MicroRNA 34a promotes ionizing radiation-induced DNA damage repair in murine hematopoietic stem cells

Inhibition of Foxp3 expression in the placenta of mice infected intraperitoneally by toxoplasma gondii tachyzoites: insights into the PPARγ/miR-7b-5p/Sp1 signaling pathway

BACKGROUND

Toxoplasma gondii, an obligate intracellular parasitic protozoa, infects approximately 30% of the global population. Contracting T. gondii at the primary infection of the mother can result in neonatal microcephaly, chorioretinitis, hydrocephalus, or mortality. Our previous study indicated that pregnant mice infected with T. gondii displayed a decrease in both the number and the suppressive ability of regulatory T cells, accompanied by the reduced Forkhead box P3 (Foxp3). Numerous studies have proved that microRNAs (miRNAs) are implicated in T. gondii infection, but there is meager evidence on the relationship between alterations of miRNAs and downregulation of Foxp3 induced by T. gondii.

METHODS

Quantitative reverse transcription polymerase chain reaction was utilized to detect the transcriptions of miRNAs and Foxp3. Protein blotting and immunofluorescence were used to detect the expressions of Foxp3 and related transcription factors. The structure of mouse placenta was observed by hematoxylin and eosin (HE) staining. To examine the activity of miR-7b promoter and whether miR-7b-5p targets Sp1 to suppress Foxp3 expression, we constructed recombinant plasmids containing the full-length/truncated/mutant miR-7b promoter sequence or wildtype/mutant of Sp1 3' untranslated region (3' UTR) to detect the fluorescence activity in EL4 cells.

RESULTS

In T. gondii-infected mice, miR-7b transcription was significantly elevated, while Foxp3 expression was decreased in the placenta. In vitro, miR-7b mimics downregulated Foxp3 expression, whereas its inhibitors significantly upregulated Foxp3 expression. miR-7b promoter activity was elevated upon the stimulation of T. gondii antigens, which was mitigated by co-transfection of mutant miR-7b promoter lacking peroxisome proliferator-activated receptor γ (PPARγ) target sites. Additionally, miR-7b mimics diminished Sp1 expression, while miR-7b inhibitors elevated its expression. miR-7b mimics deceased the fluorescence activity of Sp1 3' untranslated region (3' UTR), but it failed to impact the fluorescence activity upon the co-transfection of mutant Sp1 3' UTR lacking miR-7b target site.

CONCLUSIONS

T. gondii infection and antigens promote miR-7b transcription but inhibit Foxp3 protein and gene levels. T. gondii antigens promote miR-7b promoter activity by a PPARγ-dependent mechanism. miR-7b directly binds to Sp1 3' UTR to repress Sp1 expression. Understanding the regulatory functions by which T. gondii-induced miR-7b suppresses Foxp3 expression can provide new perspectives for the possible therapeutic avenue of T. gondii-induced adverse pregnancy outcomes.

Melanocortin/MC5R axis regulates the proliferation of hematopoietic stem cells in mice after ionizing radiation injury

Hematopoietic stem cells (HSCs) possess great self-renewal and multidirectional differentiation abilities, which contribute to the continuous generation of various blood cells. Although many intrinsic and extrinsic factors have been found to maintain HSC homeostasis, the precise regulation of hematopoiesis under stress conditions is poorly understood. In this study, we show that melanocortin receptor 5 (MC5R) is abundantly expressed in hematopoietic stem progenitor cells (HSPCs). Using an MC5R knockout mouse model, we observed that it is not essential for steady-state hematopoiesis. Interestingly, the levels of α-melanocyte stimulating hormone (α-MSH), an important subtype of melanocortin, were elevated in the serum and bone marrow, and the expression of MC5R was upregulated in HSPCs from mice after irradiation. MC5R deficiency aggravates irradiation-induced myelosuppression because of impaired proliferation and reconstitution of HSCs. Further investigation revealed that the melanocortin/MC5R axis regulates the proliferation of HSCs by activating the PI3K/AKT and MAPK pathways. More importantly, α-MSH treatment can significantly accelerate hematopoietic recovery in irradiated mice. In conclusion, our data demonstrate that the melanocortin/MC5R axis plays a crucial role in regulating HSC proliferation under stress, thus providing a promising strategy to promote hematopoietic regeneration when suffering from injury.

Protection of the hematopoietic system against radiation-induced damage: drugs, mechanisms, and developments

Sometimes, people can be exposed to moderate or high doses of radiation accidentally or through the environment. Radiation can cause great harm to several systems within organisms, especially the hematopoietic system. Several types of drugs protect the hematopoietic system against radiation damage in different ways. They can be classified as "synthetic drugs" and "natural compounds." Their cellular mechanisms to protect organisms from radiation damage include free radical-scavenging, anti-oxidation, reducing genotoxicity and apoptosis, and alleviating suppression of the bone marrow. These topics have been reviewed to provide new ideas for the development and research of drugs alleviating radiation-induced damage to the hematopoietic system.

Key miRNAs and Genes in the High-Altitude Adaptation of Tibetan Chickens

Tibetan chickens living at high altitudes show specific physiological adaptations to the extreme environmental conditions. However, the regulated base of how chickens adapt to high-altitude habitats remains largely unknown. In this study, we sequenced 96 transcriptomes (including 48 miRNA and 48 mRNA transcriptomes of heart, liver, lung, and brain) and resequenced 12 whole genomes of Tibetan chickens and Peng'xian yellow chickens. We found that several miRNAs show the locally optimal plastic changes that occurred in miRNAs of chickens, such as miR-10c-5p, miR-144-3p, miR-3536, and miR-499-5p. These miRNAs could have effects on early adaption to the high-altitude environment of chickens. In addition, the genes under selection between Tibetan chickens and Peng'xian yellow chickens were mainly related to oxygen transport and oxidative stress. The I-kappa B kinase/NF-kappa B signaling pathway is widely found for high-altitude adaptation in Tibetan chickens. The candidate differentially expressed miRNAs and selected genes identified in this study may be useful in current breeding efforts to develop improved breeds for the highlands.

The Role of MicroRNA in DNA Damage Response

DNA is essential for the development and function of organisms. A number of factors affect DNA integrity and cause DNA damages, such as ultraviolet light, ionizing radiation and hydrogen peroxide. DNA damages activate a series of intracellular reactions, called DNA damage response, which play a crucial role in the pathogenesis of cancers and other diseases. MiRNA is a type of evolutionarily conserved non-coding RNA and affects the expression of target genes by post-transcriptional regulation. Increasing evidences suggested that the expression of some miRNAs was changed in tumor cases. MiRNAs may participate in DNA damage response and affect genomic stability via influencing the processes of cell cycle, DNA damage repair and apoptosis, thus ultimately impact on tumorigenesis. Therefore, the role of miRNA in DNA damage response is reviewed, to provide a theoretical basis for the mechanism of miRNAs’ effects on DNA damage response and for the research of new therapies for diseases.

CD63 acts as a functional marker in maintaining hematopoietic stem cell quiescence through supporting TGFβ signaling in mice

Hematopoietic stem cell (HSC) fate is tightly controlled by various regulators, whereas the underlying mechanism has not been fully uncovered due to the high heterogeneity of these populations. In this study, we identify tetraspanin CD63 as a novel functional marker of HSCs in mice. We show that CD63 is unevenly expressed on the cell surface in HSC populations. Importantly, HSCs with high CD63 expression (CD63^hi) are more quiescent and have more robust self-renewal and myeloid differentiation abilities than those with negative/low CD63 expression (CD63^-/lo). On the other hand, using CD63 knockout mice, we find that loss of CD63 leads to reduced HSC numbers in the bone marrow. In addition, CD63-deficient HSCs exhibit impaired quiescence and long-term repopulating capacity, accompanied by increased sensitivity to irradiation and 5-fluorouracil treatment. Further investigations demonstrate that CD63 is required to sustain TGFβ signaling activity through its interaction with TGFβ receptors I and II, thereby playing an important role in regulating the quiescence of HSCs. Collectively, our data not only reveal a previously unrecognized role of CD63 but also provide us with new insights into HSC heterogeneity.

Grape seed proanthocyanidin extract ameliorates ionizing radiation-induced hematopoietic stem progenitor cell injury by regulating Foxo1 in mice

Ionizing radiation (IR)-induced excessive reactive oxygen species (ROS) is an important contributor of the injury of hematopoietic system. Grape seed proanthocyanidin extract (GSPE) is a new type of antioxidant, whereas whether it could ameliorate IR-induced hematopoietic injury remains unclear. Here, we show that GSPE treatment improves the survival of irradiated mice and alleviates IR-induced myelosuppression. Meanwhile, the hematopoietic reconstituting ability of hematopoietic stem cells (HSCs) in mice following irradiation exposure is significantly increased after GSPE treatment. Furthermore, GSPE treatment can reduce IR-induced ROS production and relieve DNA damage and apoptosis in hematopoietic stem progenitor cells (HSPCs). Interestingly, we find that a critical antioxidant-associated gene fokhead box transcription factor O1 (Foxo1) is significantly decreased in HSPCs after irradiation. Consistently, hematopoietic specific deletion of Foxo1 increases the radiosensitivity of mice. Further investigations reveal that GSPE treatment specifically upregulates the expression of Foxo1, as well as its target genes superoxide dismutase 1 (SOD1), superoxide dismutase 2 (SOD2) and catalase (CAT). Importantly, Foxo1 deficiency largely abolishes the radioprotection of GSPE on HSPCs. Collectively, our data demonstrate that GSPE plays an important role in ameliorating IR-induced HSPC injury via the Foxo1-mediated pathway. Therefore, GSPE may be used as a promising radioprotective agent.

Micro-RNAs: A safety net to protect hematopoietic stem cell self-renewal

The hematopoietic system is sustained over time by a small pool of hematopoietic stem cells (HSCs). They reside at the apex of a complex hierarchy composed of cells with progressively more restricted lineage potential, regenerative capacity, and with different proliferation characteristics. Like other somatic stem cells, HSCs are endowed with long-term self-renewal and multipotent differentiation ability, to sustain the high turnover of mature cells such as erythrocytes or granulocytes, and to rapidly respond to acute peripheral stresses including bleeding, infections, or inflammation. Maintenance of both attributes over time, and of the proper balance between these opposite features, is crucial to ensure the homeostasis of the hematopoietic system. Micro-RNAs (miRNAs) are short non-coding RNAs that regulate gene expression posttranscriptionally upon binding to specific mRNA targets. In the past 10 years they have emerged as important players for preserving the HSC pool by acting on several biological mechanisms, such as maintenance of the quiescent state while preserving proliferation ability, prevention of apoptosis, premature differentiation, lineage skewing, excessive expansion, or retention within the BM niche. miRNA-mediated posttranscriptional fine-tuning of all these processes constitutes a safety mechanism to protect HSCs, by complementing the action of transcription factors and of other regulators and avoiding unwanted expansion or aplasia. The current knowledge of miRNAs function in different aspects of HSC biology, including consequences of aberrant miRNA expression, will be reviewed; yet unsolved issues will be discussed. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development.

MicroRNA-21 maintains hematopoietic stem cell homeostasis through sustaining the NF-κB signaling pathway in mice

Long-term hematopoietic output is dependent on hematopoietic stem cell (HSC) homeostasis which is maintained by a complex molecular network in which microRNA play crucial roles, although the underlying molecular basis has not been fully elucidated. Here we show that microRNA-21 (miR-21) is enriched in murine HSC, and that mice with conditional knockout of miR-21 exhibit an obvious perturbation in hematopoiesis. Moreover, significant loss of HSC quiescence and long-term reconstituting ability are observed in the absence of miR-21. Further studies revealed that miR-21 deficiency markedly decreases the nuclear factor kappa B (NF-B) pathway, accompanied by increased expression of PDCD4, a direct target of miR-21, in HSC. Interestingly, overexpression of PDCD4 in wild-type HSC generates similar phenotypes as those of miR-21-deficient HSC. More importantly, knockdown of PDCD4 can significantly rescue the attenuation of NF-B activity, thereby improving the defects in miR-21-null HSC. On the other hand, we found that miR-21 is capable of preventing HSC from ionizing radiation- induced DNA damage via activation of the NF-B pathway. Collectively, our data demonstrate that miR-21 is involved in maintaining HSC homeostasis and function, at least in part, by regulating the PDCD4-mediated NF-B pathway and provide a new insight into radioprotection of HSC.

MicroRNA-34a deficiency leads to impaired wound closure by augmented inflammation in mice

Background

Proper inflammation resolution is critical for cutaneous wound healing and disordered inflammation resolution results in chronic nonhealing wounds. However, the cellular and molecular mechanisms for resolution of inflammation during skin wound healing are not well understood. MicroRNA-34a is regarded as one tumor suppressor with complexed immune regulatory effects, yet its role during skin wound repair is still unclear.

Methods

Circular full thickness excisional wounds were made on the dorsal skin of C57 mice and miR-34a expression pattern was examined by real time RT-PCR and in situ hybridization. The wound healing rates and histologic morphometric analysis were quantified and compared between wounds treated with antagomir-34a and autologous control antagomir-NC wounds, as well as wounds between miR-34a knockout (KO) and wild type (WT) mice. Immunohistochemistry (IHC) for both MPO and F4/80 were performed to examine the infiltrative neutrophils and macrophages in wounds from miR-34a KO and WT mice. Cytokines including IL-1β, IL-6, TNF-α and IL-10, were detected and analyzed by real time RT-PCR during wound healing. IHC for IL-6 and p-STAT3 were quantified, and WB for p-STAT3 and IL-6R were examined in wounds of miR-34a KO and WT mice.

Results

We found miR-34a was significantly downregulated in the inflammatory phase and back to normal levels in the proliferative phase. Both topical knockdown wounds miR-34a levels by antagomir gel and systematic knockout miR-34a using KO mice resulted in impaired wound healing with delayed re-epithelialization and augmented inflammation. IHC results indicated that there were more residual infiltrative inflammatory cells in the proliferative phase. Moreover, over-activated IL-6/STAT3 signal pathway was identified in the wounds of miR-34a KO mice.

Conclusions

Our findings reveal that miR-34a deficiency augments skin wound inflammation response and leads to impaired wound healing, which suggest that targeted inhibition of miR-34a for tissue repair/regeneration should be with serious consideration.