Nontypeable Haemophilus Influenzae Infection Upregulates the NLRP3 Inflammasome and Leads to Caspase-1-Dependent Secretion of Interleukin-1β — A Possible Pathway of Exacerbations in COPD

Abstract

Rationale Nontypeable Haemophilus influenzae (NTHi) is the most common cause for bacterial exacerbations in chronic obstructive pulmonary disease (COPD). Recent investigations suggest the participation of the inflammasome in the pathomechanism of airway inflammation. The inflammasome is a cytosolic protein complex important for early inflammatory responses, by processing Interleukin-1β (IL-1β) to its active form.ObjectivesSince inflammasome activation has been described for a variety of inflammatory diseases, we investigated whether this pathway plays a role in NTHi infection of the airways.MethodsA murine macrophage cell line (RAW 264.7), human alveolar macrophages and human lung tissue (HLT) were stimulated with viable or non-viable NTHi and/or nigericin, a potassium ionophore. Secreted cytokines were measured with ELISA and participating proteins detected via Western Blot or immunohistochemistry.Measurements and Main ResultsWestern Blot analysis of cells and immunohistochemistry of lung tissue detected the inflammasome key components NLRP3 and caspase-1 after stimulation, leading to a significant induction of IL-1β expression (RAW: control at the lower detection limit vs. NTHi 505±111pg/ml, p<0.01). Inhibition of caspase-1 in human lung tissue led to a significant reduction of IL-1β and IL-18 levels (IL-1β: NTHi 24 h 17423±3198pg/ml vs. NTHi+Z-YVAD-FMK 6961±1751pg/ml, p<0.01).ConclusionOur data demonstrate the upregulation of the NRLP3-inflammasome during NTHi-induced inflammation in respiratory cells and tissues. Our findings concerning caspase-1 dependent IL-1β release suggest a role for the inflammasome in respiratory tract infections with NTHi which may be relevant for the pathogenesis of bacterial exacerbations in COPD.

Ndfip1 Regulates Itch Ligase Activity and Airway Inflammation via UbcH7

“…Because myeloid-derived proinflammatory cytokines play crucial roles in NTHi-induced lung inflammation and chronic obstructive pulmonary disease (18,(25)(26)(27)(28), we used FACS to sort CD11b + cells from the lung tissues of WT, Itch 2/2 , and Ndfip1 2/2 mice. Expression of proinflammatory cytokines was analyzed by real-time PCR.…”

Investigating the Role of Nucleotide-Binding Oligomerization Domain–Like Receptors in Bacterial Lung Infection

“…NLRP3 has been principally studied in human and murine macrophages; however, NLRP3 inflammasome constituents are also expressed in human and murine airway epithelial cells on bacterial challenge (25). The defining feature of NLRP3 is the N-terminal PYD that homotypically binds PYD of ASC.…”

“…The two-signal process may act as a cellular safeguard against hyperactivation of the NLRP3 inflammasome. Although other inflammasomes may not depend on TLR signaling for synthesis of their constituent molecules, it should be noted that TLR signaling does contribute to increased cytosolic expression of pro-IL-1b, and production of mature IL-1b by other inflammasomes may be impacted by TLR activation (25).…”

“…Nontypeable H. influenzae (NTHi) is the most important bacterial species responsible for acute exacerbations of COPD (25). Stimulation with NTHi induced NLRP3 inflammasome upregulation in human and murine macrophages and human bronchial epithelial cells (25).…”

“…Stimulation with NTHi induced NLRP3 inflammasome upregulation in human and murine macrophages and human bronchial epithelial cells (25). Moreover, stimulation with NTHi led to caspase-1 induction and production of IL-1b and IL-18 in human lung tissue, indicating that NLRP3 may be an active player in acute inflammation during bacterial infections in patients with COPD (25).…”