Nod1-dependent NF-kB activation initiates hematopoietic stem cell specification in response to small Rho GTPases

NF-κB-mediated developmental delay extends lifespan in Drosophila

Developmental time (or time to maturity) strongly correlates with an animal's maximum lifespan, with late-maturing individuals often living longer. However, the genetic mechanisms underlying this phenomenon remain largely unknown. This may be because most previously identified longevity genes regulate growth rate rather than developmental time. To address this gap, we genetically manipulated prothoracicotropic hormone (PTTH), the primary regulator of developmental timing in Drosophila, to explore the genetic link between developmental time and longevity. Loss of PTTH delays developmental timing without altering the growth rate. Intriguingly, PTTH mutants exhibit extended lifespan despite their larger body size. This lifespan extension depends on ecdysone signaling, as feeding 20-hydroxyecdysone to PTTH mutants reverses the effect. Mechanistically, loss of PTTH blunts age-dependent chronic inflammation, specifically in fly hepatocytes (oenocytes). Developmental transcriptomics reveal that NF-κB signaling activates during larva-to-adult transition, with PTTH inducing this signaling via ecdysone. Notably, time-restricted and oenocyte-specific silencing of Relish (an NF-κB homolog) at early 3rd instar larval stages significantly prolongs adult lifespan while delaying pupariation. Our study establishes an aging model that uncouples developmental time from growth rate, highlighting NF-κB signaling as a key developmental program in linking developmental time to adult lifespan.

Expression of innate immunity genes in human hematopoietic stem/progenitor cells - single cell RNA-seq analysis

Background

The complement system expressed intracellularly and known as complosome has been indicated as a trigger in the regulation of lymphocyte functioning. The expression of its genes was confirmed also in several types of human bone marrow-derived stem cells: mononuclear cells (MNCs), very small embryonic-like stem cells (VSELs), hematopoietic stem/progenitor cells (HSPCs), endothelial progenitors (EPCs) and mesenchymal stem cells (MSCs). In our previous studies, we demonstrated the expression of complosome proteins including C3, C5, C3aR, and cathepsin L in purified HSPCs. However, there is still a lack of results showing the expression of complosome system elements and other immunity-related proteins in human HSPCs at the level of single cell resolution.

Methods

We employed scRNA-seq to investigate comprehensively the expression of genes connected with immunity, in two populations of human HSPCs: CD34+Lin-CD45+ and CD133+Lin-CD45+, with the division to subpopulations. We focused on genes coding complosome elements, selected cytokines, and genes related to antigen presentation as well as related to immune regulation.

Results

We observed the differences in the expression of several genes e.g. C3AR1 and C5AR1 between two populations of HSPCs: CD34+LinCD45+ and CD133+Lin-CD45+ resulting from their heterogeneous nature. However, in both kinds of HSPCs, we observed similar cell subpopulations expressing genes (e.g. NLRP3 and IL-1β) at the same level, which suggests the presence of cells performing similar functions connected with the activation of inflammatory processes contributing to the body's defense against infections.

Discussion

To our best knowledge, it is the first time that expression of complosome elements was studied in HSPCs at the single cell resolution with the use of single cell sequencing. Thus, our data sheds new light on complosome as a novel regulator of hematopoiesis that involves intracrine activation of the C5a-C5aR-Nlrp3 inflammasome axis.

NOD1: a metabolic modulator

Nucleotide-binding oligomerization domain 1 (NOD1) is an intracellular pattern recognition receptor that detects injury signals and initiates inflammatory responses and host defense. Furthermore, NOD1 serves as a metabolic mediator by influencing the metabolism of various tissues, including adipose tissue, liver, cardiovascular tissue, pancreatic β cells, adrenal glands, and bones through diverse mechanisms. It has been discovered that activated NOD1 is associated with the pathological mechanisms of certain metabolic diseases. This review presents a comprehensive summary of the impact of NOD1 on tissue-specific metabolism.

Integrated Local and Systemic Communication Factors Regulate Nascent Hematopoietic Progenitor Escape During Developmental Hematopoiesis

Mammalian blood cells originate from specialized 'hemogenic' endothelial (HE) cells in major arteries. During the endothelial-to-hematopoietic transition (EHT), nascent hematopoietic stem cells (HSCs) bud from the arterial endothelial wall and enter circulation, destined to colonize the fetal liver before ultimately migrating to the bone marrow. Mechanisms and processes that facilitate EHT and the release of nascent HSCs are incompletely understood, but may involve signaling from neighboring vascular endothelial cells, stromal support cells, circulating pre-formed hematopoietic cells, and/or systemic factors secreted by distal organs. We used single cell RNA sequencing analysis from human embryonic cells to identify relevant signaling pathways that support nascent HSC release. In addition to intercellular and secreted signaling modalities that have been previously functionally validated to support EHT and/or developmental hematopoiesis in model systems, we identify several novel modalities with plausible mechanisms to support EHT and HSC release. Our findings paint a portrait of the complex inter-regulated signals from the local niche, circulating hematopoietic/inflammatory cells, and distal fetal liver that support hematopoiesis.

Tropomyosin 1 deficiency facilitates cell state transitions and enhances hemogenic endothelial cell specification during hematopoiesis

Tropomyosins coat actin filaments to impact actin-related signaling and cell morphogenesis. Genome-wide association studies have linked Tropomyosin 1 (TPM1) with human blood trait variation. TPM1 has been shown to regulate blood cell formation in vitro, but it remains unclear how or when TPM1 affects hematopoiesis. Using gene-edited induced pluripotent stem cell (iPSC) model systems, we found that TPM1 knockout augmented developmental cell state transitions and key signaling pathways, including tumor necrosis factor alpha (TNF-α) signaling, to promote hemogenic endothelial (HE) cell specification and hematopoietic progenitor cell (HPC) production. Single-cell analyses revealed decreased TPM1 expression during human HE specification, suggesting that TPM1 regulated in vivo hematopoiesis via similar mechanisms. Analyses of a TPM1 gene trap mouse model showed that TPM1 deficiency enhanced HE formation during embryogenesis, without increasing the number of hematopoietic stem cells. These findings illuminate novel effects of TPM1 on developmental hematopoiesis.

p65 signaling dynamics drive the developmental progression of hematopoietic stem and progenitor cells through cell cycle regulation

Most gene functions have been discovered through phenotypic observations under loss of function experiments that lack temporal control. However, cell signaling relies on limited transcriptional effectors, having to be re-used temporally and spatially within the organism. Despite that, the dynamic nature of signaling pathways have been overlooked due to the difficulty on their assessment, resulting in important bottlenecks. Here, we have utilized the rapid and synchronized developmental transitions occurring within the zebrafish embryo, in conjunction with custom NF-kB reporter embryos driving destabilized fluorophores that report signaling dynamics in real time. We reveal that NF-kB signaling works as a clock that controls the developmental progression of hematopoietic stem and progenitor cells (HSPCs) by two p65 activity waves that inhibit cell cycle. Temporal disruption of each wave results in contrasting phenotypic outcomes: loss of HSPCs due to impaired specification versus proliferative expansion and failure to delaminate from their niche. We also show functional conservation during human hematopoietic development using iPSC models. Our work identifies p65 as a previously unrecognized contributor to cell cycle regulation, revealing why and when pro-inflammatory signaling is required during HSPC development. It highlights the importance of considering and leveraging cell signaling as a temporally dynamic entity.

Blood and guts: how the intestinal microbiome shapes hematopoiesis and treatment of hematologic disease

ABSTRACT

Over the past 10 years, there has been a marked increase in recognition of the interplay between the intestinal microbiome and the hematopoietic system. Despite their apparent distance in the body, a large literature now supports the relevance of the normal intestinal microbiota to steady-state blood production, affecting both hematopoietic stem and progenitor cells as well as differentiated immune cells. Microbial metabolites enter the circulation where they can trigger cytokine signaling that influences hematopoiesis. Furthermore, the state of the microbiome is now recognized to affect outcomes from hematopoietic stem cell transplant, immunotherapy, and cellular therapies for hematologic malignancies. Here we review the mechanisms by which microbiotas influence hematopoiesis in development and adulthood as well as the avenues by which microbiotas are thought to impact stem cell transplant engraftment, graft-versus-host disease, and efficacy of cell and immunotherapies. We highlight areas of future research that may lead to reduced adverse effects of antibiotic use and improved outcomes for patients with hematologic conditions.

Inflammation in Development and Aging: Insights from the Zebrafish Model

Zebrafish are an emergent animal model to study human diseases due to their significant genetic similarity to humans, swift development, and genetic manipulability. Their utility extends to the exploration of the involvement of inflammation in host defense, immune responses, and tissue regeneration. Additionally, the zebrafish model system facilitates prompt screening of chemical compounds that affect inflammation. This study explored the diverse roles of inflammatory pathways in zebrafish development and aging. Serving as a crucial model, zebrafish provides insights into the intricate interplay of inflammation in both developmental and aging contexts. The evidence presented suggests that the same inflammatory signaling pathways often play instructive or beneficial roles during embryogenesis and are associated with malignancies in adults.