Biology subjects

Franck, S.

Publications and source records attributed to Franck, S..

4 recordsLinked to original sources

bioRxiv2020

MSH2 knock-down shows CTG repeat stability and concomitant upstream demethylation at the DMPK locus in myotonic dystrophy type 1 human embryonic stem cells

Myotonic dystrophy type 1 (DM1) is caused by expansion of a CTG repeat in the DMPK gene, where expansion size and somatic mosaicism correlates with disease severity and age of onset. While it is known that the mismatch repair protein MSH2 contributes to the unstable nature of the repeat, its role on other disease-related features, such as CpG methylation upstream of the repeat, is unknown. In this study, we investigated the effect of an MSH2 knock-down (MSH2KD) on both CTG repeat dynamics and CpG methylation pattern in human embryonic stem cells (hESC) carrying the DM1 mutation. Repeat size in MSH2 wild type (MSH2WT) and MSH2KD DM1 hESC was determined by PacBio sequencing and CpG methylation by bisulfite massive parallel sequencing. We found stabilization of the CTG repeat concurrent with a gradual loss of methylation upstream of the repeat in MSH2KD cells, while the repeat continued to expand and upstream methylation remained unchanged in MSH2WT control lines. Repeat instability was re-established and biased towards expansions upon MSH2 transgenic re-expression in MSH2KD lines while upstream methylation was not consistently re-established. We hypothesize that the hypermethylation at the mutant DM1 locus is promoted by the MMR machinery and sustained by a constant DNA repair response, establishing a potential mechanistic link between CTG repeat instability and upstream CpG methylation. Our work represents a first step towards understanding how epigenetic alterations and repair pathways connect and contribute to the DM1 pathology.

genetics↗

bioRxiv2020

Endogenous suppression of WNT signalling in human embryonic stem cells leads to low differentiation propensity towards definitive endoderm

SummaryLow differentiation propensity towards a targeted lineage can significantly hamper the utility of individual human pluripotent stem cell (hPSC) lines in biomedical applications. Here, we use monolayer and micropatterned cell cultures, as well as transcriptomic profiling, to investigate how variability in signalling pathway activity between human embryonic stem cell lines affects their differentiation efficiency towards definitive endoderm (DE). We show that endogenous suppression of WNT signalling in hPSCs at the onset of differentiation prevents the switch from self-renewal to DE specification. Gene expression profiling reveals that this inefficient switch is reflected in NANOG expression dynamics. Importantly, we demonstrate that higher WNT stimulation or inhibition of the PI3K/AKT signalling can overcome the DE commitment blockage. Our findings highlight that redirection of the activity of Activin/NODAL pathway by WNT signalling towards mediating DE fate specification is a vulnerable spot, as disruption of this process can result in poor hPSC specification towards DE.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cell biology↗

bioRxiv2020

Constitutional activation of BMP4 and WNT signalling in hESC results in impaired mesendoderm differentiation

We identified a human embryonic stem cell subline that fails to respond to the differentiation cues needed to obtain mesendoderm derivatives, differentiating into trophoblast-like cells instead. RNA-sequencing analysis showed that the subline has hyperactivation of the WNT and BMP4 signalling. Modulation of these pathways with small molecules confirmed them as the cause of the differentiation impairment. While activation of WNT and BMP4 in control cells resulted in a loss of mesendoderm differentiation and induction of trophoblast markers, inhibition of these pathways in the subline restored its ability to differentiate. Karyotyping and exome sequencing analysis did not identify any changes in the genome that could account for the pathway deregulation. These findings add to the increasing evidence that different responses of stem cell lines to differentiation protocols are based on genetic and epigenetic factors, inherent to the line or acquired during cell culture.

cell biology↗

bioRxiv2020

Boosting Toll-like receptor 4 signaling enhances the therapeutic outcome of antibiotic therapy in pneumococcal pneumonia

The emergence and spread of antibiotic resistance emphasize the need for alternative treatment strategies against bacterial infections. Boosting the host innate immunity is not only readily deployable in most individuals but can also mobilize many different antibacterial defenses. This study tested the hypothesis whereby stimulation of the innate immune receptor Toll-like receptor 4 (TLR4) can be combined with antibiotics in the treatment of invasive pneumonia. In a mouse model of Streptococcus pneumoniae infection, a single oral administration of low-dose amoxicillin (AMX) or the systemic delivery of monophosphoryl lipid A (MPLA, a clinically-approved TLR4 activator) decreased the bacterial load in lung and spleen, although this was not sufficient for long-term survival. In contrast, a single treatment with a combination of MPLA and AMX induced significant bacterial clearance with little to no regrowth over time, and was associated with longer survival. Upregulation of genes related to granulocyte infiltration in lung tissue and elevation of blood levels of pro-inflammatory cytokines was immediate and transient in MPLA-treated mice; this indicates activation of the innate immune system in a context of infection. Combination treatment was associated with a well-preserved lung tissue architecture and more rapid recovery from inflammation - suggesting that immune activation by MPLA does not exacerbate pneumonia-induced damage. After AMX administration, plasma AMX concentrations rapidly reached the maximum and declined, whereas the downstream effects of MPLA extended beyond AMX elimination; these findings suggested a two-step effect. Our results demonstrated that leveraging host innate immunity increases the efficacy of antibiotic therapy in bacterial pneumonia.

microbiology↗