Integrative neuroscience approach to neuropsychiatric lupus

Abstract

We present a succinct review of our approach to study the interactions between the DNA-reactive antibodies that cross-react with the GluN2A and GluN2B subunits of the N-methyl-D-aspartate receptor, denoted DNRABs, and their brain targets in subjects with neuropsychiatric systemic lupus erythematosus (NPSLE). We have analyzed the DNRAB-based brain symptomatology in mouse models of NPSLE by using an integrative neuroscience approach, which includes behavioral assessment coupled with electrophysiological studies of neural networks and synaptic connections in target brain regions, such as the CA1 region of the hippocampus. Our results suggest a framework for understanding the interactions between immune factors and neural networks.

Keywords: Brain autoimmunity; Cognition; Hippocampus; Mouse; NMDAR.

Fig. 1

Analysis of the effects of DNRABs at different levels of neural organization. a The graphs show DNRAB+ mice assessed in the clock maze, a test for spatial cognition [42]. For this task, the apparatus is a circular base platform (diameter, 85 cm) attached to a waterproof clear wall (30 cm high). Cold water (20 °C) is added to a depth of 2 cm. The perimeter wall is pierced by 12 holes, 4 cm in diameter, arranged equidistantly around the circumference so that they are 23 cm apart, like the 12 h on a clock face. The lower edge of each hole is 3 cm above the maze floor, that is, at mouse head level. Eleven of these tubes are sealed with black plugs, flush with the internal pool wall surface; one is open and leads to an escape pipe, which is 4 cm in diameter, made of black flexible plastic. Thus, from within the clock maze, the true exit looks similar to the decoys, even to the human eye. The pool is surrounded by distal unmoving cues, which are illuminated by focal white lights within a darkened testing room. The task consists in escaping into the open tube and connected pipe; the pipe is then removed and the mouse is transported to the nearby home cage. On the first day, the mice are trained to the same exit for four trials, while on the next day a different exit is used. Left, this group (n = 10) has circulating DNRABs that do not enter the brain and shows normal acquisition. Right, this group (n =10) is tested 4 weeks post-LPS (which allows DNRAB entry into the hippocampus) and shows significantly longer latency to find a second exit (P < 0.01, ANOVA for trials 5–8), a deficit in spatial flexibility. b Left, side view of the brain with the hippocampus highlighted in yellow. Right, neural recordings in freely moving animals show that DNRAB+ mice exhibit larger place fields after DNRABs enter this brain region. For these experiments, mice (n = 8) are implanted with multielectrode arrays (4 tetrodes), directed to dorsal CA1 (coordinates of −2.0 mm AP, +1.6 mm ML from bregma) [–85]. Neural activity is recorded with a unitary gain headstage preamplifier (HS-18; Neuralynx Bozeman, MT) that is connected to a programmable amplifier (Lynx-8, Neuralynx) linked to Cheetah-32 software (Neuralynx), which acquires single units at a sampling rate of 30 kHz (band-pass filter, 600–6 kHz). The headstage also includes two LEDs that are used for tracking the animal’s position at 30 frames per second, which is accomplished by linking an infrared-sensitive camera, mounted above the chamber, to the video input of the Cheetah software. Three days post-surgery, the implanted mice are placed in the behavioral arena over a period of 3–5 days. The figure shows representative firing rate maps, recorded 2 weeks pre-LPS and 4 weeks post-LPS, during 10-min sessions in an arena (viewed from the top, 40 cm on the side). Color scale indicates frequency (Hz, spikes per second), in which red corresponds to the peak firing rate and blue to null firing. The size of the place field is indicated below the arena. c Left, cartoon of the NMDAR showing the binding sites for glutamate and other ligands, as well as the DWEYS consensus sequence. Right, studies in ex vivo hippocampal slices reveal that application of DNRABs significantly enhances the size of the extracellularly recorded NMDAR-mediated synaptic potentials. d–e At high titer of DNRABs (>100 μg per ml), hippocampal pyramidal neurons undergo MPT pore opening (d, detected as loss of green fluorescence in the right panel; the blue color represents staining of cell bodies, 100 μm on the side), and apoptosis (e, detected as brown staining by TUNEL assay, especially noticeable in the right panel inset)