Biology subjects

Abu-Amer, Y.

Publications and source records attributed to Abu-Amer, Y..

7 recordsLinked to original sources

bioRxiv2026

Pyroptotic cell-derived factors promote osteoclast differentiation

The NLRP3 D301N substitution, the murine ortholog of the human D303N variant, causes NLRP3 constitutive activation (NLRP3CA) and inflammasome assembly. Here, we show that priming signals induced by lipopolysaccharide (LPS) are sufficient to trigger GSDMD-dependent pyroptosis in NLRP3CA-expressing bone marrow-derived macrophages (BMDMs), but not in wild-type (NLRP3WT) cells. NLRP3CA mice exhibit elevated IL-1{beta} secretion and LDH release in bone marrow supernatants under both basal and LPS-challenged conditions. Other cytokines (e.g., TNF-) increased comparably between genotypes, indicating that NLRP3CA specifically amplifies inflammasome-dependent responses. Conditioned medium (CM) from LPS-treated NLRP3CA BMDMs significantly enhanced osteoclast (OC) differentiation in vivo and in vitro compared to NLRP3WT CM, as did bone marrow supernatants from NLRP3CA mice. This osteoclastogenic activity was largely independent of IL-1{beta}, as demonstrated by experiments using IL-1{beta}-deficient NLRP3CA BMDMs, IL-1{beta}-neutralizing antibodies, and genetic deletion of the IL-1 receptor. The osteoclastogenic factors were primarily soluble proteins, as heat inactivation and proteinase K digestion markedly reduced OC formation. Extracellular vesicles (EVs) from NLRP3CA CM modestly promoted OC differentiation, but EV-depleted supernatants retained full activity, indicating that the primary mediators are soluble proteins not carried within EVs. Together, these findings establish NLRP3CA as a well-controlled model for studying pyroptosis and demonstrate that pyroptotic cells release soluble proteins that drive osteoclastogenesis independently of IL-1{beta}.

cell biology↗

bioRxiv2025

NLRP3 inflammasome is regulated in osteoclasts through a Tmem178-dependent mechanism that restricts calcium influx

Osteoclasts (OCs) differentiate from macrophages in response to RANKL. Here, we investigated the role of the NLRP3 inflammasome in mouse macrophages, with or without exposure to RANKL. Unexpectedly, we found that NLRP3 expression gradually declined during osteoclastogenesis but could be restored with LPS treatment. LPS and nigericin robustly activated this inflammasome in macrophages, as expected, but not in OCs. Mechanistically, we identified Tmem178, a protein that restrains Ca2+ release from the endoplasmic reticulum (ER) and highly expressed in OCs, as an inhibitor of this inflammasome. Notably, NLRP3 inflammasome activation was robust in OCs lacking Tmem178 or wild-type (WT) OCs exposed to high calcium concentrations. In vivo studies demonstrated that under the conditions where OCs efficiently release Ca2+ from bone, inflammasome formation was enhanced. Furthermore, deletion of Nlrp3 rescued osteopenia in Tmem178-/- mice. Thus, we found that Tmem178 uniquely restricts Ca2+ release from ER in OCs, thereby suppressing NLRP3 inflammasome activation. One Sentence SummaryThe NLRP3 inflammasome is silenced in the OC lineage by Tmem178 to prevent pathological bone loss.

immunology↗

bioRxiv2023

Chemotherapy activates inflammasomes to cause inflammation-associated bone loss

Chemotherapy is a widely used treatment for a variety of solid and hematological malignancies. Despite its success in improving the survival rate of cancer patients, chemotherapy causes significant toxicity to multiple organs, including the skeleton, but the underlying mechanisms have yet to be elucidated. Using tumor-free mouse models, which are commonly used to assess direct off-target effects of anti-neoplastic therapies, we found that doxorubicin caused massive bone loss in wild-type mice, a phenotype associated with increased number of osteoclasts, leukopenia, elevated serum levels of danger-associated molecular patterns (DAMPs; e.g., cell-free DNA and ATP) and cytokines (e.g., IL-1{beta} and IL-18). Accordingly, doxorubicin activated the absent in melanoma (AIM2) and NLR family pyrin domain containing 3 (NLRP3) inflammasomes in macrophages and neutrophils, causing inflammatory cell death pyroptosis and NETosis, which correlated with its leukopenic effects. Moreover, the effects of this chemotherapeutic agent on cytokine secretion, cell demise, and bone loss were attenuated to various extent in conditions of AIM2 and/or NLRP3 insufficiency. Thus, we found that inflammasomes are key players in bone loss caused by doxorubicin, a finding that may inspire the development of a tailored adjuvant therapy that preserves the quality of this tissue in patients treated with this class of drugs.

cell biology↗

bioRxiv2022

Tenotomy-induced muscle atrophy is sex-specific and independent of NFκB

The nuclear factor-{kappa}B (NF{kappa}B) pathway is a major thoroughfare for skeletal muscle atrophy and is driven by diverse stimuli. Targeted inhibition of NF{kappa}B through its canonical mediator IKK{beta} effectively mitigates loss of muscle mass across many conditions, from denervation to unloading to cancer. In this study, we used gain- and loss-of-function mouse models to examine the role of NF{kappa}B in muscle atrophy following rotator cuff tenotomy - a model of chronic rotator cuff tear. IKK{beta} was knocked down or constitutively activated in muscle-specific inducible transgenic mice to elicit a 2-fold gain or loss of NF{kappa}B signaling. Surprisingly, neither knockdown of IKK{beta} nor overexpression of caIKK{beta} significantly altered the loss of muscle mass following tenotomy. This finding was consistent across measures of architectural adaptation (fiber cross-sectional area, fiber length, fiber number), tissue pathology (fibrosis and fatty infiltration) and intracellular signaling (ubiquitin-proteasome, autophagy). Intriguingly, late-stage tenotomy-induced atrophy was exacerbated in male mice compared to female mice. This sex specificity was driven by ongoing decreases in fiber cross-sectional area, which paralleled the accumulation of large autophagic vesicles in male, but not female muscle. These findings suggest that tenotomy-induced atrophy is not dependent on NF{kappa}B and instead may be regulated by autophagy in a sex-specific manner.

physiology↗

bioRxiv2022

Glutamine metabolism modulates chondrocyte inflammatory response

Osteoarthritis is the most common joint disease in the world with significant societal consequences, but lacks effective disease modifying interventions. The pathophysiology consists of a prominent inflammatory component that can be targeted to prevent cartilage degradation and structural defects. Intracellular metabolism has emerged as a culprit of the inflammatory response in chondrocytes, with both processes co-regulating each other. The role of glutamine metabolism in chondrocytes, especially in the context of inflammation, lacks a thorough understanding and is the focus of this work. We display that chondrocytes utilize glutamine for energy production and anabolic processes. Furthermore, we show that glutamine deprivation itself causes metabolic reprogramming and decreases the inflammatory response of chondrocytes through inhibition of NF-{kappa}B activity. Finally, we display that glutamine deprivation promotes autophagy and that ammonia is an inhibitor of autophagy. Overall, we identify a relationship between glutamine metabolism and inflammatory signaling and display the need for increased study of chondrocyte metabolic systems.

biochemistry↗

bioRxiv2021

Fracture healing is delayed in the absence of gasdermin signaling

Amino-terminal fragments from proteolytically cleaved gasdermins (GSDMs) form plasma membrane pores that enable the secretion of interleukin-1{beta} (IL-1{beta}) and IL-18. Excessive GSDM- mediated pore formation can compromise the integrity of the plasma membrane thereby causing the lytic inflammatory cell death, pyroptosis. We found that GSDMD and GSDME were the only GSDMs that were readily expressed in bone microenvironment. Therefore, we tested the hypothesis that GSDMD and GSDME are implicated in fracture healing owing to their role in the obligatory inflammatory response following injury. We found that bone callus volume and biomechanical properties of injured bones were significantly reduced in mice lacking either GSDM compared with wild-type (WT) mice, indicating that fracture healing was compromised in mutant mice. However, compound loss of GSDMD and GSDME did not exacerbate the outcomes, suggesting shared actions of both GSDMs in fracture healing. Mechanistically, bone injury induced IL-1{beta} and IL-18 secretion in vivo, a response that was mimicked in vitro by bone debris and ATP, which function as inflammatory danger signals. Importantly, the secretion of these cytokines was attenuated in conditions of GSDMD deficiency. Finally, deletion of IL-1 receptor reproduced the phenotype of Gsdmd or Gsdme deficient mice, implying that inflammatory responses induced by the GSDM-IL-1 axis promote bone healing after fracture.

immunology↗

bioRxiv2021

Activation of GSDME compensates for GSDMD deficiency in a mouse model of NLRP3 inflammasomopathy

The D301N NLRP3 mutation in mice (D303N in humans) causes severe multi-organ damage and early death driven by the constitutively activated NLRP3 (NLRP3ca) inflammasome. Triggered inflammasomes activate caspase-1 to process IL-1 family cytokines and gasdermin D (GSDMD), generating N-terminal fragments, which oligomerize within the plasma membrane to form pores, which cause inflammatory cell death (pyroptosis) and through which IL-1{beta} and IL-18 are secreted. GSDMD activation is central to disease symptoms since spontaneous inflammation in Nlrp3ca;Gsdmd-/- mice is negligible. Unexpectedly, when Nlrp3ca;Gsdmd-/- mice were challenged with LPS or TNF-, they secreted high amounts of IL-1{beta} and IL-18, suggesting an alternative GSDMD-independent inflammatory pathway. Here we show that GSDMD deficient macrophages subjected to inflammatory stimuli activate caspase-8, -3 and GSDME-dependent cytokine release and pyroptosis. Caspase-8, -3 and GSDME also activated pyroptosis when NLRP3 was stimulated in caspase-1 deficient macrophages. Thus, a salvage caspase-8, -3-GSDME inflammatory pathway is activated following NLRP3 activation when the canonical NLRP3-caspase-1-GSDMD is blocked. Surprisingly, the active metabolite of the GSDMD-inhibitor disulfiram, inhibited not only GSDMD but also GSDME-mediated inflammation in vitro and suppressed severe inflammatory disease symptoms in Nlrp3ca mice, a model for severe neonatal multisystem inflammatory disease. Although disulfiram did not directly inhibit GSDME, it suppressed inflammasome activation in GSDMD-deficient cells. Thus, the combination of inflammatory signals and NLRP3ca overwhelmed the protection provided by GSDMD deficiency, rewiring signaling cascades through caspase-8, -3 and GSDME to propagate inflammation. This functional redundancy suggests that concomitant inhibition of GSDMD and GSDME may be necessary to suppress disease in inflammasomopathy patients.

immunology↗