E. Coli LPS-induced calcium signaling regulates the expression of hypoxia-inducible factor 1alpha in periodontal ligament fibroblasts in a non-hypoxia-dependent manner.

Periodontitis, an inflammatory disease, can cause significant damage to the oral tissues which support the teeth. During the early development of periodontitis, periodontal ligament fibroblasts (PDLFs) undergo metabolic reprogramming regulated by hypoxia-inducible factor 1alpha (HIF-1alpha), which is strongly linked to the progression of inflammation. However, the precise mechanisms by which PDLFs regulate HIF-1alpha and its associated metabolic reprogramming during early inflammation remain unclear. This study illustrated that brief and low-dose exposure to Escherichia coli (E. coli) lipopolysaccharide (LPS) can serve as a non-hypoxic stimulus, effectively replicating early periodontal inflammatory reactions. This is evidenced by the upregulation of HIF-1alpha expression and the activation of HIF-1alpha-mediated crucial glycolytic enzymes, namely lactate dehydrogenase a, pyruvate kinase, and hexokinase 2, concomitant with an augmentation in the inflammatory response within PDLFs. We observed that the effects mentioned and their impact on macrophage polarization were notably attenuated when intracellular and extracellular stores of Ca(2+) were depleted using BAPTA-AM and Ca(2+)-free medium, respectively. Mechanistically, our findings demonstrated that the transcriptional process of HIF-1alpha is regulated by Ca(2+) during E. coli LPS stimulation, mediated through the signal transducer and activator of transcription 3 (STAT3) pathway. Additionally, we observed that the stabilization of intracellular HIF-1alpha proteins occurs via the endothelin (ET)-1-endothelin A receptor pathway, independent of hypoxia. Taken together, our research outcomes underscore the pivotal involvement of Ca(2+) in the onset of early periodontitis by modulating HIF-1alpha and glycolysis, thereby presenting novel avenues for early therapeutic interventions.