Dicer prevents activation of the type I interferon pathway in lipid-loaded macrophages

Background

The expression of the endonuclease Dicer in macrophages decreases atherosclerosis and necrotic core formation by producing microRNAs such as miR-10a. This effect of Dicer is associated with enhanced mitochondrial respiration in lipid-loaded macrophages. However, the mechanism by which Dicer-dependent production of miRNAs in lipid-loaded macrophages regulates mitochondrial function is unclear.

Purpose

We aimed to determine the effect of Dicer on lipid-loaded macrophages in the context of atherosclerosis.

Methods

Mice with a myeloid cell-specific knockout of Dicer (Lys-Cre/Dicerflox/flox/Apoe−/− mice [M-Dicer−/−]) and control mice (Lys-Cre/DicerWT/WT/Apoe−/− mice [M-Dicer+/+]) were fed a high-fat diet (HFD) for 24 weeks. The oxygen consumption rate (OCR) in aortic arch plaques was studied ex vivo by Seahorse Flux XF 24 Analyzer. Bone marrow-derived macrophages (BMDMs) were stimulated with oxLDL (100 μg/mL) for 72 h. Lipid-loaded macrophages were used for proteomic analysis by mass spectrometry. RIP-prime- seq was performed in tAgo2 immunoprecipitates (IP) from Dicer+/+ and Dicer−/− BMDMs. The miRNA expression profile was determined in lipid-loaded BMDMs by NanoString technology. Stat1 phosphorylation was determined in lipid-loaded macrophages by Jess automated western blot system (ProteinSimple).

Result

The OCR in aortic arch tissue with plaques was higher than in those without plaques in M-Dicer+/+ mice after 24 weeks of HFD feeding. Dicer knockout in macrophages decreased the OCR in aortic arch tissues with plaques but not in aortic arch tissues without plaques (n=3–4, p<0.05). The proteomic analysis of oxLDL-treated BMDMs indicated that Dicer knockout activated the type I interferon signaling pathway by up-regulating the expression of STAT1/2 and interferon-stimulated genes, such as ISG15. Proteins related to mitochondrial DNA were upregulated (e.g., Dnmt3a) or downregulated (e.g., Tfam) by Dicer knockout (n=5, adj.p<0.05). RIP-prime-seq from BMDMs showed that 1376 transcripts were significantly enriched in the tAgo IP from Dicer+/+ compared with that from Dicer−/− BMDMs (n=3–5, adj.p<0.05) including Dnmt3a and Stat2. STAT1 phosphorylation was increased in Dicer−/− compared with Dicer+/+ BMDMs. Among the 299 miRNAs downregulated by Dicer knockout in lipid-loaded macrophages (n=6, adj.p<0.05), miR-29 and miR-30 have highly conserved binding sites (predicted by TargetScan) for Dnmt3a.

Conclusion

Our results indicate that Dicer expression in lipid-loaded macrophages limits Stat1/2-driven type I interferon response due to mitochondrial damage. This effect may be mediated by the suppression of Dnmt3a by miRNAs such as miR-29 and miR-30. This suggests that targeting Dnmt3a-mediated mitochondrial damage in lipid-loaded macrophages by miRNAs may be therapeutic strategy to limit atherosclerosis.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG

GPR55 deficiency in B-cells promotes atherosclerosis and regulates plasma cell maturation

 

Atherosclerosis is a chronic and multifactorial disease accompanied by an imbalance between resolving and pro-inflammatory lipid mediators. Targeting lipid signaling might offer new therapeutical targets for improving the clinical outcome in cardiovascular disease patients. We considered lysophosphatidylinositol (LPI) and its receptor G protein-coupled receptor (GPR)55 as a potential modulator of atherosclerosis. Its role in regulating atherosclerosis and B cell function is unknown.

We hypothesize that GPR55 signaling affects atherosclerosis by regulating B cell function.

Atherosclerotic plaques were compared between apolipoprotein-E-deficient (ApoE−/−) and ApoE−/−Gpr55−/− mice after 4 to 16 weeks Western Diet (WD; 0.15% cholesterol; n=12–15 per group). To test the role of B cell GPR55, we generated mixed chimeras by irradiating low density lipoprotein receptor deficient (Ldlr−/−) mice and reconstituting with a mixture of μMT and wildtype or μMT and Gpr55−/− bone marrow cells. Circulating B cells were sorted and bulk RNA sequencing analysis was performed. We performed atheroma plaque characterization, qPCR and ELISA of tissue lysates and measure plasma immunoglobulins. Circulating and tissue leukocyte counts were determined.

We confirmed Gpr55 expression on circulating B cells, which was higher compared to T and myeloid cells. ApoE−/−Gpr55−/− mice had significantly larger plaques after 4 & 16 weeks WD compared to ApoE−/−, with increased body weight & cholesterol levels. In addition, global Gpr55 deficiency resulted in enhanced aortic pro-inflammatory cytokine mRNA expression, a massively upregulated IgG levels and increased counts of splenic germinal center and plasma cells. ApoE−/−Gpr55−/− B-cell RNA-seq analysis showed 460 differential expressed genes compared to ApoE−/−. The main pathways affected were calcium ion transport, immunoglobulin production, T & B cell activation, and cellular response to stress. B cell specific Gpr55 deficiency blunted the metabolic effects but still translated in larger atherosclerotic plaques and elevated plasma IgG levels.

Both global and B cell-restricted Gpr55 deficiency promotes atherosclerosis and is associated with a pro-inflammatory phenotype.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): The authors received funds from the Deutsche Forschungsgemeinschaft (STE1053/6-1, STE1053/8-1 to S.S. and SFB1123 to S.S., C.W. and L.M.), the German Ministry of Research and Education (DZHK FKZ 81Z0600205 to S.S.) and the LMU Medical Faculty FöFoLe program (1061 to R.G.P.). I.H. is supported by the DFG (HI1573/2 and CRC1425 #422681845).

Heterogeneity of neurons reprogrammed from spinal cord astrocytes by the proneural factors Ascl1 and Neurogenin2

Astrocytes are a viable source for generating new neurons via direct conversion. However, little is known about the neurogenic cascades triggered in astrocytes from different regions of the CNS. Here, we examine the transcriptome induced by the proneural factors Ascl1 and Neurog2 in spinal cord-derived astrocytes in vitro. Each factor initially elicits different neurogenic programs that later converge to a V2 interneuron-like state. Intriguingly, patch sequencing (patch-seq) shows no overall correlation between functional properties and the transcriptome of the heterogenous induced neurons, except for K-channels. For example, some neurons with fully mature electrophysiological properties still express astrocyte genes, thus calling for careful molecular and functional analysis. Comparing the transcriptomes of spinal cord- and cerebral-cortex-derived astrocytes reveals profound differences, including developmental patterning cues maintained in vitro. These relate to the distinct neuronal identity elicited by Ascl1 and Neurog2 reflecting their developmental functions in subtype specification of the respective CNS region.

Modification of histone 3 lysine 27 (H3K27) trimethylation in EZH2 and JMJD3 deficient T cells attenuates atherosclerosis through polarization towards anti-inflammatory phenotypes

Background

The trimethylation status of Histone 3 Lysine 27 (H3K27), which is regulated by the methylating enzyme Enchancer of zeste homolog 2 (EZH2) and the demethylating enzyme Jumonji domain containing 3 (JMJD3), is a critical epigenetic signature for the differentiation and polarization of T cells. During atherogenesis, T cells initiate and propagate lesion formation through imbalanced polarization of T helper (Th) cells leading to the accumulation of pro-atherogenic T cell subsets, including Th1, that exacerbate inflammation.

Purpose

We hypothesize that T-cell EZH2 and JMJD3 may contribute to inflammation and atherosclerotic plaque formation through opposing polarization of T helper cells.

Methods

We generated transgenic mice with either Ezh2 or Jmjd3 flanked by loxP-sites that were sensitive to Cre-mediated inactivation. Mice were backcrossed to apolipoprotein E (ApoE−/−) mice expressing Cre in T cells (Cd4Cretg) to generate hypercholesterolemic Ezh2fl/fl-Cd4Cre-ApoE−/− (Ezh2fl/fl) and Jmjd3fl/fl-Cd4Cre-ApoE−/− (Jmjd3fl/fl) mice. Following a 6 week high fat diet, the immune status and atherosclerotic progression of the mice were assessed by histology, flow cytometry, and RNA sequencing.

Results

Mass spectrometry of histones isolated from CD4+ T cells confirmed a decrease in H3K27 trimethylation in Ezh2fl/fl mice and an increase in Jmjd3fl/fl mice (p=0.0002 and p=0.01, respectively). In the aortic root, both Ezh2fl/fl and Jmjd3fl/fl mice developed significantly less atherosclerosis (p=0.001 and p=0.0006, respectively). A shift from naive T cells to effectors was observed in the lymph nodes and spleens in both models (p<0.0001 for all). Flow cytometric analysis revealed a systemic accumulation of Th2 in Ezh2fl/flmice (p<0.0001), which was corroborated by a 2.75 log2 fold change of IL-4 expression (padj<0.0001) (RNA-sequencing) in CD4+ T cells as well as elevated IL-4 plasma concentrations (p=0.04). Ingenuity pathway analysis revealed the canonical Th1 pathway was inhibited in Ezh2fl/fl mice. In Jmjd3fl/fl mice, flow cytometric analysis revealed a 2 fold increase of Foxp3-expressing T regulatory (Treg) cells in the blood (p=0.005), lymph nodes (p<0.0001), and spleen (p<0.0001).

Conclusions

Our data demonstrate deficiency of either EZH2 or JMJD3 strongly reduce lesion progression in atherosclerosis through polarization of T cells towards anti-atherogenic Th2 or Treg populations, respectively. Targeting T-cell H3K27 trimethylation may be a promising candidate for further investigation to treat atherosclerosis.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): German Research Foundation (DFG)

A humanized version of Foxp2 does not affect ultrasonic vocalization in adult mice

The transcription factor FOXP2 has been linked to severe speech and language impairments in humans. An analysis of the evolution of the FOXP2 gene has identified two amino acid substitutions that became fixed after the split of the human and chimpanzee lineages. Studying the functional consequences of these two substitutions in the endogenous Foxp2 gene of mice showed alterations in dopamine levels, striatal synaptic plasticity, neuronal morphology and cortico-striatal-dependent learning. In addition, ultrasonic vocalizations (USVs) of pups had a significantly lower average pitch than control littermates. To which degree adult USVs would be affected in mice carrying the 'humanized' Foxp2 variant remained unclear. In this study, we analyzed USVs of 68 adult male mice uttered during repeated courtship encounters with different females. Mice carrying the Foxp2(hum/hum) allele did not differ significantly in the number of call elements, their element structure or in their element composition from control littermates. We conclude that neither the structure nor the usage of USVs in adult mice is affected by the two amino acid substitutions that occurred in FOXP2 during human evolution. The reported effect for pup vocalization thus appears to be transient. These results are in line with accumulating evidence that mouse USVs are hardly influenced by vocal learning. Hence, the function and evolution of genes that are necessary, but not sufficient for vocal learning in humans, must be either studied at a different phenotypic level in mice or in other organisms.

Humanized Foxp2 specifically affects cortico-basal ganglia circuits

It has been proposed that two amino acid substitutions in the transcription factor FOXP2 have been positively selected during human evolution and influence aspects of speech and language. Recently it was shown that when these substitutions are introduced into the endogenous Foxp2 gene of mice, they increase dendrite length and long-term depression (LTD) in medium spiny neurons of the striatum. Here we investigated if these effects are found in other brain regions. We found that neurons in the cerebral cortex, the thalamus and the striatum have increased dendrite lengths in the humanized mice whereas neurons in the amygdala and the cerebellum do not. In agreement with previous work we found increased LTD in medium spiny neurons, but did not detect alterations of synaptic plasticity in Purkinje cells. We conclude that although Foxp2 is expressed in many brain regions and has multiple roles during mammalian development, the evolutionary changes that occurred in the protein in human ancestors specifically affect brain regions that are connected via cortico-basal ganglia circuits.

LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia

Left-right asymmetrical brain function underlies much of human cognition, behavior and emotion. Abnormalities of cerebral asymmetry are associated with schizophrenia and other neuropsychiatric disorders. The molecular, developmental and evolutionary origins of human brain asymmetry are unknown. We found significant association of a haplotype upstream of the gene LRRTM1 (Leucine-rich repeat transmembrane neuronal 1) with a quantitative measure of human handedness in a set of dyslexic siblings, when the haplotype was inherited paternally (P=0.00002). While we were unable to find this effect in an epidemiological set of twin-based sibships, we did find that the same haplotype is overtransmitted paternally to individuals with schizophrenia/schizoaffective disorder in a study of 1002 affected families (P=0.0014). We then found direct confirmatory evidence that LRRTM1 is an imprinted gene in humans that shows a variable pattern of maternal downregulation. We also showed that LRRTM1 is expressed during the development of specific forebrain structures, and thus could influence neuronal differentiation and connectivity. This is the first potential genetic influence on human handedness to be identified, and the first putative genetic effect on variability in human brain asymmetry. LRRTM1 is a candidate gene for involvement in several common neurodevelopmental disorders, and may have played a role in human cognitive and behavioral evolution.