Recovery from an acute systemic and central LPS-inflammation challenge is affected by mouse sex and genetic background

Abstract

Genetic and sexual factors influence the prevalence and the pathogenesis of many inflammatory disorders. In this study their relevance on the peripheral and central inflammatory status induced by a peripheral injection of lipopolysaccharide (LPS) was evaluated. BALB/c and CD-1 male and female mice were intraperitoneally injected with LPS. Spleens and brains were collected 2 and 72 hours later to study the levels of IL-6, TNF-α and IL-1β. Percentage of microglia and astrocytes was determined in the cortex and hippocampus. Locomotor activity was registered before and during the 72 hours after LPS-treatment. Two hours after LPS-injection, a peripheral increase of the three cytokines was found. In brains, LPS increased TNF-α only in males with higher levels in CD-1 than BALB/c. IL-1β increased only in CD-1 males. IL-6 increased in both strains with lower levels in BALB/c females. Peripheral and central levels of cytokines decline 72 hrs after LPS-treatment whilst a significantly increase of Iba-1 expression was detected. A dramatic drop of the locomotor activity was observed immediately after LPS injection. Our results show that acute systemic administration of LPS leads to peripheral and central increase of pro-inflammatory cytokines and microglia activation, in a strain and sex dependent manner.

Fig 1. Cytokine levels in CD-1 and BALB/c male and female mice two hours after LPS administration.

†Mean ±SD of the level of cytokines (pg/mg of total protein) in spleen and brains of non-treated, saline or LPS-treated in groups of three to five BALB/c and CD-1 male and female mice. Different literals indicates statistically significant (P<0.05) differences between values of each column using an unpaired t test with Welch’s corrections.

Fig 2. Immunohistological staining and quantification of Iba-1, 72 hrs after i.p. injection of LPS.

A) Representative immunofluorescence of 30 μm coronal sections stained with anti-Iba-1 antibodies in two cornu ammonis (CA1 and CA2) regions. The pictures derive from saline and LPS-treated mice. B) Mean ± standard deviation of the percentage of Iba-1 using Image J software (National Institute of Health, Bethesda, MD, USA). The effects of the LPS in Iba-1 expression in each region were compared. Data labeled with the same letter are not significantly different from each other, whereas those with different letters are significantly different.

Fig 3. Immunohistological staining and quantification of Iba-1, 72 hrs after i.p. injection of LPS.

A) Representative immunofluorescence of 30 μm coronal sections stained with anti-Iba-1 antibodies in two regions the cortex (R1 and R2). The pictures derive from saline and LPS-treated mice. B) Mean ± standard deviation of the percentage of Iba-1 using Image J software (National Institute of Health, Bethesda, MD, USA). The effects of the LPS in Iba-1 expression in each region were compared. Data labeled with the same letter are not significantly different from each other, whereas those with different letters are significantly different. No signal was detected in negative controls using TBS-2% BSA instead of the primary antibody.

Fig 4. BALB/c and CD1 mice recovery of locomotor activity.

Shapes mark mean locomotor activity measured at 24 hrs each day. Whiskers show SEM. Asterisks mark significant difference respect to saline and untreated controls.