Biology subjects

Helbling, P. M.

Publications and source records attributed to Helbling, P. M..

4 recordsLinked to original sources

bioRxiv2023

Tissue-scale dynamic mapping of Hematopoietic Stem Cells and supportive niche cells in the fetal liver

The fetal liver (FL) plays a fundamental role in the ontogeny of the hematopoietic system, by transiently providing a fertile microenvironment for the maturation, proliferation and expansion of fetal hematopoietic progenitors, as well as definitive hematopoietic stem cells (HSCs). Nonetheless, the cellular make up and identity of HSC niches in the FL remain poorly described. Here we employed a combination of 3D quantitative microscopy, bulk mRNA-seq, flow cytometry and cell-specific reporter models, to dissect the spatiotemporal dynamics of putative niche cells and HSCs in the FL microenvironment. We find that at peak stages of FL hematopoiesis, pro-hematopoietic cytokines are promiscuously expressed by endothelial, mesenchymal cells and most prominently by hepatoblasts. These multicellular consortia of parenchymal/stromal cells are spatially predominant in the FL, thus providing unrestricted access to supportive factors throughout the entire tissue. Accordingly, in these early phases HSCs are found scattered across the parenchyma not displaying obvious spatial biases within the broad microanatomy of the FL, but exhibiting clustering behaviors. This highly conducive microenvironment is transient and gets rapidly remodeled through hepatoblast differentiation and sterile inflammatory signaling, leading to the downregulation of hematopoietic factors and the contraction of supportive niches, which temporarily coincide with the exit of HSCs towards emergent BM tissues.

developmental biology↗

bioRxiv2020

CD8 T cells induce destruction of bone marrow stromal niches and hematopoietic stem cell dysfunction in chronic viral infections

Chronic viral infections are associated with hematopoietic suppression and bone marrow (BM) failure, which have been linked to hematopoietic stem cell (HSC) exhaustion. However, how persistent viral infectious challenge and ensuing inflammatory responses target BM tissues and perturb hematopoietic homeostasis remains poorly understood. Here, we combine extensive functional analyses with advanced 3D microscopy to demonstrate that chronic infection with lymphocytic choriomeningitis virus clone 13 results in the long-term impairment of HSC function, concomitant with a persistent destruction of the HSC-supportive stromal networks of mesenchymal CXCL12-abundant reticular cells. During infections, long lasting injuries and aberrant transcriptional programs of the stromal infrastructure diminish the capacity of the BM microenvironment to adequately support HSC maintenance. Mechanistically, BM immunopathology is elicited by virus-specific, activated CD8 T cells, which accumulate in the BM via interferon-dependent mechanisms. Combined inhibition of type I and II IFN pathways completely preempts viral-mediated degeneration of CARc networks and protects HSCs from persistent dysfunction. Hence, viral infections and ensuing immune reactions chronically interfere with BM function by disrupting essential stromal-derived, hematopoietic-supporting cues.

immunology↗

bioRxiv2019

Global transcriptomic profiling of the bone marrow stromal microenvironment during postnatal development, aging and inflammation

Bone marrow (BM) stromal cells provide the structural and regulatory framework for hematopoiesis and contribute to developmental-stage specific niches, such as those preserving hematopoietic stem cell (HSCs). Despite recent advances in our understanding of stromal composition and function, little is known on the dynamic transcriptional remodeling that this compartment undergoes over time and during adaptation to stress. Similarly, how molecular changes in stroma are linked to age-related modulation of hematopoiesis is poorly understood. Using RNA-sequencing, we performed a longitudinal comparison of the transcriptional profile of four principal mesenchymal and endothelial stromal subsets, namely CXCL12-abundant reticular (CARc), PDGFR-+Sca-1+, sinusoidal (SECs) and arterial endothelial cells (AECs), isolated from early postnatal, adult and aged mice. Our data i) provide molecular fingerprints defining novel, cell-specific anatomical and functional features ii) reveal radical reprogramming of pro-hematopoietic, immune and matrisomic transcriptional programs during the narrow temporal transition from juvenile to adult stages iii) demonstrate that homeostatic aging is characterized by a progressive and pronounced upregulation of pro-inflammatory gene-expression and loss of stromal cell fitness. By profiling in vivo responses of stromal cells to infection-mimicking agents, we finally demonstrate that transcriptomic pathways elicited by sterile inflammation are largely recapitulated during aging, thereby supporting the inflammatory basis of aging-related adaptations of BM hematopoietic function.

immunology↗

bioRxiv2019

Combined single-cell and spatial transcriptomics reveals the molecular, cellular and spatial bone marrow niche organization

The bone marrow (BM) constitutes the primary site for life-long blood production and skeletal regeneration. However, its cellular composition and the spatial organization into distinct niches remains controversial. Here, we combine single-cell and spatially resolved transcriptomics to systematically map the molecular and cellular composition of the endosteal, sinusoidal, and arteriolar BM niches. This allowed us to transcriptionally profile all major BM resident cell types, determine their localization, and clarify the cellular and spatial sources of key growth factors and cytokines. Our data demonstrate that previously unrecognized Cxcl12-abundant reticular (CAR) cell subsets (i.e. Adipo- and Osteo-CAR cells) differentially localize to sinusoidal or arteriolar surfaces, locally act as professional cytokine secreting cells, and thereby establish distinct peri-vascular micro-niches. Importantly, we also demonstrate that the 3-dimensional organization of the BM can be accurately inferred from single-cell gene expression data using the newly developed RNA-Magnet algorithm. Together, our study reveals the cellular and spatial organization of BM niches, and offers a novel strategy to dissect the complex organization of whole organs in a systematic manner.\n\nOne Sentence SummaryIntegration of single-cell and spatial transcriptomics reveals the molecular, cellular and spatial organization of bone marrow niches

developmental biology↗