Biology subjects

Mbalaviele, G.

Publications and source records attributed to Mbalaviele, G..

13 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↗

bioRxiv2026

The osteoclast intracellular environment fosters bacterial growth during Staphylococcus aureus infection

Bone infections, which are predominantly caused by Staphylococcus (S.) aureus, can be difficult to treat and have high rates of chronicity and reoccurrence. We previously identified that osteoclasts, the cells that break down bone matrix, may contribute to disease progression by allowing S. aureus to replicate intracellularly. There we identified that this bacteriums ability to grow intracellularly is tied to the maturation of osteoclasts. In this study we addressed whether osteoclast differentiation supports intracellular growth by changing the host cells response to infection or by altering the host cell environment to better support S. aureus. Using dual species RNA-sequencing we analyzed host and bacterial transcripts of infected osteoclast and precursor bone marrow macrophage (BMM) cultures. Host transcript analysis suggests that infected osteoclasts are slow to upregulate bacterial response genes compared to BMMs. We also identify that the S. aureus transcriptional response is primarily determined by the host cell type, and that bacteria in osteoclasts upregulate carbon metabolism genes compared to those inside BMMs. By utilizing intracellular survival assays on S. aureus mutants deficient in carbon metabolism and related pathways we determine that S. aureus require glycolysis, acetyl-CoA synthesis, and aspartate biosynthesis for proliferation inside osteoclasts, although bacteria can survive without them. With differentiation, osteoclasts increase glutamine uptake, and this metabolite is required for S. aureus intracellular growth. Taken together, these findings suggest that osteoclasts support S. aureus intracellular growth by providing nutrients required to replicate in the context of a blunted antimicrobial response. IMPORTANCEInfectious osteomyelitis, bone infection, is frequently caused by the bacterium Staphylococcus aureus. Intracellular infection of cells that build bone, osteoblasts, and cells that resorb bone, osteoclasts, have been implicated in disease progression by providing a niche for immune evasion. While S. aureus in osteoblasts are largely quiescent, bacteria in osteoclasts proliferate and therefore may be a source of reemergent infection. Factors that promote this growth in osteoclasts are poorly characterized. In this study we find that osteoclasts have a diminished transcriptional response to infection and show that S. aureus acquire glucose and glutamine, which have high flux in osteoclasts, to support intracellular growth. We further observe that S. aureus in osteoclasts require aspartate synthesis to grow intracellularly. This work highlights the importance of host cellular metabolism for the intracellular fate of S. aureus as an added factor beyond the direct antimicrobial response.

microbiology↗

bioRxiv2025

Activation of the noncanonical inflammasome-GSDMD pathway triggers pyroptosis in bone marrow and promotes periosteal bone formation

Evidence indicating that inflammation is commonly associated with ectopic osteogenesis in certain autoimmune and infectious conditions challenges the dogma that inflammatory responses always suppress bone formation. In this study, we find that systemic administration of lipopolysaccharide (LPS) to mice causes not only inflammation in bone marrow, as expected, but also stimulates periosteal bone formation. This response can be reproduced in vitro as bone marrow supernatants from LPS-treated mice induce robust osteogenesis of skeletal stem cells (SSCs) compared to supernatants from PBS-treated counterparts. Periosteal bone accrual is partly dependent on periosteal leptin receptor-positive (LepR)+ SSCs but not bone marrow LepR+ or adiponectin (Adq)+ SSCs and correlates with pyroptosis within bone marrow. Consistent with the dependence of periosteal osteogenesis on pyroptosis, this response is slightly attenuated in Nlrp3-/- or caspase-1-/-mice but significantly inhibited in caspase-11-/-, caspase-1-/-;caspase-11-/-, or Gsdmd-/-mice. Our study reveals a novel role for pyroptosis in which lysed cells release intracellular contents that stimulate osteoprogenitors and promote osteogenic differentiation within the periosteal compartment.

cell biology↗

bioRxiv2025

Staphylococcus aureus inhibits the NLRP3 inflammasome in macrophages during the early phases of intracellular infection, but not the late phases

Staphylococcus aureus (S. aureus) is a highly virulent pathogen responsible for chronic infections such as osteomyelitis. Although its interaction with the host immune system has been widely studied, the specific role of inflammasomes in regulating the infection within macrophages remains unclear. We investigated this question using bone marrow-derived macrophages infected with S. aureus and observed a significant reduction in intracellular bacterial load beginning at 18 hours post-infection (hpi), which continued through 96 hpi. Notably, robust activation of the NLRP3 inflammasome--including inflammasome assembly, IL-1{beta} and GSDMD maturation, and pyroptosis--occurred only after 18 hpi. This led us to hypothesize that S. aureus suppresses inflammasome activation during early infection. Supporting this, infected BMDMs failed to respond robustly to LPS and nigericin up to 18 hpi, with partial recovery at later timepoints, suggesting that S. aureus initially inhibits NLRP3 signaling to persist within macrophages but is later counteracted by the host response.

immunology↗

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↗

bioRxiv2023

Tmem178 negatively regulates IL-1β production through inhibition of the NLRP3 inflammasome

ObjectiveInflammasomes modulate the release of bioactive IL-1{beta}. Excessive IL-1{beta} levels are detected in patients with systemic juvenile idiopathic arthritis (sJIA) and cytokine storm syndrome (CSS) with mutated and unmutated inflammasome components, raising questions on the mechanisms of IL-1{beta} regulation in these disorders. MethodsTo investigate how the NLRP3 inflammasome is modulated in sJIA, we focused on Tmem178, a negative regulator of calcium levels in macrophages, and measured IL-1{beta} and caspase-1 activation in wild-type (WT) and Tmem178-/- macrophages following calcium chelators, silencing of Stim1, a component of store-operated calcium entry (SOCE), or by expressing a Tmem178 mutant lacking Stim1 binding site. Mitochondrial function in both genotypes was assessed by measuring oxidative respiration, mitochondrial reactive oxygen species (mtROS), and mitochondrial damage. CSS development was analyzed in Perforin-/-/Tmem178-/- mice infected with LCMV in which inflammasome or IL-1 signaling was pharmacologically inhibited. Human TMEM178 and IL-1B transcripts were analyzed in a dataset of peripheral blood monocytes from healthy controls and active sJIA patients. ResultsTMEM178 levels are reduced in monocytes from sJIA patients while IL-1B show increased levels. Accordingly, Tmem178-/- macrophages produce elevated IL-1{beta} compared to WT cells. The elevated intracellular calcium levels following SOCE activation in Tmem178-/- macrophages induce mitochondrial damage, release mtROS, and ultimately, promote NLRP3 inflammasome activation. In vivo, inhibition of inflammasome or IL-1 neutralization prolongs Tmem178-/- mouse survival to LCMV-induced CSS. ConclusionDownregulation of Tmem178 levels may represent a new biomarker to identify sJIA/CSS patients that could benefit from receiving drugs targeting inflammasome signaling.

immunology↗

bioRxiv2023

NLRP1 inflammasome modulates senescence and senescence-associated secretory phenotype

Senescence is a cellular aging-related process triggered by different stresses and characterized by the secretion of various inflammatory factors referred to as the senescence-associated secretory phenotype (SASP). Here, we present evidence that the inflammasome sensor, NLRP1, is a key mediator of senescence induced by irradiation both in vitro and in vivo. The NLRP1 inflammasome promotes senescence by regulating the expression of p16, p21, p53, and SASP in Gasdermin D (GSDMD)-dependent manner as these responses are reduced in conditions of NLRP1 insufficiency or GSDMD inhibition. Mechanistically, the NLRP1 inflammasome is activated downstream of the cytosolic DNA sensor cGMP-AMP (cGAMP) synthase (cGAS) in response to genomic damage. These findings provide a rationale for inhibiting the NLRP1 inflammasome-GSDMD axis to treat senescence-driven disorders.

immunology↗

bioRxiv2022

NEK7 activates the NLRP1 Inflammasome

Inflammasomes including those assembled by NLRP1 and NLRP3 regulate the innate immune system by inducing interleukin (IL)-1{beta} and IL-18 maturation. Inflammasomes are functionally regulated by post-translational modifications such as phosphorylation. The current paradigm posits that NEK7 is the essential and seletive activator of NLRP3; whether this kinase interacts with NLRP3 structurally-related member, NLRP1, has never been explored. Here, we find that NEK7 binds to NLRP1 and promotes its activation independently of NLRP3. IL-1{beta} maturation induced by NLRP1 or NLRP3 inflammasome activators, but not those of the NLRC4 or AIM2 inflammasome is impared in Nek7 deficient cells. This discovery expands the spectrum of NEK7 actions in the regulation of inflammasome pathways.

immunology↗

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↗

bioRxiv2020

Inhibition of the NLRP3 inflammasome prevents ovarian aging

Inflammation is a hallmark of many processes during aging and reproductive physiology, negatively affecting female fertility. The goal of this study was to evaluate the role of the NLRP3 inflammasome in ovarian aging and female fertility. Age-dependent increased expression of NLRP3 in the ovary was observed in female WT mice during reproductive aging. High expression of NLRP3, caspase 1 and IL-1{beta} was also observed in granulosa cells from patients with primary ovarian insufficiency. Ablation of the NLRP3 inflammasome improved the survival and pregnancy rates in mice, increased hormonal levels of AMH, a biochemical marker of ovarian reserve, and autophagy rates in ovarian tissue. Deficiency of the NLRP3 inflammasome also reduced serum FSH and estradiol levels. Consistent with these results, pharmacological inhibition of NLRP3 using a direct NLRP3 inhibitor, MCC950, improved fertility in female mice to levels comparable to those of Nlrp3-/- mice. These results suggest that the NLRP3 inflammasome is implicated in the age-dependent loss of female fertility and position this inflammasome as a potential new therapeutic target for the treatment of infertility.

immunology↗