Impact of Aging, Sex, and Species on the mRNA Expression of Matrix Metalloproteinases Following Ischemic Stroke

Abstract

Matrix metalloproteinase (MMP) expression and function are highly context dependent, varying across physiological and pathological conditions. We previously documented the expression profiles of select MMPs in the ischemic brains of young male rodents. However, aging is a major risk factor for stroke in humans and is associated with vasculature alterations, increased oxidative stress, and elevated inflammation. In addition, sex differences have been reported in stroke incidence and severity. Despite this, the effects of age, sex, and species on brain MMP gene expression after cerebral ischemia/reperfusion (I/R) has not been systematically examined. Therefore, we investigated how age, sex, and species influence the mRNA expression of all known MMPs (22 total) in the brain following cerebral I/R. Moderate-to-severe neurological deficits were induced by transient middle cerebral artery occlusion (MCAO) followed by reperfusion in young and aged male and female C57BL/6 mice and in young male Sprague-Dawley rats. Brain tissue from the ipsilateral (ischemic) hemisphere was collected on post-MCAO day 1, and MMP mRNA levels were quantified by real-time PCR and expressed as fold change relative to the sham control group. Across species, MMP-3, MMP-8, MMP-12, MMP-13, MMP-19, MMP-20, and MMP-27 were upregulated in both rats and mice. Species-specific increases were also observed: MMP-1, MMP-7, MMP-9, MMP-14, MMP-21, and MMP-25 were upregulated only in rats, whereas MMP-10 was upregulated only in mice. The most strongly upregulated MMPs were MMP-12 in rats and MMP-3, MMP-10, and MMP-12 in mice. By contrast, MMP-15 and MMP-17 were downregulated in both species, whereas MMP-23 and MMP-24 were downregulated only in rats and mice, respectively. Within mice, MMP-3, MMP-10, MMP-12, MMP-19, MMP-20, and MMP-21 increased in both sexes and age groups, except for MMP-19 in aged males and MMP-21 in young males. MMP-14 increased only in females (young and aged), whereas MMP-27 increased only in males (young and aged). Notably, MMP-3, MMP-10, and MMP-12 were the three most highly upregulated MMPs in both male and female mice regardless of age. Overall MMP mRNA expression levels were higher in aged male mice and lower in aged female mice relative to sex-matched young mice. Among all MMPs examined, MMP-12 showed the most marked upregulation across species and, within mice, across age groups and sexes. Collectively, these findings demonstrate that brain MMP gene expression after cerebral I/R is modulated by age, sex, and species, underscoring the importance of incorporating these biological variables when targeting MMPs individually or in combination in preclinical rodent stroke models.