Dataset Information

Deletion of the NF-?B subunit p65/RelA in the hematopoietic compartment leads to defects in hematopoietic stem cell function.

ABSTRACT: Hematopoiesis is a tightly regulated process resulting in the production of blood cells. Self-renewal and differentiation of hematopoietic stem cells (HSCs) are key processes in hematopoietic development. Disruption of these steps can lead to altered cell distribution and disease. To investigate the role of the nuclear factor-?B subunit RelA/p65 in the regulation of HSCs in vivo, we generated mice lacking RelA/p65 in the hematopoietic compartment. Using this model system, we show that loss of p65 severely impairs HSC function and occurs in conjunction with increased hematopoietic stem and progenitor cell cycling, extramedullary hematopoiesis, and differentiation defects. Gene array studies of phenotypic HSCs indicate the up-regulation of genes normally expressed in lineage restricted cells, as well as the down-regulation of genes involved in HSC maintenance and homeostasis. We hypothesize that changes in gene expression in p65-deficient cells lead to decreased self-renewal and differentiation efficiency of hematopoietic stem and progenitor cells. These studies demonstrate that p65 is an important regulator of hematopoiesis through the transcription of genes involved in HSC fate.

SUBMITTER: Stein SJ

PROVIDER: S-EPMC3689248 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature

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Deletion of the NF-κB subunit p65/RelA in the hematopoietic compartment leads to defects in hematopoietic stem cell function.

Stein Sarah J SJ Baldwin Albert S AS

Blood 20130513 25

Hematopoiesis is a tightly regulated process resulting in the production of blood cells. Self-renewal and differentiation of hematopoietic stem cells (HSCs) are key processes in hematopoietic development. Disruption of these steps can lead to altered cell distribution and disease. To investigate the role of the nuclear factor-κB subunit RelA/p65 in the regulation of HSCs in vivo, we generated mice lacking RelA/p65 in the hematopoietic compartment. Using this model system, we show that loss of p6 ...[more]

PMID: 23670180

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Project description:The NF-κB signaling pathway is central to the innate and adaptive immune responses. Upon their detection of pathogen-associated molecular patterns, Toll-like receptors on the cell surface initiate signal transduction and activate the NF-κB pathway, leading to the production of a wide array of inflammatory cytokines, in attempt to eradicate the invaders. As a countermeasure, pathogens have evolved ways to subvert and manipulate this system to their advantage. Enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC) are closely related bacteria responsible for major food-borne diseases worldwide. Via a needle-like protein complex called the type three secretion system (T3SS), these pathogens deliver virulence factors directly to host cells and modify cellular functions, including by suppressing the inflammatory response. Using gain- and loss-of-function screenings, we identified two bacterial effectors, NleC and NleE, that down-regulate the NF-κB signal upon being injected into a host cell via the T3SS. A recent report showed that NleE inhibits NF-κB activation, although an NleE-deficient pathogen was still immune-suppressive, indicating that other anti-inflammatory effectors are involved. In agreement, our present results showed that NleC was also required to inhibit inflammation. We found that NleC is a zinc protease that disrupts NF-κB activation by the direct cleavage of NF-κB's p65 subunit in the cytoplasm, thereby decreasing the available p65 and reducing the total nuclear entry of active p65. More importantly, we showed that a mutant EPEC/EHEC lacking both NleC and NleE (ΔnleC ΔnleE) caused greater inflammatory response than bacteria carrying ΔnleC or ΔnleE alone. This effect was similar to that of a T3SS-defective mutant. In conclusion, we found that NleC is an anti-inflammatory bacterial zinc protease, and that the cooperative function of NleE and NleC disrupts the NF-κB pathway and accounts for most of the immune suppression caused by EHEC/EPEC.

Project description:Heritable disorders that feature high bone mass (HBM) are rare. The etiology is typically a mutation(s) within a gene that regulates the differentiation and function of osteoblasts (OBs) or osteoclasts (OCs). Nevertheless, the molecular basis is unknown for approximately one-fifth of such entities. NF-?B signaling is a key regulator of bone remodeling and acts by enhancing OC survival while impairing OB maturation and function. The NF-?B transcription complex comprises five subunits. In mice, deletion of the p50 and p52 subunits together causes osteopetrosis (OPT). In humans, however, mutations within the genes that encode the NF-?B complex, including the Rela/p65 subunit, have not been reported. We describe a neonate who died suddenly and unexpectedly and was found at postmortem to have HBM documented radiographically and by skeletal histopathology. Serum was not available for study. Radiographic changes resembled malignant OPT, but histopathological investigation showed morphologically normal OCs and evidence of intact bone resorption excluding OPT. Furthermore, mutation analysis was negative for eight genes associated with OPT or HBM. Instead, accelerated bone formation appeared to account for the HBM. Subsequently, trio-based whole exome sequencing revealed a heterozygous de novo missense mutation (c.1534_1535delinsAG, p.Asp512Ser) in exon 11 of RELA encoding Rela/p65. The mutation was then verified using bidirectional Sanger sequencing. Lipopolysaccharide stimulation of patient fibroblasts elicited impaired NF-?B responses compared with healthy control fibroblasts. Five unrelated patients with unexplained HBM did not show a RELA defect. Ours is apparently the first report of a mutation within the NF-?B complex in humans. The missense change is associated with neonatal osteosclerosis from in utero increased OB function rather than failed OC action. These findings demonstrate the importance of the Rela/p65 subunit within the NF-?B pathway for human skeletal homeostasis and represent a new genetic cause of HBM.

Dataset Information

Deletion of the NF-?B subunit p65/RelA in the hematopoietic compartment leads to defects in hematopoietic stem cell function.

Publications

Deletion of the NF-κB subunit p65/RelA in the hematopoietic compartment leads to defects in hematopoietic stem cell function.

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