and miR26a were significantly upregulated in dogs with uteropathy. In the oviducts and uteri of old dogs, miR-140, miR-30d, miR-23a, miR-10a, miR-125a, miR-221, and miR-29a were upregulated. Realtime quantitative PCR revealed that targeted mRNA was similarly regulated to miRNA. These results suggest that miRNAs of reproductive organs in dogs may be biological markers for aging and reproductive diseases and could be used for mediating aging.

Recent developments in miRNA based recombinant protein expression in CHO

It is widely accepted that the growing demand for recombinant therapeutic proteins has led to the expansion of the biopharmaceutical industry and the development of strategies to increase recombinant protein production in mammalian cell lines such as SP2/0 HEK and particularly Chinese hamster ovary cells. For a long time now, most investigations have been focused on increasing host cell productivity using genetic manipulating of cellular processes like cell cycle, apoptosis, cell growth, protein secretory and other pathways. In recent decades MicroRNAs beside different genetic engineering tools (e.g., TALEN, ZFN, and Crisper/Cas) have attracted further attention as a tool in the genetic engineering of host cells to increase protein expression levels. Their ability to simultaneously target multiple mRNAs involved in one or more cellular processes made them a favorable tool in this field. Accordingly, this study aimed to review the methods of selecting target miRNA for cell line engineering, miRNA gain- or loss-of-function strategies, examples of laboratory and pilot studies in this field and discussed advantages and disadvantages of this technology.

The Effect of microRNA on the Production of Recombinant Protein in CHO Cells and its Mechanism

Recombinant protein production by mammalian cells is the initial step in the manufacture of many therapeutic proteins. Chinese hamster ovary (CHO) cells are the most common host system to produce recombinant therapeutic proteins (RTPs). However, it is still challenging to maintain high productivity ensuring the good quality of RTPs produced by CHO cells. MicroRNAs(miRNAs) are short regulatory non-coding RNAs that can regulate cellular behavior and complex phenotypes. It has been found that miRNAs can enhance the expression level of recombinant proteins in CHO cells by promoting proliferation, resisting apoptosis, and regulating metabolism. miRNAs also can affect the quality of RTPs. In this review, we will discuss the effect and mechanism of miRNA on the expression level and quality of recombinant proteins in CHO cells.

A blueprint from nature: miRNome comparison of plasma cells and CHO cells to optimize therapeutic antibody production

Chinese Hamster Ovary (CHO) cells are the most frequently used biopharmaceutical production hosts, although industry is presently suffering from their variable recombinant product quality, insufficient long-term stability and low productivity. Here, we present an effort to address overall cell line engineering by a novel bottom-up microRNA (miRNA) screening approach. miRNAs are small non-coding RNAs known to regulate global gene expression at the post-transcriptional level and have proved to serve as promising tools for cell line engineering for over a decade. Here the miRNome of plasma cells (PCs) has been analyzed as the natural blueprint for optimized production and secretion of antibodies. Performing comparative miRNome cross-species expression analysis of four murine/human PC-derived (PCD) and two CHO cell lines showed 147 conserved miRNAs to be differentially expressed between PCDs and CHOs. Conducting a targeted miRNA screen of this PC-specific miRNA subset revealed 14 miRNAs to improve bioprocess relevant parameters in CHO cells, among them the PC-characteristic miR-183 cluster. Finally, miRNA target prediction tools and transcriptome analysis were combined to elucidate differentially regulated lysine degradation and fatty acid metabolism pathways in monoclonal antibody (mAb) expressing CHO-DG44 and CHO-K1 cells, respectively. Thus, substantial new insights into molecular and cellular mechanisms of biopharmaceutical production cell lines can be gained by targeted bottom-up miRNA screenings.

The emerging role of cellular post-translational modifications in modulating growth and productivity of recombinant Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells are one of the most commonly used host cell lines used for the production human therapeutic proteins. Much research over the past two decades has focussed on improving the growth, titre and cell specific productivity of CHO cells and in turn lowering the costs associated with production of recombinant proteins. CHO cell engineering has become of particular interest in recent years following the publication of the CHO cell genome and the availability of data relating to the proteome, transcriptome and metabolome of CHO cells. However, data relating to the cellular post-translational modification (PTMs) which can affect the functionality of CHO cellular proteins has only begun to be presented in recent years. PTMs are important to many cellular processes and can further alter proteins by increasing the complexity of proteins and their interactions. In this review, we describe the research presented from CHO cells to date related on three of the most important PTMs; glycosylation, phosphorylation and ubiquitination.

MicroRNAs overexpressed in Crohn's disease and their interactions with mechanisms of epigenetic regulation explain novel aspects of Crohn's disease pathogenesis

Background

In this review, we were interested to identify the wide universe of enzymes associated with epigenetic modifications, whose gene expression is regulated by miRNAs with a high relative abundance in Crohn's disease (CD) affected tissues, with the aim to determine their impact in the pathogenesis and evolution of the disease.

Methods

We used HMDD and Bibliometrix R-package in order to identify the miRNAs overexpressed in CD. The identified enzymes associated with epigenetic mechanisms and post-translational modifications, regulated by miRNAs upregulated in CD, were analyzed using String v11 database.

Results

We found 190 miRNAs with great abundance in patients with CD, of which 26 miRNAs regulate the gene expression of enzymes known to catalyze epigenetic modifications involved in essentials pathophysiological processes, such as chromatin architecture reorganization, immune response regulation including CD4+ T cells polarization, integrity of gut mucosa, gut microbiota composition and tumorigenesis.

Conclusion

The integrated analysis of miRNAs with a high relative abundance in patients with CD showed a combined and superimposed gene expression regulation of enzymes associated with relevant epigenetic mechanisms and that could explain, in part, the pathogenesis of CD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-021-01022-8.

Transferability of miRNA-technology to bioprocessing: Influence of cultivation mode and media

The biopharmaceutical industry strives for improvement of their production processes. In recent years, miRNAs have been shown to positively impact the production capacity of recombinant CHO cells, especially with regard to difficult to express proteins. Effective and reliable gene regulation of process relevant target genes by miRNAs is a prerequisite for integrating them into the toolbox of industrial cell engineering strategies. However, most studies rely on transient transfection of miRNA mimics; there is low standardization in evaluation of miRNA function and little knowledge on transferability of effects found during transient expression to stable expression during industry relevant fed‐batch cultivation. In order to provide more insight into this topic, we used the pcDNA6.2 vector for stable miRNA overexpression during batch and fed‐batch cultivation in CHO DG44 cells, optimized the vector, and compared the miRNA levels and effects with those achieved by transfection of miRNA mimics. We found that miR‐1 downregulated TWF1 mRNA in different recombinant CHO DG44 clones in a dose‐dependent manner during transient batch cultivation. Cells stably overexpressing miR‐1 also showed a TWF1 mRNA downregulation when cultivated in batch mode using in‐house medium 1. However, when the cells stably overexpressing miR‐1 were cultivated in fed‐batch mode using in‐house medium 2. Consequently, a change of cultivation mode and medium seems to have an impact on target gene regulation by miRNA. Taken together, our findings highlight the importance to standardize miRNA evaluations and test miRNAs in the final application environment.

CRISPR/Cas9-Mediated Knockout of MicroRNA-744 Improves Antibody Titer of CHO Production Cell Lines

MicroRNAs (miRNAs) are noncoding RNAs that serve as versatile molecular engineering tools to improve production cells by overexpression or knockdown of miRNAs showing beneficial or adverse effects on cell-culture performance. The genomic knockout (KO) of noncoding RNAs in Chinese hamster ovary (CHO) production cells has not been reported. However, given the significant number of miRNAs showing negative effects on CHO-bioprocess performance and the development of clustered regularly interspaced short palindromic repeats/CRISPR-associated proteins (CRISPR/Cas9), genome editing tools facilitate precise optimization of CHO cells via modulation of noncoding RNAs. In a previous high-content miRNA screen, miR-744 was identified as a potential target associated with reduced productivity. Hence, the genomic miR-744 precursor sequence is deleted by two single guide RNA (sgRNA)-Cas9-mediated DNA double-strand breaks (DSB) flanking the miR-744 locus. After fluorescence-activated cell sorting (FACS), clonal miR-744 KO cell lines are recovered and three of them are confirmed as miR-744 KOs. Impacts of CRISPR/Cas9 editing are characterized at the genetic, transcript, and phenotypic levels. During batch cultivation, antibody titers of miR-744 KOs are significantly increased to 190-311 mg L-1 compared to a nontargeting (NT) sgRNA transfected clonal control with 156 mg L-1 , pointing towards the potential of miRNA KO for cell line engineering.

miR-30 Family: A Promising Regulator in Development and Disease

MicroRNAs (miRNAs) are small noncoding RNAs that negatively regulate posttranscriptional expression of target genes. Accumulating evidences have demonstrated that the miR-30 family, as a member of microRNAs, played a crucial regulating role in the development of tissues and organs and the pathogenesis of clinical diseases, which indicated that it may be a promising regulator in development and disease. This review aims to clarify the current progress on the regulating role of miR-30 family in tissues and organs development and related disease and highlight their research prospective in the future.

Stable miRNA overexpression in human CAP cells: Engineering alternative production systems for advanced manufacturing of biologics using miR-136 and miR-3074

Chinese hamster ovary (CHO) cells still represent the major production host for therapeutic proteins. However, multiple limitations have been acknowledged leading to the search for alternative expression systems. CEVEC's amniocyte production (CAP) cells are human production cells demonstrated to enable efficient overexpression of recombinant proteins with human glycosylation pattern. However, CAP cells have not yet undergone any engineering approaches to optimize process parameters for a cheaper and more sustainable production of biopharmaceuticals. Thus, we assessed the possibility to enhance CAP cell production capacity via cell engineering using miRNA technology. Based on a previous high-content miRNA screen in CHO-SEAP cells, selected pro-productive miRNAs including, miR-99b-3p, 30a-5p, 329-3p, 483-3p, 370-3p, 219-1-3p, 3074-5p, 136-3p, 30e-5p, 1a-3p, and 484-5p, were shown to act pro-productive and product independent upon transient transfection in CAP and CHO antibody expressing cell lines. Stable expression of miRNAs established seven CAP cell pools with an overexpression of the pro-productive miRNA strand. Subsequent small-scale screening as well as upscaling batch experiments identified miR-136 and miR-3074 to significantly increase final mAb concentration in CAP-mAb cells. Transcriptomic changes analyzed by microarrays identified several lncRNAs as well as growth and apoptosis-related miRNAs to be differentially regulated in CAP-mAb-miR-136 and -miR-3074. This study presents the first engineering approach to optimize the alternative human expression system of CAP-cells.

Methods for Using Small Non-Coding RNAs to Improve Recombinant Protein Expression in Mammalian Cells

The ability to produce recombinant proteins by utilizing different “cell factories” revolutionized the biotherapeutic and pharmaceutical industry. Chinese hamster ovary (CHO) cells are the dominant industrial producer, especially for antibodies. Human embryonic kidney cells (HEK), while not being as widely used as CHO cells, are used where CHO cells are unable to meet the needs for expression, such as growth factors. Therefore, improving recombinant protein expression from mammalian cells is a priority, and continuing effort is being devoted to this topic. Non-coding RNAs are RNA segments that are not translated into a protein and often have a regulatory role. Since their discovery, major progress has been made towards understanding their functions. Non-coding RNA has been investigated extensively in relation to disease, especially cancer, and recently they have also been used as a method for engineering cells to improve their protein expression capability. In this review, we provide information about methods used to identify non-coding RNAs with the potential of improving recombinant protein expression in mammalian cell lines.

Identifying HIPK1 as Target of miR-22-3p Enhancing Recombinant Protein Production From HEK 293 Cell by Using Microarray and HTP siRNA Screen

Protein expression from human embryonic kidney cells (HEK 293) is an important tool for structural and clinical studies. It is previously shown that microRNAs (small, noncoding RNAs) are effective means for improved protein expression from these cells, and by conducting a high-throughput screening of the human microRNA library, several microRNAs are identified as potential candidates for improving expression. From these, miR-22-3p is chosen for further study since it increased the expression of luciferase, two membrane proteins and a secreted fusion protein with minimal effect on the cells' growth and viability. Since each microRNA can interact with several gene targets, it is of interest to identify the repressed genes for understanding and exploring the improved expression mechanism for further implementation. Here, the authors describe a novel approach for identification of the target genes by integrating the differential gene expression analysis with information obtained from our previously conducted high-throughput siRNA screening. The identified genes were validated as being involved in improving luciferase expression by using siRNA and qRT-PCR. Repressing the target gene, HIPK1, is found to increase luciferase and GPC3 expression 3.3- and 2.2-fold, respectively.

miRNA engineering of CHO cells facilitates production of difficult-to-express proteins and increases success in cell line development

In recent years, coherent with growing biologics portfolios also the number of complex and thus difficult-to-express (DTE) therapeutic proteins has increased considerably. DTE proteins challenge bioprocess development and can include various therapeutic protein formats such as monoclonal antibodies (mAbs), multi-specific affinity scaffolds (e.g., bispecific antibodies), cytokines, or fusion proteins. Hence, the availability of robust and versatile Chinese hamster ovary (CHO) host cell factories is fundamental for high-yielding bioprocesses. MicroRNAs (miRNAs) have emerged as potent cell engineering tools to improve process performance of CHO manufacturing cell lines. However, there has not been any report demonstrating the impact of beneficial miRNAs on industrial cell line development (CLD) yet. To address this question, we established novel CHO host cells constitutively expressing a pro-productive miRNA: miR-557. Novel host cells were tested in two independent CLD campaigns using two different mAb candidates including a normal as well as a DTE antibody. Presence of miR-557 significantly enhanced each process step during CLD in a product independent manner. Stable expression of miR-557 increased the probability to identify high-producing cell clones. Furthermore, production cell lines derived from miR-557 expressing host cells exhibited significantly increased final product yields in fed-batch cultivation processes without compromising product quality. Strikingly, cells co-expressing miR-557 and a DTE antibody achieved a twofold increase in product titer compared to clones co-expressing a negative control miRNA. Thus, host cell engineering using miRNAs represents a promising tool to overcome limitations in industrial CLD especially with regard to DTE proteins. Biotechnol. Bioeng. 2017;114: 1495-1510. © 2017 Wiley Periodicals, Inc.

miR-92a enhances recombinant protein productivity in CHO cells by increasing intracellular cholesterol levels

MicroRNAs (miRNAs) have emerged as promising targets for engineering of CHO cell factories to enhance recombinant protein productivity. Manipulation of miRNA levels in CHO cells have been shown to improve product yield by increasing proliferation and specific productivity (qP), resisting apoptosis and enhancing oxidative metabolism. The authors previously demonstrated that over-expressing miR-92a results in increases in qP and titer of CHO-IgG cells. However, the mechanisms by which miR-92a enhances qP in CHO cells are still uninvestigated. Here, the authors report the identification of insig1, a regulator of cholesterol biosynthesis, as a target of miR-92a using computational prediction. Both transient and stable over-expression of miR-92a decreased the expression levels of insig1. Insig1 was further validated as a target of miR-92a using 3' UTR reporter assay. Intracellular cholesterol concentration of two high-producing miR-92a clones were significantly increased by ≈30% compared to the blank-transfected pool. Relative Golgi surface area was also found to be 18-26% higher in these clones. Our findings suggest that miR-92a may affect cholesterol metabolism by repressing insig1, resulting in raised intracellular cholesterol levels and Golgi volume and hence enhanced protein secretion.

MicroRNA-17-5p: At the Crossroads of Cancer and Aging - A Mini-Review

The miR-17-92 cluster, led by its most prominent member, miR-17-5p, has been identified as the first miRNA with oncogenic potential. Thus, the whole cluster containing miR-17-5p has been termed oncomiR-1. It is strongly expressed in embryonic stem cells and has essential roles in vital processes like cell cycle regulation, proliferation and apoptosis. The importance of miR-17-5p for fundamental biological processes is underscored by the fact that a miR17-deficient mouse is neonatally lethal. Recently, miR-17-5p was identified in the context of aging, since it is comprised in a common signature of miRNAs that is downregulated in several models of aging research. Recently, miR-17-5p turned out to be the first 'longevimiR' in an animal model, extending the lifespan of a transgenic miR-17-5p-overexpressing mouse. Here, we summarize the current status of research on miR-17-5p with emphasis on its role in cellular senescence, aging and cancer, which points to a pleiotropic function of miR-17-5p regulating multiple targets involved in autophagy, cell cycle regulation and apoptosis in a tissue-dependent fashion. In addition, its elevated presence in serum or plasma of a wide range of tumor patients suggests using it as an 'alarmiR', a general indicator of a potential tumor pathology. However, amounts of circulating miR-17-5p of healthy individuals as reference values are still missing, before any miRNA can be classified as such an 'alarmiR'. In conclusion, miR-17-5p is at the crossroads of aging, longevity and cancer and might represent a promising biomarker or even therapeutic tool and target in this context.

Hyperosmotic stimulus study discloses benefits in ATP supply and reveals miRNA/mRNA targets to improve recombinant protein production of CHO cells

Biopharmaceuticals are predominantly produced by Chinese hamster ovary (CHO) cells cultivated in fed-batch mode. Hyperosmotic culture conditions (≥ 350 mOsmol kg(∑1) ) resulting from feeding of nutrients may enhance specific product formation rates (qp ). As an improved ATP supply was anticipated to enhance qp this study focused on the identification of suitable miRNA/mRNA targets to increase ATP levels. Therefor next generation sequencing and a compartment specific metabolomics approach were applied to analyze the response of an antibody (mAB) producing CHO cell line upon osmotic shift (280 → 430 mOsmol kg(-1) ). Hyperosmotic culture conditions caused a ∼2.6-fold increase of specific ATP formation rates together with a ∼1.7-fold rise in cytosolic and mitochondrial ATP-pools, thus showing increased ATP supply. mRNA expression analysis identified several genes encoding glycosylated proteins with strictly tissue related function. In addition, hyperosmotic culture conditions induced an upregulation of miR-132-3p, miR-132-5p, miR-182, miR-183, miR-194, miR-215-3p, miR-215-5p which have all been related to cell cycle arrest/proliferation in cancer studies. In relation to a previous independent CHO study miR-183 may be the most promising target to enhance qp by stable overexpression. Furthermore, deletion of genes with presumably dispensable function in suspension growing CHO cells may enhance mAB formation by increased ATP levels.

miRNA profiling of high, low and non-producing CHO cells during biphasic fed-batch cultivation reveals process relevant targets for host cell engineering

Fed-batch cultivation of recombinant Chinese hamster ovary (CHO) cell lines is one of the most widely used production modes for commercial manufacturing of recombinant protein therapeutics. Furthermore, fed-batch cultivations are often conducted as biphasic processes where the culture temperature is decreased to maximize volumetric product yields. However, it remains to be elucidated which intracellular regulatory elements actually control the observed pro-productive phenotypes. Recently, several studies have revealed microRNAs (miRNAs) to be important molecular switches of cell phenotypes. In this study, we analyzed miRNA profiles of two different recombinant CHO cell lines (high and low producer), and compared them to a non-producing CHO DG44 host cell line during fed-batch cultivation at 37°C versus a temperature shift to 30°C. Taking advantage of next-generation sequencing combined with cluster, correlation and differential expression analyses, we could identify 89 different miRNAs, which were differentially expressed in the different cell lines and cultivation phases. Functional validation experiments using 19 validated target miRNAs confirmed that these miRNAs indeed induced changes in process relevant phenotypes. Furthermore, computational miRNA target prediction combined with functional clustering identified putative target genes and cellular pathways, which might be regulated by these miRNAs. This study systematically identified novel target miRNAs during different phases and conditions of a biphasic fed-batch production process and functionally evaluated their potential for host cell engineering.

MicroRNA and Embryo Implantation

PROBLEM

In mammals, implantation involves interactions between an activated blastocyst and a receptive endometrium. There are controversies on the role of microRNAs in preimplantation embryo development. The actions of endometrial microRNAs on implantation are beginning to be understood.

METHOD OF STUDY

Review of literature on microRNAs in preimplantation embryos and endometrium.

RESULTS

Emerging evidence suggests a role of microRNAs in blastocyst activation and implantation. Differential expression of microRNAs is found between receptive and non-receptive endometria. Members of the let-7, miR-200, miR-30 families, and the miR-17-92 clusters are more commonly found to be associated with endometrial receptivity. Experimental studies show that the targets of the differentially expressed microRNAs affect endometrial receptivity, decidualization, and embryo implantation. Free and exosome/microvesicle containing microRNAs have been detected in human and ovine uterine luminal fluid (ULF). They may serve as mediators of embryo-endometrium dialog. Some observations suggest that the microRNAs in ULF may be used as biomarkers in infertility treatment.

CONCLUSION

MicroRNAs in endometrium and blastocysts are involved in the implantation process.