Elsevier

Psychoneuroendocrinology

Volume 38, Issue 12, December 2013, Pages 3102-3114
Psychoneuroendocrinology

TNF-α and its receptors modulate complex behaviours and neurotrophins in transgenic mice

https://doi.org/10.1016/j.psyneuen.2013.09.010Get rights and content

Summary

Tumour necrosis factor-α (TNF-α) plays an important role not only in immunity but also in the normal functioning of the central nervous system (CNS). At physiological levels, studies have shown TNF-α is essential to maintain synaptic scaling and thus influence learning and memory formation while also playing a role in modulating pathological states of anxiety and depression. TNF-α signals mainly through its two receptors, TNF-R1 and TNF-R2, however the exact role that these receptors play in TNF-α mediated behavioural phenotypes is yet to be determined.

Methods

We have assessed TNF−/−, TNF-R1−/− and TNF-R2−/− mice against C57BL/6 wild-type (WT) mice from 12 weeks of age in order to evaluate measures of spatial memory and learning in the Barnes maze (BM) and Y-maze, as well as other behaviours such as exploration, social interaction, anxiety and depression-like behaviour in a battery of tests. We have also measured hippocampal and prefrontal cortex levels of the neurotrophins nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) as well as used immunohistochemical analyses to measure number of proliferating cells (Ki67) and immature neurons (DCX) within the dentate gyrus.

Results

We have shown that young adult TNF−/− and TNF-R1−/− mice displayed impairments in learning and memory in the BM and Y-maze, while TNF-R2−/− mice showed good memory but slow learning in these tests. TNF−/−and TNF-R2−/− mice also demonstrated a decrease in anxiety like behaviour compared to WT mice. ELISA analyses showed TNF−/− and TNF-R2−/− mice had lower levels of NGF compared to WT mice.

Conclusion

These results indicate that while lack of TNF-α can decrease anxiety-like behaviour in mice, certain basal levels of TNF-α are required for the development of normal cognition. Furthermore our results suggest that both TNF-R1 and TNF-R2 signalling play a role in normal CNS function, with knockout of either receptor impairing cognition on the Barnes maze.

Introduction

Tumour necrosis factor alpha (TNF-α) is a pro-inflammatory cytokine showing biological effects in the central nervous system (CNS) (Stellwagen et al., 2005, McAfoose and Baune, 2009, Clark et al., 2010, Baune et al., 2012) In the CNS, TNF-α is produced by the resident immune cells of the CNS, the microglia and astrocytes, as well as by certain neuronal populations (Li et al., 2008, McCoy and Tansey, 2008). This cytokine is shown to cross the blood–brain barrier (BBB) in conditions of systemic inflammation (Pan and Kastin, 2002) and is known to play a role in activating the hypothalamic pituitary adrenal (HPA) axis by stimulating the corticotrophin-releasing hormone and increasing levels of corticosterone (Bernardini et al., 1990). High levels of TNF-α in the dorsolateral prefrontal cortex have also been linked to major depressive disorder (Dean et al., 2010) and increased expression of TNF-α were also observed in murine models of depressive like behaviour and chronic mild stress (You et al., 2011, Kaster et al., 2012).

Beyond its involvement in various CNS pathologies, TNF-α may be is required for maintaining certain physiological processes within the CNS (Stellwagen et al., 2005). TNF-α has been shown to play a role in mediating synaptic scaling (Stellwagen et al., 2005), and was found to be essential to early cognitive development (McAfoose et al., 2009). Constitutive levels of TNF-α are linked to increased neurogenesis (Iosif et al., 2006) and TNF-α is also shown to influence the expression of neurotrophins, such as nerve growth factor (NGF) (Takei and Laskey, 2008) and brain derived neurotrophic factor (BDNF) (Golan et al., 2004). Indeed, modulation of neurotrophins may explain the finding that young adult mice that lack TNF-α (TNF−/− mice) exhibit cognitive impairment (Baune et al., 2008). Furthermore, TNF-α can play an integral part in modulating anxiety like behaviour as well as in fear conditioning (Yamada et al., 2000, Simen et al., 2006).

TNF-α signals through two main receptors, TNF-R1 and TNF-R2, which are thought to have disparate functions, with suggestions that activation of TNF-R1 is neurodegenerative, whilst activation of TNF-R2 is neuroprotective (Shu et al., 1996, Kassiotis and Kollias, 2001, Fontaine et al., 2002). This is because signalling through the TNF-R1 pathway, which primarily occurs via soluble TNF-α, initiates the activation of caspases leading to apoptosis, due to the presence of a cytoplasmic ‘death domain’. In the brain, TNF-R1 is widely expressed by astrocytes, oligodendrocytes and microglia, whereas only microglial cells express TNF-R2 (Dopp et al., 1997). In immunologically unchallenged conditions TNF-R1 appears to be more abundantly expressed by neurons in the brain while basal levels of TNF-R2 are expressed only in the cortex, cerebellum and tegmentum (Bette et al., 2003). In contrast, activation of the TNF-R2 pathway, which primarily occurs via transmembrane TNF-α, promotes cell survival, through inhibition of caspase activation (Horiuchi et al., 2010). Intriguingly, the distinction between these two signalling pathways does not appear to be as clear cut as previously thought, with an earlier study demonstrating that TNF−/−, TNF-R1−/− and TNF-R2−/− mice all exhibited cognitive deficits (Baune et al., 2008), suggesting that signalling through the receptors is not exclusively neurodegenerative or neuroprotective.

Therefore, to further explore the role of TNF-R1 and TNF-R2 signalling in behavioural responses, we have performed an extensive behavioural battery assessing cognition-like behaviour (learning and memory), social interactions, exploratory activity, anxiety-like behaviour and depression-like behaviour in young adult (12-week old) TNF−/−, TNF-R1−/− and TNF-R2−/− transgenic mice. Furthermore, to determine whether behavioural changes in these transgenic mice relate to underlying changes in neurotrophins, these parameters were also investigated. While previous studies have investigated the effects of genetic deletion of TNF-α and its receptors on cognition-like (Baune et al., 2008) and anxiety-like behaviours (Yamada et al., 2000, Simen et al., 2006), this is the first study to provide a comprehensive description of a wider range of behavioural phenotypes, including cognition-, anxiety- and depression-like behaviours extending into sociability and exploratory behaviour, governed by TNF-α and its receptors, while considering molecular mechanisms of neurotrophins and neurogenesis expression to influence such behaviour.

Section snippets

Mouse strains

The gene-targeted C57BL/6 mouse strain deficient for TNF-α (TNF−/−) (n = 14, seven male, seven female mice) was generated on a genetically pure C57BL/6 background as described previously (Korner et al., 1997) and has been bred in-house for over five generations. The C57BL/6 (WT) mice (Jackson stock number: 000664) were purchased from the University of Adelaide breeding facility (n = 21, 10 male, 11 female). TNF-R1−/− (Jackson stock number: 003242) (Peschon et al., 1998) and TNF-R2−/− mice (Jackson

Mean weight, age and sex

Mean age of all animals used was 12 weeks at the start of behavioural testing. The average weight of mice was 24.0 ± 1.4 g for male mice and 18.0 ± 1.5 g for female mice of all strains and no significant differences were observed between strains as analysed by Kruskal–Wallis test.

To minimise potential gender-specific effects in behaviour that could arise from genetic deletion of TNF-α and TNF-α receptor related genes, roughly equal numbers of male and female mice were used in the present study. No

Discussion

In this study we have shown that TNF−/− mice displayed impairments in memory in the Barnes maze and Y-maze, while TNF-R2−/− mice showed good memory but slow learning in these tests. TNF-R2−/− and TNF−/− mice also showed low levels of anxiety like behaviour. All strains of mice demonstrated a significant preference for social situations over non-social ones, however only WT and TNF−/− mice showed a significant preference for social novelty. Analysis of neurotrophin levels in the prefrontal

Role of funding source

This study is supported by the National Health and Medical Research Council Australia (APP1003788 to BTB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Conflict of interest

None declared.

References (58)

  • C. Kopp

    Locomotor activity rhythm in inbred strains of mice: implications for behavioural studies

    Behav. Brain Res.

    (2001)
  • H.V. Lad et al.

    Behavioural battery testing: evaluation and behavioural outcomes in 8 inbred mouse strains

    Physiol. Behav.

    (2010)
  • J. McAfoose et al.

    Evidence for a cytokine model of cognitive function

    Neurosci. Biobehav. Rev.

    (2009)
  • J. McAfoose et al.

    The effects of TNF deficiency on age-related cognitive performance

    Psychoneuroendocrinology

    (2009)
  • K. Palin et al.

    TNFalpha-induced sickness behavior in mice with functional 55 kD TNF receptors is blocked by central IGF-I

    J. Neuroimmunol.

    (2007)
  • W. Pan et al.

    TNFalpha transport across the blood–brain barrier is abolished in receptor knockout mice

    Exp. Neurol.

    (2002)
  • H. Sei et al.

    Differential effect of short-term REM sleep deprivation on NGF and BDNF protein levels in the rat brain

    Brain Res.

    (2000)
  • B.B. Simen et al.

    TNFalpha signaling in depression and anxiety: behavioral consequences of individual receptor targeting

    Biol. Psychiatry

    (2006)
  • Y. Takei et al.

    Interpreting crosstalk between TNF-alpha and NGF: potential implications for disease

    Trends Mol. Med.

    (2008)
  • K. Yamada et al.

    Neurobehavioral alterations in mice with a targeted deletion of the tumor necrosis factor-alpha gene: implications for emotional behavior

    J. Neuroimmunol.

    (2000)
  • Z. You et al.

    Pro- and anti-inflammatory cytokines expression in rat's brain and spleen exposed to chronic mild stress: involvement in depression

    Behav. Brain Res.

    (2011)
  • C. Zhao et al.

    Mechanisms and functional implications of adult neurogenesis

    Cell

    (2008)
  • V. Barker et al.

    TNFalpha contributes to the death of NGF-dependent neurons during development

    Nat. Neurosci.

    (2001)
  • B.T. Baune et al.

    Tumour necrosis factor alpha mediated mechanisms of cognitive dysfunction

    Trends Neurosci.

    (2012)
  • B.T. Baune et al.

    Cognitive dysfunction in mice deficient for TNF- and its receptors

    Am. J. Med. Genet. B: Neuropsychiatr. Genet.

    (2008)
  • E.C. Beattie et al.

    Control of synaptic strength by glial TNFalpha

    Science

    (2002)
  • R. Bernardini et al.

    Interactions between tumor necrosis factor-alpha, hypothalamic corticotropin-releasing hormone, and adrenocorticotropin secretion in the rat

    Endocrinology

    (1990)
  • M. Bette et al.

    Constitutive expression of p55TNFR mRNA and mitogen-specific up-regulation of TNF alpha and p75TNFR mRNA in mouse brain

    J. Comp. Neurol.

    (2003)
  • A.J. Bruce et al.

    Altered neuronal and microglial responses to excitotoxic and ischemic brain injury in mice lacking TNF receptors

    Nat. Med.

    (1996)
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