The central nervous system (CNS) is equipped with a variety of cell types, all of which are assigned particular roles during the development, maintenance, function and repair of neural tissue. One glial cell type, microglia, deserves particular attention, as its role in the healthy or injured CNS is incompletely understood. Evidence exists for both regenerative and degenerative functions of these glial cells during neuronal injury. This review integrates the current knowledge of the role of microglia in an adult-onset neurodegenerative disease, amyotrophic lateral sclerosis (ALS), and pays particular attention to the possible mechanisms of initiation and propagation of neuronal damage during disease onset and progression. Microglial cell properties, behavior and detected inflammatory reactions during the course of the disease are described. The neuroinflammatory changes that occur in a mouse model of ALS are summarized. The understanding of microglial function in the healthy and injured CNS could offer better diagnostic as well as therapeutic approaches for prevention, retardation, or repair of neural tissue degeneration.

Astrocytes are the most numerous cell type within the central nervous system (CNS) and perform a variety of tasks, from axon guidance and synaptic support, to the control of the blood brain barrier and blood flow. To perform these roles, there is a great variety of astrocytes. In this review, we summarize the function of astrocytes, in particular, their role in maintaining homeostasis at the synapse, regulating neuronal signaling, protecting neurons from oxidative damage, and determining the fate of endogenous neural precursors. The review also highlights recent developments indicating the role of astrocytes in motor neuron disease (MND), emphasizing their potential as therapeutic targets and agents in cell replacement therapy. The Cu-Zn superoxide dismutase (SOD1) gene that has been implicated in 20% of cases of familial MND must be expressed in the glial cells as well as motor neurons to produce the disease state in murine models of disease. Selectively reducing mutant SOD1 (mSOD1) in astrocytes does not affect disease onset but slows disease progression, whereas reducing mSOD1 in motor neurons delays disease onset and slows early disease but has less effect on life span. This suggests that glial cells represent potential therapeutic targets in MND. However, the lack of specific markers for astrocytes, their precursors, and sub-types means that our knowledge of astrocyte development/differentiation and response to injury lags far behind our understanding of function. Only by filling this knowledge gap can astrocytes be effectively targeted or replaced to successfully treat chronic CNS disorders such as MND.

During complement activation the C3 protein is cleaved, and C3 activation fragments are covalently fixed to tissues. Tissue-bound C3 fragments are a durable biomarker of tissue inflammation, and these fragments have been exploited as addressable binding ligands for targeted therapeutics and diagnostic agents. We have generated cross-reactive murine monoclonal antibodies against human and mouse C3d, the final C3 degradation fragment generated during complement activation. We developed 3 monoclonal antibodies (3d8b, 3d9a, and 3d29) that preferentially bind to the iC3b, C3dg, and C3d fragments in solution, but do not bind to intact C3 or C3b. The same 3 clones also bind to tissue-bound C3 activation fragments when injected systemically. Using mouse models of renal and ocular disease, we confirmed that, following systemic injection, the antibodies accumulated at sites of C3 fragment deposition within the glomerulus, the renal tubulointerstitium, and the posterior pole of the eye. To detect antibodies bound within the eye, we used optical imaging and observed accumulation of the antibodies within retinal lesions in a model of choroidal neovascularization (CNV). Our results demonstrate that imaging methods that use these antibodies may provide a sensitive means of detecting and monitoring complement activation-associated tissue inflammation.

One of the challenges of treating patients with glomerulonephritis (GN) is to accurately assess disease activity. We recently developed a magnetic resonance imaging (MRI)-based method of detecting glomerular C3, and hypothesized that this agent could be used to monitor the severity of GN. In the current study we used this imaging method to track the progression of renal disease in the MRL/lpr mouse model of lupus nephritis (LN). The targeting agent is comprised of superparamagnetic iron oxide (SPIO) nanoparticles conjugated to complement receptor type 2 (CR2-targeted SPIO). Glomerular C3b/iC3b/C3d deposition in progressively aging MRL/lpr and control mice was monitored with quantitative immunofluorescence or with CR2-targeted SPIO and T2-weighted MRI. Immunofluorescence showed that glomerular C3b/iC3b increased with disease activity. This finding was replicated with the T2-weighted MRI: T2-relaxation times decreased (as SPIO reduce T2-relaxation times) with disease activity in the cortex and medullas of MRL/lpr mice, but not of control mice. Our findings demonstrate that an MRI contrast agent targeted to glomerular C3b/iC3b/C3d can be used to non-invasively monitor disease activity in GN. Further, therapeutic complement-inhibitors have recently been used in patients with renal disease, and this method could identify patients likely to benefit from complement inhibition.

The inflammatory response in amyotrophic lateral sclerosis (ALS) is well documented but the underlying cellular mechanisms have not been fully elucidated. We report that microglia isolated from the mutant human superoxide dismutase 1 (SOD1) G93A transgenic mouse model of ALS have an increased response to the inflammatory stimulus, lipopolysaccharide. Cell surface area and F4/80 surface marker, both indicators of cell activation, are increased relative to transgenic wild-type human SOD1 microglia. Monocyte chemoattractant protein-1, known to be increased in ALS, is produced at three-fold higher levels by SOD1 G93A than by wild-type human SOD1 microglia, under activating conditions. This novel finding implicates ALS microglia as a source of the increased monocyte chemoattractant protein-1 levels detected in ALS patients and in the ALS mouse model.