Matrix Metalloproteinase-9 Gene Knock-out Protects the Immature Brain after Cerebral Hypoxia–Ischemia

Abstract

Inhibition of matrix metalloproteinase-9 (MMP-9) protects the adult brain after cerebral ischemia. However, the role of MMP-9 in the immature brain after hypoxia-ischemia (HI) is unknown. We exposed MMP-9 (Ϫ/Ϫ) [MMP-9 knock-out (KO)] and wild-type (WT) mice to HI on postnatal day 9. HI was induced by unilateral ligation of the left carotid artery followed by hypoxia (10% O 2 ; 36°C). Gelatin zymography showed that MMP-9 activity was transiently increased at 24 h after HI in the ipsilateral hemisphere and MMP-9-positive cells were colocalized with activated microglia. Seven days after 50 min of HI, cerebral tissue volume loss was reduced in MMP-9 KO (21.8 Ϯ 1.7 mm 3 ; n ϭ 22) compared with WT (32.3 Ϯ 2.1 mm 3 ; n ϭ 22; p Ͻ 0.001) pups, and loss of white-matter components was reduced in MMP-9 KO compared with WT pups (neurofilament: WT, 50.9 Ϯ 5.4%; KO, 18.4 Ϯ 3.1%; p Ͻ 0.0001; myelin basic protein: WT, 57.5 Ϯ 5.8%; KO, 23.2 Ϯ 3.5%; p ϭ 0.0001). The neuropathological changes were associated with a delayed and diminished leakage of the blood-brain barrier (BBB) and a decrease in inflammation in MMP-9-deficient animals. In contrast, the neuroprotective effects after HI in MMP-9-deficient animals were not linked to either caspase-dependent (caspase-3 and cytochrome c) or caspase-independent (apoptosis-inducing factor) processes. This study demonstrates that excessive activation of MMP-9 is deleterious to the immature brain, which is associated with the degree of BBB leakage and inflammation. In contrast, apoptosis does not appear to be a major contributing factor.

Increased MMP-9 and TIMP-1 in mouse neonatal brain and plasma and in human neonatal plasma after hypoxia–ischemia: a potential marker of neonatal encephalopathy

“…Excitotoxic and inflammatory processes are involved in both the early phase of brain ischemia and the regulation of MMP expression. However, one cannot rule out the possibility that the severity of tissue damage is a factor contributing to the increase in MMP-9 and TIMP-1 expression in HI mice, given that brain lesions are known to be more severe from a histological viewpoint in the HI model than in the excitotoxin models (7,18).…”

“…This balance between the two molecules is thought to reduce brain damage in HI events by protecting the blood-brain barrier (7). MMP inhibition provides neuroprotection against HI in the developing brain (21).…”

“…Recent studies in adult MMP-9 knockout mice have demonstrated the key role played by this metalloproteinase in the pathophysiology of traumatic and hypoxic-ischemic (HI) brain injury (6). Concordantly, MMP-9 has been shown to have deleterious effects in the immature brain after HI injury (7). Several of these studies demonstrated a significant increase in MMP-9 expression in the central nervous system within the first 24 h after the insult.…”

“…P9 in C57Bl/6 mice by unilateral ligation of the left carotid followed by induced hypoxia (10% oxygen in nitrogen, humidified, for 50 min) as previously described (7,15). The neonatal mice were killed at 1, 3, 6, 24, and 48 h and 3, 4 and 5 days after HI.…”

MMP9 Limits Apoptosis and Stimulates Branching Morphogenesis During Kidney Development

“…29 On the other hand, MMP9 possesses a variety of nonmatrix substrates whose cleavage may protect from apoptosis. 8 Decreased apoptosis was observed in MMP9-deficient mice after partial hepatectomy 30 and cerebral hypoxia-ischemia, 31 although the underlying mechanisms were poorly understood. In contrast, we found that MMP9 was protective in acute kidney injury by markedly reducing apoptosis and thus accelerating renal function recovery.…”