Benznidazole (BZ) is the most commonly used drug for the treatment of Chagas disease. Although BZ is known to induce the formation of free radicals and electrophilic metabolites within the parasite Trypanosoma cruzi, its precise mechanisms of action are still elusive. Here, we analyzed the survival of T. cruzi exposed to BZ using genetically modified parasites overexpressing different DNA repair proteins. Our results indicate that BZ induces oxidation mainly in the nucleotide pool, as heterologous expression of the nucleotide pyrophosphohydrolase MutT (but not overexpression of the glycosylase TcOgg1) increased drug resistance in the parasite. In addition, electron microscopy indicated that BZ catalyzes the formation of double-stranded breaks in the parasite, as its genomic DNA undergoes extensive heterochromatin unpacking following exposure to the drug. Furthermore, the overexpression of proteins involved in the recombination-mediated DNA repair increased resistance to BZ, reinforcing the idea that the drug causes double-stranded breaks. Our results also show that the overexpression of mitochondrial DNA repair proteins increase parasite survival upon BZ exposure, indicating that the drug induces lesions in the mitochondrial DNA as well. These findings suggest that BZ preferentially oxidizes the nucleotide pool, and the extensive incorporation of oxidized nucleotides during DNA replication leads to potentially lethal double-stranded DNA breaks in T. cruzi DNA.
Mesenchymal stem/stromal cells (MSCs) are promising tools in cell therapy. They secrete extracellular vesicles (EVs) that carry different classes of molecules that can promote skin repair, but the mechanisms are poorly understood. Skin wound healing is a complex process that requires the activity of several signaling pathways and cell types, including keratinocytes and fibroblasts. In this study, we explored whether adipose tissue MSC-derived EVs could accelerate migration and proliferation of keratinocytes and fibroblasts, activate the AKT pathway, and promote wound healing in vivo. Furthermore, we evaluated if EV effects are miR-205 dependent. We found that MSC EVs had an average diameter of 135 nm. Keratinocytes and fibroblasts exposed to EVs exhibited higher levels of proliferation, migration, and AKT activation. Topical administration of EVs accelerated skin wound closure. Knockdown of miR-205 decreased AKT phosphorylation in fibroblasts and keratinocytes, whereas migration was decreased only in keratinocytes. Moreover, knockdown of miR-205 failed to inhibit AKT phosphorylation in fibroblasts and keratinocytes exposed to EVs. About the mechanism of EV effects, we found that incubation with EVs prevented inhibition of AKT activation by miR-205 knockdown, suggesting that EVs activate AKT independently of miR-205. In conclusion, we demonstrated that EVs are a promising tool for wound healing.
The oxidative lesion 8-oxoguanine (8-oxoG) is removed during base excision repair by the 8-oxoguanine DNA glycosylase 1 (Ogg1). This lesion can erroneously pair with adenine, and the excision of this damaged base by Ogg1 enables the insertion of a guanine and prevents DNA mutation. In this report, we identified and characterized Ogg1 from the protozoan parasite Trypanosoma cruzi (TcOgg1), the causative agent of Chagas disease. Like most living organisms, T. cruzi is susceptible to oxidative stress, hence DNA repair is essential for its survival and improvement of infection. We verified that the TcOGG1 gene encodes an 8-oxoG DNA glycosylase by complementing an Ogg1-defective Saccharomyces cerevisiae strain. Heterologous expression of TcOGG1 reestablished the mutation frequency of the yeast mutant ogg1−/− (CD138) to wild type levels. We also demonstrate that the overexpression of TcOGG1 increases T. cruzi sensitivity to hydrogen peroxide (H2O2). Analysis of DNA lesions using quantitative PCR suggests that the increased susceptibility to H2O2 of TcOGG1-overexpressor could be a consequence of uncoupled BER in abasic sites and/or strand breaks generated after TcOgg1 removes 8-oxoG, which are not rapidly repaired by the subsequent BER enzymes. This hypothesis is supported by the observation that TcOGG1-overexpressors have reduced levels of 8-oxoG both in the nucleus and in the parasite mitochondrion. The localization of TcOgg1 was examined in parasite transfected with a TcOgg1-GFP fusion, which confirmed that this enzyme is in both organelles. Taken together, our data indicate that T. cruzi has a functional Ogg1 ortholog that participates in nuclear and mitochondrial BER.
Edited by Roger J. Colbran Calcium (Ca 2؉ ) signaling within the cell nucleus regulates specific cellular events such as gene transcription and cell proliferation. Nuclear and cytosolic Ca 2؉ levels can be independently regulated, and nuclear translocation of receptor tyrosine kinases (RTKs) is one way to locally activate signaling cascades within the nucleus. Nuclear RTKs, including the epidermal growth factor receptor (EGFR), are important for processes such as transcriptional regulation, DNA-damage repair, and cancer therapy resistance. RTKs can hydrolyze phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) within the nucleus, leading to Ca 2؉ release from the nucleoplasmic reticulum by inositol 1,4,5-trisphosphate receptors. PI(4,5)P 2 hydrolysis is mediated by phospholipase C (PLC). However, it is unknown which nuclear PLC isoform is triggered by EGFR. Here, using subcellular fractionation, immunoblotting and fluorescence, siRNA-based gene knockdowns, and FRET-based biosensor reporter assays, we investigated the role of PLC␦4 in epidermal growth factor (EGF)-induced nuclear Ca 2؉ signaling and downstream events. We found that EGF-induced Ca 2؉ signals are inhibited when translocation of EGFR is impaired. Nuclear Ca 2؉ signals also were reduced by selectively buffering inositol 1,4,5trisphosphate (InsP 3 ) within the nucleus. EGF induced hydrolysis of nuclear PI(4,5)P 2 by the intranuclear PLC␦4, rather than by PLC␥1. Moreover, protein kinase C, a downstream target of EGF, was active in the nucleus of stimulated cells. Furthermore, PLC␦4 and InsP 3 modulated cell cycle progression by regulating the expression of cyclins A and B1. These results provide evidence that EGF-induced nuclear signaling is mediated by nuclear PLC␦4 and suggest new therapeutic targets to modulate the proliferative effects of this growth factor.
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