Transient Receptor Potential Vanilloid-1 Channels Facilitate Axonal Degeneration of Corneal Sensory Nerves in Dry Eye.

Corneal nerve impairment contributes significantly to dry eye disease (DED) symptoms and is thought to be secondary to corneal epithelial damage. Transient receptor potential vanilloid-1 (TRPV1) channels abound in corneal nerve fibers and respond to inflammation-derived ligands, which increase in DED. TRPV1 overactivation promotes axonal degeneration in vitro, but whether it participates in DED-associated corneal nerve dysfunction is unknown. To explore this, DED was surgically induced in wild-type and TRPV1-knockout mice, which developed comparable corneal epithelial damage and reduced tear secretion. However, corneal mechanosensitivity decreased progressively only in wild-type DED mice. Sensitivity to capsaicin (TRPV1 agonist) increased in wild-type DED mice, and consistently, only this strain displayed DED-induced pain signs. Wild-type DED mice exhibited nerve degeneration throughout the corneal epithelium, whereas TRPV1-knockout DED mice only developed a reduction in the most superficial nerve endings that failed to propagate to the deeper subbasal corneal nerves. Pharmacologic TRPV1 blockade reproduced these findings in wild-type DED mice, whereas CD4+ T cells from both strains were equally pathogenic when transferred, ruling out a T-cell-mediated effect of TRPV1 deficiency. These data show that ocular desiccation triggers superficial corneal nerve damage in DED, but proximal propagation of axonal degeneration requires TRPV1 expression. Local inflammation sensitized TRPV1 channels, which increased ocular pain. Thus, ocular TRPV1 overactivation drives DED-associated corneal nerve impairment.

Regulation of human neutrophil IL-1ß secretion induced by Escherichia coli O157:H7 responsible for hemolytic uremic syndrome.

Shiga-toxin producing Escherichia coli (STEC) infections can cause from bloody diarrhea to Hemolytic Uremic Syndrome. The STEC intestinal infection triggers an inflammatory response that can facilitate the development of a systemic disease. We report here that neutrophils might contribute to this inflammatory response by secreting Interleukin 1 beta (IL-1ß). STEC stimulated neutrophils to release elevated levels of IL-1ß through a mechanism that involved the activation of caspase-1 driven by the NLRP3-inflammasome and neutrophil serine proteases (NSPs). Noteworthy, IL-1ß secretion was higher at lower multiplicities of infection. This secretory profile modulated by the bacteria:neutrophil ratio, was the consequence of a regulatory mechanism that reduced IL-1ß secretion the higher were the levels of activation of both caspase-1 and NSPs, and the production of NADPH oxidase-dependent reactive oxygen species. Finally, we also found that inhibition of NSPs significantly reduced STEC-triggered IL-1ß secretion without modulating the ability of neutrophils to kill the bacteria, suggesting NSPs might represent pharmacological targets to be evaluated to limit the STEC-induced intestinal inflammation.

The interplay between serine proteases and caspase-1 regulates the autophagy-mediated secretion of Interleukin-1 beta in human neutrophils.

Neutrophils play major roles against bacteria and fungi infections not only due to their microbicide properties but also because they release mediators like Interleukin-1 beta (IL-1ß) that contribute to orchestrate the inflammatory response. This cytokine is a leaderless protein synthesized in the cytoplasm as a precursor (pro-IL-1ß) that is proteolytically processed to its active isoform and released from human neutrophils by secretory autophagy. In most myeloid cells, pro-IL-1ß is processed by caspase-1 upon inflammasome activation. Here we employed neutrophils from both healthy donors and patients with a gain-of-function (GOF) NLRP3-mutation to dissect IL-1ß processing in these cells. We found that although caspase-1 is required for IL-1ß secretion, it undergoes rapid inactivation, and instead, neutrophil serine proteases play a key role in pro-IL-1ß processing. Our findings bring to light distinctive features of the regulation of caspase-1 activity in human neutrophils and reveal new molecular mechanisms that control human neutrophil IL-1ß secretion.