Systemic inflammation in early neonatal mice induces transient and lasting neurodegenerative effects.
BACKGROUND
The inflammatory mediator lipopolysaccharide (LPS) has been shown to induce acute gliosis in neonatal mice. However, the progressive effects on the murine neurodevelopmental program over the week that follows systemic inflammation are not known. Thus, we investigated the effects of repeated LPS administration in the first postnatal week in mice, a condition mimicking sepsis in late preterm infants, on the developing central nervous system (CNS).


METHODS
Systemic inflammation was induced by daily intraperitoneal administration (i.p.) of LPS (6 mg/kg) in newborn mice from postnatal day (PND) 4 to PND6. The effects on neurodevelopment were examined by staining the white matter and neurons with Luxol Fast Blue and Cresyl Violet, respectively. The inflammatory response was assessed by quantifying the expression/activity of matrix metalloproteinases (MMP), toll-like receptor (TLR)-4, high mobility group box (HMGB)-1, and autotaxin (ATX). In addition, B6 CX3CR1(gfp/+) mice combined with cryo-immunofluorescence were used to determine the acute, delayed, and lasting effects on myelination, microglia, and astrocytes.


RESULTS
LPS administration led to acute body and brain weight loss as well as overt structural changes in the brain such as cerebellar hypoplasia, neuronal loss/shrinkage, and delayed myelination. The impaired myelination was associated with alterations in the proliferation and differentiation of NG2 progenitor cells early after LPS administration, rather than with excessive phagocytosis by CNS myeloid cells. In addition to disruptions in brain architecture, a robust inflammatory response to LPS was observed. Quantification of inflammatory biomarkers revealed decreased expression of ATX with concurrent increases in HMGB1, TLR-4, and MMP-9 expression levels. Acute astrogliosis (GFAP(+) cells) in the brain parenchyma and at the microvasculature interface together with parenchymal microgliosis (CX3CR1(+) cells) were also observed. These changes preceded the migration/proliferation of CX3CR1(+) cells around the vessels at later time points and the subsequent loss of GFAP(+) astrocytes.


CONCLUSIONS
Collectively, our study has uncovered a complex innate inflammatory reaction and associated structural changes in the brains of neonatal mice challenged peripherally with LPS. These findings may explain some of the neurobehavioral abnormalities that develop following neonatal sepsis.
Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. filipacardoso@ff.ulisboa.pt.
Filipa L
FL
Cardoso
National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive, Bethesda, MD, 20892-1430, USA. herzjn@ninds.nih.gov.
Jasmin
J
Herz
Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. amaf@ff.ulisboa.pt.|Department of Biochemistry and Human Biology, Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. amaf@ff.ulisboa.pt.
Adelaide
A
Fernandes
Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. jrocha@ff.ulisboa.pt.
João
J
Rocha
Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. bsepodes@ff.ulisboa.pt.
Bruno
B
Sepodes
Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. abrito@ff.ulisboa.pt.|Department of Biochemistry and Human Biology, Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. abrito@ff.ulisboa.pt.
Maria A
MA
Brito
National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive, Bethesda, MD, 20892-1430, USA. mcgavernd@ninds.nih.gov.
Dorian B
DB
McGavern
Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. dbrites@ff.ulisboa.pt.|Department of Biochemistry and Human Biology, Faculdade de Farmácia, Universidade de Lisboa, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal. dbrites@ff.ulisboa.pt.
Dora
D
Brites
D000367:Age Factors; D000781:Anethole Trithione / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001835:Body Weight / Q000187:drug effects; D000073883:CX3C Chemokine Receptor 1; D002531:Cerebellum / Q000002:abnormalities; D003711:Demyelinating Diseases / Q000139:chemically induced / Q000150:complications; D002658:Developmental Disabilities / Q000209:etiology; D005786:Gene Expression Regulation / Q000187:drug effects; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D024243:HMGB1 Protein / Q000378:metabolism; D007249:Inflammation / Q000139:chemically induced / Q000150:complications*; D008070:Lipopolysaccharides / Q000633:toxicity; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000473:pathology; D004676:Myelin Basic Protein / Q000378:metabolism; D009421:Nervous System Malformations / Q000209:etiology; D019636:Neurodegenerative Diseases / Q000209:etiology*; D019707:Receptors, Chemokine / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D051197:Toll-Like Receptor 4 / Q000378:metabolism
C558259:4-hydroxy-anethole trithione; D000073883:CX3C Chemokine Receptor 1; C471885:Cx3cr1 protein, mouse; D024243:HMGB1 Protein; D008070:Lipopolysaccharides; C499047:Mbp protein, mouse; D004676:Myelin Basic Protein; D019707:Receptors, Chemokine; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D049452:Green Fluorescent Proteins; D000781:Anethole Trithione