Biology subjects

Grosse, G.

Publications and source records attributed to Grosse, G..

4 recordsLinked to original sources

bioRxiv2025

Ischemic stroke induces persistent alteration to brain stromal progenitor cells linked to chronic vascular dysfunction

Fibrotic scar formation after stroke serves a dual role: while essential for providing structural support during post-ischemic recovery, excessive fibrosis in the chronic phase of stroke impairs regenerative processes including axonal regrowth and neovascularization. The temporal dynamics of fibrosis are critical determinants of functional outcomes, as the balance between protective scarring and regenerative capacity differs across distinct stroke phases. Consequently, strategic modulation of fibrotic processes to preserve regenerative potential represents a promising therapeutic approach in stroke recovery. To understand the cellular mechanisms underlying this fibrotic response, we investigated stromal progenitor cell composition in the post-stroke brain. The vast majority of stromal progenitor cells (SPCs) are pericytes, with minorities comprising perivascular fibroblasts (PVFs) and vascular smooth muscle cells. We demonstrate that ischemic stroke drives a long-term shift in this composition, characterized by sustained expansion of the PVF population and excessive laminin deposition in the peri-infarct region, effects that persist for at least six months post-stroke. Single-cell RNA sequencing revealed sustained transcriptional and compositional alterations in the SPC population throughout chronic post-stroke phase, driven by AP-1-mediated signaling via TNF in both PVFs and pericytes. These changes correlate with long-term vasomotor dysfunction and capillary constriction in the peri-infarct region at six weeks post-stroke. Ischemic stroke drives aberrant, persistent PVF accumulation at the capillary bed with implications for post-stroke cerebrovascular dysfunction and recurrent stroke. Taken together, these findings reveal that ischemic stroke drives an aberrant long-term mis-localization of PVFs to the capillary bed that may have clinically-relevant implications for post-stroke cerebrovascular function as well as potential ramifications for recurrent stroke.

neuroscience↗

bioRxiv2022

An update on eukaryotic viruses revived from ancient permafrost

One quarter of the Northern hemisphere is underlain by permanently frozen ground, referred to as permafrost. Due to climate warming, irreversibly thawing permafrost is releasing organic matter frozen for up to a million years, most of which decomposes into carbon dioxide and methane, further enhancing the greenhouse effect. Part of this organic matter also consists of revived cellular microbes (prokaryotes, unicellular eukaryotes) as well as viruses that remained dormant since prehistorical times. While the literature abounds on descriptions of the rich and diverse prokaryotic microbiomes found in permafrost, no additional report about "live" viruses have been published since the two original studies describing pithovirus (in 2014) and mollivirus (in 2015). This wrongly suggests that such occurrences are rare and that "zombie viruses" are not a public health threat. To restore an appreciation closer to reality, we report the preliminary characterizations of 13 new viruses isolated from 7 different ancient Siberian permafrost samples, 1 from the Lena river and 1 from Kamchatka cryosol. As expected from the host specificity imposed by our protocol, these viruses belong to 5 different clades infecting Acanthamoeba spp. but not previously revived from permafrost: Pandoravirus, Cedratvirus, Megavirus, and Pacmanvirus, in addition to a new Pithovirus strain.

microbiology↗

bioRxiv2022

Anaerobic methane oxidizing archaea offset sediment methane concentrations in Arctic thermokarst lagoons

Thermokarst lagoons represent the transition state from a freshwater lacustrine to a marine environment, and receive little attention regarding their role for greenhouse gas production and release in Arctic permafrost landscapes. We studied the fate of methane (CH4) in sediments of a thermokarst lagoon in comparison to two thermokarst lakes on the Bykovsky Peninsula in northeastern Siberia through the analysis of sediment CH4 concentrations and isotopic signature, methane-cycling microbial taxa, sediment geochemistry, and lipid biomarkers. We specifically assessed whether sulfate-driven anaerobic methane oxidation (S-AOM) through anaerobic methanotrophic archaea (ANMEs), common in marine sediments with constant supply of sulfate and methane, establish after thermokarst lagoon development and whether sulfate-driven ANMEs consequently oxidize CH4 that would be emitted to the water column under thermokarst lake conditions. The marine-influenced lagoon environment had fundamentally different methane-cycling microbial communities and metabolic pathways compared to the freshwater lakes, suggesting a substantial reshaping of microbial and carbon dynamics during lagoon formation. Anaerobic sulfate-reducing ANME-2a/2b methanotrophs dominated the sulfate-rich sediments of the lagoon despite its known seasonal alternation between brackish and freshwater inflow. CH4 concentrations in the freshwater-influenced sediments averaged 1.34{+/-}0.98 {micro}mol g-1, with highly depleted {delta}13C-CH4 values ranging from -89{per thousand} to -70{per thousand}. In contrast, the sulfate-affected upper 300 cm of the lagoon exhibited low average CH4 concentrations of 0.011{+/-}0.005 {micro}mol g-1 with comparatively enriched {delta}13C-CH4 values of -54{per thousand} to -37{per thousand} pointing to substantial methane oxidation. Non-competitive methylotrophic methanogens dominated the methanogenic community of the lakes and the lagoon, independent of porewater chemistry and depth. This potentially contributed to the high CH4 concentrations observed in all sulfate-poor sediments. Our study shows that S-AOM in lagoon sediments can effectively reduce sediment CH4 concentrations and we conclude that thermokarst lake to lagoon transitions have the potential to mitigate terrestrial methane fluxes before thermokarst lakes fully transition to a marine environment.

microbiology↗

bioRxiv2021

High prevalence and diversity of beta-lactamase-encoding bacteria in cryosoils and ancient permafrost

BackgroundAntimicrobial resistance is one of the major challenges affecting public health. It is mostly due to the continuous emergence of extended-spectrum {beta}-lactamase from various environments followed by their rapid dissemination and selection in clinical settings. The warming of Earths climate is the other global threat facing human society, in particular with the Arctic regions experiencing a twice faster warming than the global average and permafrost affected by widespread thawing. A potentially dreadful combination of these two threats would be the release and dispersion of harmful microbes that have remained confined to largely uninhabited Arctic regions, or are stored dormant in permafrost. MethodsEnvironmental DNA was isolated from 12 soil samples from various Arctic and subarctic pristine regions in Siberia (Yakutia and Kamchatka), including nine permafrost samples collected at various depths. The large datasets obtained from high throughput sequencing was assembled in contigs and their protein-gene contents predicted. We used exhaustive similarity searches to perform taxonomical assignments of bacterial, archaeal, and eukaryotic organisms, as well as DNA viruses. In addition, we specifically identified {beta}-lactamase genes and their prevalence per bacterial genome estimated through the detection of two universal single copy genes. FindingsA total of 9.217 1011 bp were exploited, leading to a total of 525,313 contigs at least 5kb in size. The DNA content of the various samples was found to be highly variable, not strictly correlated with the depth or radio-carbon-based deposit age, and most likely linked to the global density of microbes trapped in the corresponding permafrost layers. Bacteria account for more than 90% of the contigs in most samples, followed by Eukaryotes and Archaea (always lower than 10%). Viruses represented less than 2% of all contigs in all samples. The taxonomic profiles of surface cryosoils and deep permafrost samples exhibited a high diversity, including between permafrost samples originating from various depths in the same borehole. In all samples, bacterial contigs carrying different {beta}-lactamases from class A to D were identified. InterpretationNo clear common taxonomic feature could be found shared by surface cryosoils or ancient permafrost layers. However, most samples (9/12) exhibited a high frequency of {beta}-lactamase genes, with an estimated average close to 1 copy/bacterial genome. In addition to the well-documented reactivation of infectious ancient pathogens (bacteria, viruses, protozoa), we show now that global warming could contribute to the emergence of new antibiotic resistances through the mobilization by contemporary bacteria of ancient DNA released from thawing permafrost. FundingCNRS PRC research grant (PRC1484-2018) to C.A. E C-F was supported by a PhD grant (DGA/DS/MRIS) #2017 60 0004. GG and JS were funded by ERC PETA-CARB (#338335) and the HGF Impulse and Networking Fund (ERC-0013).

microbiology↗