Connexin 43 and Pannexin 1 hemichannels as endogenous regulators of innate immunity in sepsis

Abstract

Sepsis is a life-threatening organ dysfunction resulting from a dysregulated host response to infections that is initiated by the body's innate immune system. Nearly a decade ago, we discovered that bacterial lipopolysaccharide (LPS) and serum amyloid A (SAA) upregulated Connexin 43 (Cx43) and Pannexin 1 (Panx1) hemichannels in macrophages. When overexpressed, these hemichannels contribute to sepsis pathogenesis by promoting ATP efflux, which intensifies the double-stranded RNA-activated protein kinase R (PKR)-dependent inflammasome activation, pyroptosis, and the release of pathogenic damage-associated molecular pattern (DAMP) molecules, such as HMGB1. Mimetic peptides targeting specific regions of Cx43 and Panx1 can distinctly modulate hemichannel activity in vitro, and diversely impact sepsis-induced lethality in vivo. Along with extensive supporting evidence from others, we now propose that hemichannel molecules play critical roles as endogenous regulators of innate immunity in sepsis.

Keywords: ATP; Connexin 43; HMGB1; Pannexin 1; hemichannel; inflammasome; innate immune cells; mimetic peptide.

Figure 1

Proposed roles of Cx43 and Panx1 hemichannels in regulating ATP release and inflammasome activation. Prolonged exposure to crude LPS or SAA induced upregulation of Cx43 and Panx1 hemichannels, potentially contributing to extracellular ATP efflux, P2X7R-mediated PKR phosphorylation, pyroptosis, and the release of DAMPs such as HMGB1. Concurrently, PKR activation led to increased expression of inducible nitric oxide synthase (iNOS) and parallel production of nitric oxide (NO) in macrophage cultures.

Figure 2

Amino acid sequence and structural domains of human Cx43 and Panx1. (A) highlights various mimetic peptides that correspond to specific regions within the extracellular or cytoplasmic loops of Cx43 or Panx1 protein. (B) presents the three-dimensional structures of Cx43 and Panx1 hemichannels, including the Panx1 variant lacking the C-terminal tail (ΔPanx1).