title: Microglia and motor neurons during disease progression in the SOD1G93A mouse model of amyotrophic lateral sclerosis: changes in arginase1 and inducible nitric oxide synthase.
abstract: BACKGROUND
  Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting the motor system. Although the etiology of the disease is not fully understood, microglial activation and neuroinflammation are thought to play a role in disease progression.
  
  
  METHODS
  We examined the immunohistochemical expression of two markers of microglial phenotype, the arginine-metabolizing enzymes inducible nitric oxide synthase (iNOS) and arginase1 (Arg1), in the spinal cord of a mouse model carrying an ALS-linked mutant human superoxide dismutase transgene (SOD1(G93A)) and in non-transgenic wild-type (WT) mice. Immunolabeling for iNOS and Arg1 was evaluated throughout disease progression (6 to 25 weeks), and correlated with body weight, stride pattern, wire hang duration and ubiquitin pathology. For microglia and motor neuron counts at each time point, SOD1(G93A) and WT animals were compared using an independent samples t-test. A Welch t-test correction was applied if Levene's test showed that the variance in WT and SOD1G93A measurements was substantially different.
  
  
  RESULTS
  Disease onset, measured as the earliest change in functional parameters compared to non-transgenic WT mice, occurred at 14 weeks of age in SOD1(G93A) mice. The ventral horn of the SOD1(G93A) spinal cord contained more microglia than WT from 14 weeks onwards. In SOD1(G93A) mice, Arg1-positive and iNOS-positive microglia increased 18-fold and 7-fold, respectively, between 10 and 25 weeks of age (endpoint) in the lumbar spinal cord, while no increase was observed in WT mice. An increasing trend of Arg1- and iNOS-expressing microglia was observed in the cervical spinal cords of SOD1(G93A) mice. Additionally, Arg1-negative motor neurons appeared to selectively decline in the spinal cord of SOD1(G93A) mice, suggesting that Arg1 may have a neuroprotective function.
  
  
  CONCLUSIONS
  This study suggests that the increase in spinal cord microglia occurs around and after disease onset and is preceded by cellular pathology. The results show that Arg1 and iNOS, thought to have opposing inflammatory properties, are upregulated in microglia during disease progression and that Arg1 in motor neurons may confer protection from disease processes. Further understanding of the neuroinflammatory response, and the Arg1/iNOS balance in motor neurons, may provide suitable therapeutic targets for ALS.
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Lewis
authors.forename: Anna L
authors.initials: AL
authors.lastname: Rasmussen
authors.forename: William
authors.initials: W
authors.lastname: Bennett
authors.forename: Anna
authors.initials: A
authors.lastname: King
authors.forename: Adrian K
authors.initials: AK
authors.lastname: West
authors.forename: Roger S
authors.initials: RS
authors.lastname: Chung
authors.affiliation: Wicking Dementia Research and Education Centre, University of Tasmania, Hobart, TAS, Australia. Inn.Chuah@utas.edu.au.
authors.forename: Meng Inn
authors.initials: MI
authors.lastname: Chuah
mesh_terms: D000367:Age Factors; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000401:mortality / Q000473:pathology* / Q000503:physiopathology; D000818:Animals; D001119:Arginase / Q000235:genetics / Q000378:metabolism*; D001835:Body Weight / Q000235:genetics; D004195:Disease Models, Animal; D018450:Disease Progression; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000378:metabolism*; D009046:Motor Neurons / Q000378:metabolism*; D053580:Muscle Strength / Q000235:genetics; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism*; D011597:Psychomotor Performance / Q000502:physiology; D013116:Spinal Cord / Q000473:pathology; D013482:Superoxide Dismutase / Q000235:genetics; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D025801:Ubiquitin; D052247:Nitric Oxide Synthase Type II; C470429:SOD1 G37R protein, mouse; D013482:Superoxide Dismutase; C544448:Arg1 protein, mouse; D001119:Arginase