Experimental Herpes simplex virus encephalitis: MMP-TIMP disbalance in the chronic phase of disease

Introduction: Herpes simplex virus encephalitis (HSVE) remains a disease with high mortality and severe long-term neuropsychological impairment despite early antiviral treatment. Secondary mechanisms of neuronal injury other than viral replication have been proposed. Matrix metalloproteinases 2 and 9 (MMP2 and MMP9) participate in the degradation of the basal membrane and in the remodeling of the extracellular matrix. MMP activity is regulated by the tissue inhibitors of metalloproteinases (TIMPs), and MMP2 activation is regulated by MMP14. A disbalance in the extracellular matrix turnover may contribute to ongoing brain injury.

Aim: The aim of our study was to analyze the expression of MMP14 and TIMP2 and the enzymatic activity of MMP2 and MMP9 in a well described murine model of HSVE, in the acute as well as in the chronic phase of disease.

Methods: Animals were intranasally inoculated with 10⁵ pfu of HSV-1 strain F, negative control animals were sham-inoculated with sterile saline. Brains were microsurgically removed and snap frozen for further analysis. Viral burden in brain tissue was quantified with dilutional PCR and was confirmed in infected animals. After mRNA extraction reverse transcriptase PCR was performed. Expression of MMP14,TIMP2 and GAPDH was analyzed using real time PCR. MMPs were extracted and lytic activity measured with SDS-PAGE zymography, and densitometrically analyzed using image processing software.

Results: Enhanced MMP2 and MMP9 dependent gelatinolysis was observed in untreated animals as compared to negative controls. MMP14 mRNA expression remained unchanged in the acute and chronic phase of disease. TIMP2 mRNA up-regulation was observed in the chronic phase of disease.

Conclusion: An MMP/TIMP disbalance may be an important factor leading to permanent brain injury in HSVE.