A comparative study of transfection methods for RNA interference in bone marrow-derived murine dendritic cells

Optimization of a lipid nanoparticle-based protocol for RNA transfection into primary mononuclear phagocytes

The effective delivery of synthetic RNA into mononuclear phagocytes is a prerequisite for experimental research and therapeutic development. However, traditional methods are highly ineffective and toxic for these cells. Here, we aimed to optimize a transfection protocol for primary bone marrow-derived phagocytes, specifically dendritic cells and macrophages, using lipid nanoparticles generated by microfluidics. Our results show that a lipid mixture similar to that used in Moderna's COVID-19 messenger RNA vaccine outperforms the others tested. Improved messenger RNA transfection can be achieved by replacing uridine with methylpseudouridine but not methoxyuridine, which interferes with transfection. The addition of diphenyleneiodonium or apocynin can enhance transfection in a cell type-dependent manner without adverse effects, while apolipoprotein E provides no added value. These optimized transfection conditions can also be used for microRNA agonists and antagonists. In sum, this study offers a straightforward, highly efficient, reproducible, and nontoxic protocol to deliver RNA into different primary mononuclear phagocytes in culture.

Importance of EMT Factor ZEB1 in cDC1 "MutuDC Line" Mediated Induction of Th1 Immune Response

The role of Epithelial to Mesenchymal Transition (EMT) factor Zeb1 is well defined in metastasis and cancer progression but it's importance in dendritic cells (DCs) is unexplored until now. For the first time we report here that Zeb1 controls immunogenic responses of CD8α⁺ conventional Type-I (cDC1) DCs. We found that ZEB1 expression increases significantly after TLR9 stimulation and its depletion impairs activation, co-stimulation and secretion of important cytokines like IL-6, IL-10 and IL-12 in cDC1 MutuDC line. We further confirmed our findings in primary cDC1 DCs derived from bone marrow. Co-culture of these Zeb1 knock down (KD) DCs with OT-II CD4⁺ T helper cells skewed their differentiation toward Th2 subtype. Moreover, adoptive transfer of activated Zeb1 KD DCs cleared intestinal worms in helminth infected mice by increasing Th2 responses in vivo. Integrative genomic analysis showed Zeb1 as an activator of immune response genes in cDC1 MutuDCs as compared to other pathway genes. In addition, differentially regulated genes in Zeb1 KD RNA-seq showed significant enrichment of Th2 activation pathways supporting our in vitro findings. Mechanistically, we showed that decreased IL-12 secreted by Zeb1 KD DCs is the plausible mechanism for increased Th2 differentiation. Collectively our data demonstrate that Zeb1 could be targeted in DCs to modulate T-cell mediated adaptive immune responses.

Cholesterol Modification of p40-Specific Small Interfering RNA Enables Therapeutic Targeting of Dendritic Cells

Small interfering RNA (siRNA)-based therapies allow targeted correction of molecular defects in distinct cell populations. Although efficient in multiple cell populations, dendritic cells (DCs) seem to resist siRNA delivery. Using fluorescence labeling and radiolabeling, we show that cholesterol modification enables siRNA uptake by DCs in vitro and in vivo. Delivery of cholesterol-modified p40 siRNA selectively abolished p40 transcription and suppressed TLR-triggered p40 production by DCs. During immunization with peptide in CFA, cholesterol-modified p40 siRNA generated p40-deficient, IL-10-producing DCs that prevented IL-17/Th17 and IFN-γ/Th1 responses. Only cholesterol-modified p40-siRNA established protective immunity against experimental autoimmune encephalomyelitis and suppressed IFN-γ and IL-17 expression by CNS-infiltrating mononuclear cells without inducing regulatory T cells. Because cholesterol-modified siRNA can thus modify selected DC functions in vivo, it is intriguing for targeted immune therapy of allergic, autoimmune, or neoplastic diseases.

An efficient siRNA-mediated gene silencing in primary human monocytes, dendritic cells and macrophages

Mononuclear phagocytes (MP) comprise monocytes, macrophages (MΦ) and dendritic cells (DC), including their lineage-committed progenitors, which together have an eminent role in health and disease. Lipid-based siRNA-mediated gene inactivation is an established approach to investigate gene function in MP cells. However, although there are few protocols dedicated for siRNA-mediated gene inactivation in primary human DC and MΦ, there are none available for primary human monocytes. Moreover, there is no available method to perform comparative studies of a siRNA-mediated gene silencing in primary monocytes and other MP cells. Here, we describe a protocol optimized for the lipid-based delivery of siRNA to perform gene silencing in primary human blood monocytes, which is applicable to DCs, and differs from the classical route of siRNA delivery into MΦs. Along with this protocol, we provide a comparative analysis of how monocytes, DC and MΦ are efficiently transfected with the target siRNA without affecting cell viability, resulting in strong gene knockdown efficiency, including the simultaneous inactivation of two genes. Moreover, siRNA delivery does not affect classical functions in MP such as differentiation, phagocytosis and migration, demonstrating that this protocol does not induce non-specific major alterations in these cells. As a proof-of-principle, a functional analysis of hematopoietic cell kinase (Hck) shows for the first time that this kinase regulates the protease-dependent migration mode in human monocytes. Collectively, this protocol enables efficient gene inactivation in primary MP, suggesting a wide spectrum of applications such as siRNA-based high-throughput screening, which could ultimately improve our knowledge about MP biology.

Induction of brain microvascular endothelial cell urokinase expression by Cryptococcus neoformans facilitates blood-brain barrier invasion

The invasive ability of the blood-borne fungal pathogen Cryptococcus neoformans can be enhanced through interactions with host plasma components, such as plasminogen. Previously we showed by in vitro studies that plasminogen coats the surface of C. neoformans and is converted to the active serine protease, plasmin, by host plasminogen activators. Viable, but not formaldehyde- or sodium azide-killed, cryptococcal strains undergo brain microvascular endothelial cell-dependent plasminogen-to-plasmin activation, which results in enhanced, plasmin-dependent cryptococcal invasion of primary bovine brain microvascular endothelial cells and fungal ability to degrade plasmin substrates. In the present work, brain microvascular endothelial cells cultured with viable, but not killed, cryptococcal strains led to significant increases in both urokinase mRNA transcription and cell-associated urokinase protein expression. Soluble urokinase was also detected in conditioned medium from brain microvascular endothelial cells cultured with viable, but not killed, C. neoformans. Exposure of plasminogen pre-coated viable C. neoformans to conditioned medium from strain-matched brain microvascular endothelial cell-fungal co-cultures resulted in plasminogen-to-plasmin activation and plasmin-dependent cryptococcal invasion. siRNA-mediated silencing of urokinase gene expression or the use of specific inhibitors of urokinase activity abrogated both plasminogen-to-plasmin activation on C. neoformans and cryptococcal-brain microvascular endothelial cell invasion. Our results suggest that pathogen exploitation of the host urokinase-plasmin(ogen) system may contribute to C. neoformans virulence during invasive cryptococcosis.

Development of an efficient, non-viral transfection method for studying gene function and bone growth in human primary cranial suture mesenchymal cells reveals that the cells respond to BMP2 and BMP3

Background

Achieving efficient introduction of plasmid DNA into primary cultures of mammalian cells is a common problem in biomedical research. Human primary cranial suture cells are derived from the connective mesenchymal tissue between the bone forming regions at the edges of the calvarial plates of the skull. Typically they are referred to as suture mesenchymal cells and are a heterogeneous population responsible for driving the rapid skull growth that occurs in utero and postnatally. To better understand the molecular mechanisms involved in skull growth, and in abnormal growth conditions, such as craniosynostosis, caused by premature bony fusion, it is essential to be able to easily introduce genes into primary bone forming cells to study their function.

Results

A comparison of several lipid-based techniques with two electroporation-based techniques demonstrated that the electroporation method known as nucleofection produced the best transfection efficiency. The parameters of nucleofection, including cell number, amount of DNA and nucleofection program, were optimized for transfection efficiency and cell survival. Two different genes and two promoter reporter vectors were used to validate the nucleofection method and the responses of human primary suture mesenchymal cells by fluorescence microscopy, RT-PCR and the dual luciferase assay. Quantification of bone morphogenetic protein (BMP) signalling using luciferase reporters demonstrated robust responses of the cells to both osteogenic BMP2 and to the anti-osteogenic BMP3.

Conclusions

A nucleofection protocol has been developed that provides a simple and efficient, non-viral alternative method for in vitro studies of gene and protein function in human skull growth. Human primary suture mesenchymal cells exhibit robust responses to BMP2 and BMP3, and thus nucleofection can be a valuable method for studying the potential competing action of these two bone growth factors in a model system of cranial bone growth.

DAP12 promotes IRAK-M expression and IL-10 production by liver myeloid dendritic cells and restrains their T cell allostimulatory ability

Freshly isolated hepatic dendritic cells (DC) are comparatively immature, relatively resistant to maturation, and can downmodulate effector T cell responses. Molecular mechanisms that underlie these properties are ill defined. DNAX-activating protein of 12 kDa (DAP12) is an ITAM-bearing transmembrane adaptor protein that integrates signals through several receptors, including triggering receptor expressed on myeloid cells-1, -2, and CD200R. Notably, DC propagated from DAP12-deficient mice exhibit enhanced maturation in response to TLR ligation. Given the constitutive exposure of liver DC to endotoxin draining from the gut, we hypothesized that DAP12 might regulate liver DC maturation. We show that DAP12 is expressed by freshly isolated liver, spleen, kidney, and lung myeloid DC. Moreover, inhibition of DAP12 expression by liver DC using small interfering RNA promotes their phenotypic and functional maturation, resulting in enhanced TNF-α, IL-6, and IL-12p70 production, reduced secretion of IL-10, and enhanced CD4(+) and CD8(+) T cell proliferation. Furthermore, DAP12 silencing correlates with decreased STAT3 phosphorylation in mature liver DC and with diminished expression of the IL-1R-associated kinase-M, a negative regulator of TLR signaling. These findings highlight a regulatory role for DAP12 in hepatic DC maturation, and suggest a mechanism whereby this function may be induced/maintained.