Neuronal self-injury mediated by IL-1β and MMP-9 in a cerebral palsy model of severe neonatal encephalopathy induced by immune activation plus hypoxia-ischemia

J Neuroinflammation. 2015 May 30;12:111. doi: 10.1186/s12974-015-0330-8.


Background: Inflammation due to remote pathogen exposure combined to hypoxia/ischemia (HI) is one of the most common causes of neonatal encephalopathy affecting at-term or near-term human newborn, which will consequently develop cerebral palsy. Within term-equivalent rat brains exposed to systemic lipopolysaccharide (LPS) plus HI, it was previously showed that neurons produce IL-1β earlier than do glial cells, and that blocking IL-1 was neuroprotective. To further define the mechanisms whereby IL-1 exerts its neurotoxic effect, we hypothesize that IL-1β plays a pivotal role in a direct and/or indirect mechanistic loop of neuronal self-injury through matrix metalloproteinase (MMP)-9.

Methods: An established preclinical rat model of LPS+HI-induced neonatal encephalopathy was used. In situ hybridization, ELISA, and immunolabeling techniques were employed. Selective blocking compounds allowed addressing the respective roles of IL-1 and MMP-9.

Results: In LPS+HI-exposed forebrains, neuronal IL-1β was first detected in infarcted neocortical and striatal areas and later in glial cells of the adjacent white matter. Neuronal IL-1β played a key role: (i) in the early post-HI exacerbation of neuroinflammation and (ii) in generating both core and penumbral infarcted cerebral areas. Systemically administered IL-1 receptor antagonist (IL-1Ra) reached the brain and bound to the neocortical and deep gray neuronal membranes. Then, IL-1Ra down-regulated IL-1β mRNA and MMP-9 neuronal synthesis. Immediately post-HI, neuronal IL-1β up-regulated cytokine-induced neutrophil chemoattractant (CINC-1), monocyte chemoattractant protein-1 (MCP-1), and inducible nitric oxide synthase. MMP-9 would disrupt the blood-brain barrier, which, combined to CINC-1 up-regulation, would play a role in polymorphonuclear cell (PMN) infiltration into the LPS+HI-exposed brain. IL-1β blockade prevented PMN infiltration and oriented the phenotype of macrophagic/microglial cells towards anti-inflammatory and neurotrophic M2 profile. IL-1β increased the expression of activated caspase-3 and of receptor-interacting-protein (RIP)-3 within infarcted forebrain area. Such apoptotic and necroptotic pathway activations were prevented by IL-1Ra, as well as ensuing cerebral palsy-like brain damage and motor impairment.

Conclusions: This work uncovered a new paradigm of neuronal self-injury orchestrated by neuronal synthesis of IL-1β and MMP-9. In addition, it reinforced the translational neuroprotective potential of IL-1 blockers to alleviate human perinatal brain injuries.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Age Factors
  • Animals
  • Animals, Newborn
  • Brain Diseases* / etiology
  • Brain Diseases* / metabolism
  • Brain Diseases* / pathology
  • Caspase 3 / metabolism
  • Cerebral Palsy / chemically induced
  • Cerebral Palsy / complications*
  • Cerebral Palsy / immunology
  • Disease Models, Animal
  • Glial Fibrillary Acidic Protein / metabolism
  • Hypoxia-Ischemia, Brain / complications*
  • Hypoxia-Ischemia, Brain / pathology
  • Interleukin 1 Receptor Antagonist Protein / genetics
  • Interleukin 1 Receptor Antagonist Protein / metabolism
  • Interleukin-1beta / genetics
  • Interleukin-1beta / metabolism*
  • Lipopolysaccharides / toxicity
  • Matrix Metalloproteinase 9 / genetics
  • Matrix Metalloproteinase 9 / metabolism*
  • Motor Activity / drug effects
  • Neurons / metabolism*
  • Neurons / pathology
  • Rats
  • Rats, Inbred Lew
  • Receptor-Interacting Protein Serine-Threonine Kinases / metabolism
  • Stereotyped Behavior / drug effects


  • Glial Fibrillary Acidic Protein
  • Interleukin 1 Receptor Antagonist Protein
  • Interleukin-1beta
  • Lipopolysaccharides
  • Receptor-Interacting Protein Serine-Threonine Kinases
  • receptor-interacting protein 3, rat
  • Caspase 3
  • Matrix Metalloproteinase 9