John D. Lee

Dysregulation of the complement cascade in the hSOD1G93A transgenic mouse model of amyotrophic lateral sclerosis.

BackgroundComponents of the innate immune complement system have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS); however, a comprehensive examination of complement expression in this disease has not been performed. This study therefore aimed to determine the expression of complement components (C1qB, C4, factor B, C3/C3b, C5 and CD88) and regulators (CD55 and CD59a) in the lumbar spinal cord of hSOD1G93A mice during defined disease stages.MethodshSOD1G93A and wild-type mice were examined at four different ages of disease progression. mRNA and protein expression of complement components and regulators were examined using quantitative PCR, western blotting and ELISA. Localisation of complement components within lumbar spinal cord was investigated using immunohistochemistry. Statistical differences between hSOD1G93A and wild-type mice were analysed using a two-tailed t-test at each stage of disease progression.ResultsWe found several early complement factors increased as disease progressed, whilst complement regulators decreased; suggesting overall increased complement activation through the classical or alternative pathways in hSOD1G93A mice. CD88 was also increased during disease progression, with immunolocalisation demonstrating expression on motor neurons and increasing expression on microglia surrounding the regions of motor neuron death.ConclusionsThese results indicate that local complement activation and increased expression of CD88 may contribute to motor neuron death and ALS pathology in the hSOD1G93A mouse. Hence, reducing complement-induced inflammation could be an important therapeutic strategy to treat ALS.

Absence of toll-like receptor 4 (TLR4) extends survival in the hSOD1 G93A mouse model of amyotrophic lateral sclerosis

BackgroundAmyotrophic lateral sclerosis (ALS) is a devastating late onset neurodegenerative disorder that is characterised by the progressive loss of upper and lower motor neurons. The mechanisms underlying ALS pathogenesis are unclear; however, there is emerging evidence the innate immune system, including components of the toll-like receptor (TLR) system, may drive disease progression. For example, toll-like receptor 4 (TLR4) antagonism in a spontaneous ‘wobbler mouse’ model of ALS increased motor function, associated with a decrease in microglial activation. This study therefore aimed to extend from these findings and determine the expression and function of TLR4 signalling in hSOD1G93A mice, the most widely established preclinical model of ALS.FindingsTLR4 and one of its major endogenous ligands, high-mobility group box 1 (HMGB1), were increased during disease progression in hSOD1G93A mice, with TLR4 and HMGB1 expressed by activated microglia and astrocytes. hSOD1G93A mice lacking TLR4 showed transient improvements in hind-limb grip strength and significantly extended survival when compared to TLR4-sufficient hSOD1G93A mice.ConclusionThese results suggest that enhanced glial TLR4 signalling during disease progression contributes to end-stage ALS pathology in hSOD1G93A mice.

Therapeutic targeting of complement to modify disease course and improve outcomes in neurological conditions

The recognition that complement proteins are abundantly present and can have pathological roles in neurological conditions offers broad scope for therapeutic intervention. Accordingly, an increasing number of experimental investigations have explored the potential of harnessing the unique activation pathways, proteases, receptors, complexes, and natural inhibitors of complement, to mitigate pathology in acute neurotrauma and chronic neurodegenerative diseases. Here, we review mechanisms of complement activation in the central nervous system (CNS), and explore the effects of complement inhibition in cerebral ischemic-reperfusion injury, traumatic brain injury, spinal cord injury, Alzheimers disease, amyotrophic lateral sclerosis, Parkinsons disease and Huntingtons disease. We consider the challenges and opportunities arising from these studies. As complement therapies approach clinical translation, we provide perspectives on how promising complement-targeted therapeutics could become part of novel and effective future treatment options to improve outcomes in the initiation and progression stages of these debilitating CNS disorders.

Cortical synaptic and dendritic spine abnormalities in a presymptomatic TDP-43 model of amyotrophic lateral sclerosis

Layer V pyramidal neurons (LVPNs) within the motor cortex integrate sensory cues and co-ordinate voluntary control of motor output. In amyotrophic lateral sclerosis (ALS) LVPNs and spinal motor neurons degenerate. The pathogenesis of neural degeneration is unknown in ALS; 10% of cases have a genetic cause, whereas 90% are sporadic, with most of the latter showing TDP-43 inclusions. Clinical and experimental evidence implicate excitotoxicity as a prime aetiological candidate. Using patch clamp and dye-filling techniques in brain slices, combined with high-resolution confocal microscopy, we report increased excitatory synaptic inputs and dendritic spine densities in early presymptomatic mice carrying a TDP-43Q331K mutation. These findings demonstrate substantive alterations in the motor cortex neural network, long before an overt degenerative phenotype has been reported. We conclude that increased excitatory neurotransmission is a common pathophysiology amongst differing genetic cases of ALS and may be of relevance to the 95% of sporadic ALS cases that exhibit TDP-43 inclusions.

Role for terminal complement activation in amyotrophic lateral sclerosis disease progression

Lobsiger et al. (1) recently demonstrated that superoxide dismutase 1 (SOD1) transgenic mice deficient in complement components C1q and C3 do not have extended survival, concluding that global complement activation does not affect overall disease in amyotrophic lateral sclerosis (ALS). Complement activation has long been implicated in the pathogenesis of ALS, with numerous clinical and animal studies demonstrating strong complement factor up-regulation, including C1q and C3, in regions of motor neuron death (2). Intriguingly, in the study by Lobsiger et al. C3- (and C1q-) deleted SOD1 mice did not show alterations in survival or motor neuron estimates, and this is interpreted by the authors as complement activation not contributing to ALS mice neurotoxicity. Indeed, in figure S1 of their article, Lobsiger et al. present three C3-dependent pathways of complement activation (classic, lectin, and alternative). However, one point missing in this report, and perhaps overlooked by the casual reader, is that there is now a well-described fourth pathway of complement activation, termed the “extrinsic pathway,” which can bypass the traditional upstream activation pathways that are reliant on complement factor C3.

Pharmacological inhibition of complement C5a-C5a1 receptor signalling ameliorates disease pathology in the hSOD1G93A mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal and rapidly progressing motor neuron disease without effective treatment. The complement system is up‐regulated in ALS, with recent studies indicating that the activation product C5a accelerates disease progression via the C5a1 receptor (C5aR1). We therefore examined the therapeutic effect of C5a1 receptor antagonism in hSOD1G93A mice, the most widely used preclinical model of ALS.

Complement C5aR1 Signaling Promotes Polarization and Proliferation of Embryonic Neural Progenitor Cells through PKCζ.

The complement system, typically associated with innate immunity, is emerging as a key controller of nonimmune systems including in development, with recent studies linking complement mutations with neurodevelopmental disease. A key effector of the complement response is the activation fragment C5a, which, through its receptor C5aR1, is a potent driver of inflammation. Surprisingly, C5aR1 is also expressed during early mammalian embryogenesis; however, no clearly defined function is ascribed to C5aR1 in development. Here we demonstrate polarized expression of C5aR1 on the apical surface of mouse embryonic neural progenitor cells in vivo and on human embryonic stem cell-derived neural progenitors. We also show that signaling of endogenous C5a during mouse embryogenesis drives proliferation of neural progenitor cells within the ventricular zone and is required for normal brain histogenesis. C5aR1 signaling in neural progenitors was dependent on atypical protein kinase C ζ, a mediator of stem cell polarity, with C5aR1 inhibition reducing proliferation and symmetric division of apical neural progenitors in human and mouse models. C5aR1 signaling was shown to promote the maintenance of cell polarity, with exogenous C5a increasing the retention of polarized rosette architecture in human neural progenitors after physical or chemical disruption. Transient inhibition of C5aR1 during neurogenesis in developing mice led to behavioral abnormalities in both sexes and MRI-detected brain microstructural alterations, in studied males, demonstrating a requirement of C5aR1 signaling for appropriate brain development. This study thus identifies a functional role for C5a–C5aR1 signaling in mammalian neurogenesis and provides mechanistic insight into recently identified complement gene mutations and brain disorders. SIGNIFICANCE STATEMENT The complement system, traditionally known as a controller of innate immunity, now stands as a multifaceted signaling family with a broad range of physiological actions. These include roles in the brain, where complement activation is associated with diseases, including epilepsy and schizophrenia. This study has explored complement regulation of neurogenesis, identifying a novel relationship between the complement activation peptide C5a and the neural progenitor proliferation underpinning formation of the mammalian brain. C5a was identified as a regulator of cell polarity, with inhibition of C5a receptors during embryogenesis leading to abnormal brain development and behavioral deficits. This work demonstrates mechanisms through which dysregulation of complement causes developmental disease and highlights the potential risk of complement inhibition for therapeutic purposes in pregnancy.

Impairments to the GH-IGF-I Axis in hSOD1G93A Mice Give Insight into Possible Mechanisms of GH Dysregulation in Patients with Amyotrophic Lateral Sclerosis

GH deficiency has been found in subjects with amyotrophic lateral sclerosis (ALS). Disrupted endocrine function could contribute to the progressive muscle loss and hypermetabolism seen in ALS. It is not possible to study all the elements of the GH-IGF-I axis in ALS patients. Consequently, it remains unclear whether dysfunctional GH secretion contributes to disease pathogenesis and why GH and IGF-I directed treatment strategies are ineffective in human ALS. The hSOD1(G93A) transgenic mouse model is useful for the detailed investigation of the pathogenesis of ALS. We report that symptomatic male hSOD1(G93A) transgenic mice exhibit a deficiency in GH secretion similar to that seen in human ALS. Further characterization of the GH-IGF-I axis in hSOD1(G93A) mice reveals central and peripheral abnormalities that are not found in wild-type age-matched controls. Specifically, we observe aberrant endogenous pulsatile GH secretion, reduced pituitary GH content, and decreased circulating levels of IGF-I, indicating global GH deficiency in hSOD1(G93A) mice. Furthermore, a reduction in the expression of the IGF-I receptor α-subunit in skeletal muscle and lumbar spinal cords of hSOD1(G93A) mice suggests impaired IGF-I signaling within these tissues. This is the first account of disrupted GH secretion in a transgenic mouse model of ALS. These observations are essential for the development of effective GH and IGF-I targeted therapies in ALS.

Complement C5a-C5aR1 signalling drives skeletal muscle macrophage recruitment in the hSOD1 G93A mouse model of amyotrophic lateral sclerosis

BackgroundThe terminal pathway of the innate immune complement system is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). Terminal complement activation leads to generation of C5a, which through its receptor, C5aR1, drives immune cell recruitment and activation. Importantly, genetic or pharmacological blockage of C5aR1 improves motor performance and reduces disease pathology in hSOD1G93A rodent models of ALS. In this study, we aimed to explore the potential mechanisms of C5aR1-mediated pathology in hSOD1G93A mice by examining their skeletal muscles.ResultsWe found elevated levels of C1qB, C4, fB, C3, C5a, and C5aR1 in tibialis anterior muscles of hSOD1G93A mice, which increased with disease progression. Macrophage cell numbers also progressively increased in hSOD1G93A muscles in line with disease progression. Immuno-localisation demonstrated that C5aR1 was expressed predominantly on macrophages within hSOD1G93A skeletal muscles. Notably, hSOD1G93A × C5aR1-/- mice showed markedly decreased numbers of infiltrating macrophages, along with reduced neuromuscular denervation and improved grip strength in hind limb skeletal muscles, when compared to hSOD1G93A mice.ConclusionThese results indicate that terminal complement activation and C5a production occur in skeletal muscle tissue of hSOD1G93A mice, and that C5a-C5aR1 signalling contributes to the recruitment of macrophages that may accelerate muscle denervation in these ALS mice.

Innate Immunity in ALS

Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig’s disease, is the most common form of motor neuron disease. It is a debilitating, late onset neurodegenerative disorder that is characterized by the progressive death of upper and ┙-motor neurons within the central nervous system (CNS) (Bruijn and Cleveland, 1996). This results in symptoms of muscle weakness and atrophy of skeletal muscles, leading to paralysis and eventual death due to failure of respiratory muscles (Cozzolino et al., 2008). ALS has a prevalence of approximately 1~2 per 100,000 worldwide with males being more susceptible than females (1.3 ~ 1.6: 1) (Strong, 2003, Woodruff et al., 2008b, Worms, 2001). The majority of ALS cases (~90%) are thought to be sporadic with unknown aetiology and no robust environmental risk factors, with the remaining 10% being familial ALS. Of this 10%, approximately 20% have been linked to dominant mis-sense point mutations in the Copper/Zinc superoxide dismutase 1 (SOD1) gene which results in a gain of unidentified deleterious properties (Rosen et al., 1993). The two aetiologies of ALS (i.e. sporadic and familial) are indistinguishable on the basis of their clinical and pathological features, including progressive muscle weakness, atrophy and spasticity, each of which reflects the degeneration and death of upper and ┙-motor neurons (Boillee et al., 2006). The mechanisms leading to ALS are still unclear but theories have suggested that glutamate excitoxicity, oxidative stress, protein aggregation, mitochondrial dysfunction, cytoskeletal abnormalities and neuro-inflammation may all play a role (Bruijn et al., 2004). The present chapter will review the role of innate immune system, in particular the complement system, during the disease progression of ALS. It will review evidence for an involvement of the innate immune Toll-like receptor (TLR) system and receptor for advanced glycosylation end products (RAGE) in ALS patients and animal models of ALS. It will also comprehensively evaluate the role of the innate immune complement cascade in this disease. Finally, the future therapeutic possibilities for ALS, aimed at targeting components of the innate immune system will be discussed. We provide compelling evidence for specific inhibitors of complement C5a receptors as novel treatment strategies for ALS.