Regulation of Toll-like receptor 1 and -2 in neonatal mice brains after hypoxia-ischemia

Abstract

BackgroundHypoxic-ischemic (HI) brain injury remains a major problem in newborns, resulting in increased risk of neurological disorders. Neonatal HI triggers a broad inflammatory reaction in the brain, including activation of the innate immune system. Toll-like receptors (TLRs), which are key components of the innate immune system, are believed to play a role in adult cerebral ischemic injury. The expression of TLRs in the neonatal brain and their regulation after HI is unknown.MethodsWild type C57BL/6, TLR 1 knockout (KO) and TLR 2 KO mice were subjected to HI at postnatal day 9 and sacrificed 30 min, 6 h, 24 h or 5 days after HI. TLR mRNA expression was determined by RT-qPCR and protein and cell type localisation by immunohistochemistry (IHC). To evaluate brain injury, infarct volume was measured in the injured hemisphere.ResultsmRNA expression was detected for all investigated TLRs (TLR1-9), both in normal and HI exposed brains. After HI, TLR-1 was down-regulated at 30 min and up-regulated at 6 h and 24 h. TLR-2 was up-regulated at 6 h and 24 h, and TLR-7 at 24 h. Both TLR-5 and TLR-8 were down-regulated at 24 h and 30 min respectively. IHC showed an increase of TLR-1 in neurons in the ipsilateral hemisphere after HI. TLR-2 was constitutively expressed in astrocytes and in a population of neurons in the paraventricular nucleus in the hypothalamus. No changes in expression were detected following HI. Following HI, TLR-2 KO mice, but not TLR-1 KO, showed a decreased infarct volume compared to wild type (p = 0.0051).ConclusionsThis study demonstrates that TLRs are regulated after HI in the neonatal brain. TLR-1 protein was up-regulated in injured areas of the brain but TLR-1 KO animals were not protected from HI. In contrast, TLR-2 was constitutively expressed in the brain and TLR-2 deficiency reduced HI injury. These data suggest that TLR-2, but not TLR-1, plays a role in neonatal HI brain injury.

TLR1 expression in mouse brain was increased in a KA-induced seizure model

“…Previous studies have demonstrated that TLR1 and TLR2 cooperate in the recognition of lipopeptides [13]. In addition, both TLR1 and TLR2 are upregulated during hypoxic-ischemic brain injury suggesting a synergistic role between TLR1 and TLR2 in this process [14]. These results also suggest that TLR1 may also play an important role in epilepsy.…”

Staphylococcus epidermidisBacteremia Induces Brain Injury in Neonatal Mice via Toll-like Receptor 2-Dependent and -Independent Pathways

“…Indeed, in our current study TLR2−/− neonatal mice demonstrated delayed clearance of S. epidermidis from the bloodstream, spleen, and liver. In addition to its important roles in host defense in clearing bacteria, TLR2 may mediate some forms of inflammatory brain injury [42], including middle cerebral artery occlusion [43] and neonatal hypoxia-ischemiainduced brain injury [44]. Indeed, consistent with the known role of TLR2 in mediating neuroinflammation and neuronal damage [45], we have previously demonstrated that a single intraperitoneal injection of the TLR2 agonist Pam 3 CSK 4 revealed a robust increase in the WBC count in the CSF in mice on PND8 [38], and repeated administration of Pam 3 CSK 4 induced brain injury in newborn animals [19].…”

Cerebral hypoxia–ischemia increases toll-like receptor 2 and 4 expression in the hippocampus of neonatal rats

“…Moreover, TLR2 and TLR4 were found to be important in the pathological progression of cerebral ischemia and reperfusion [9,10]. However, a paucity of studies have investigated the role of TLRs in neonatal ischemic brain injury [11,12].…”