ALS-causing SOD1 mutants generate vascular changes prior to motor neuron degeneration

Abstract

We report here that amyotrophic lateral sclerosis-linked superoxide dismutase 1 (SOD1) mutants with different biochemical characteristics disrupted the blood-spinal cord barrier in mice by reducing the levels of the tight junction proteins ZO-1, occludin and claudin-5 between endothelial cells. This resulted in microhemorrhages with release of neurotoxic hemoglobin-derived products, reductions in microcirculation and hypoperfusion. SOD1 mutant-mediated endothelial damage accumulated before motor neuron degeneration and the neurovascular inflammatory response occurred, indicating that it was a central contributor to disease initiation.

Figure 1. Breakdown of the blood-spinal cord barrier with microhemorrhages in different SOD1 mutants presymptomatically

(a) Double immunostaining for IgG (green) and CNS endothelium (CD31, red) in the lumbar spinal cord of wild type mouse and 3.5 months old SOD1^G37R and 6.5 months old SOD1^G85R mutants. (b) Quantification of the IgG signal intensity in the lumbar spinal cord of different SOD1 mutants at varying ages compared to their respective controls and SOD1^WT mice. NC, negative controls (omission of IgG antibody). (c) The number of motor neurons in the lumbar cord of different SOD1 mutants at an early stage of the disease process and in SOD1^WT mice expressed as a percentage of total number of motor neurons in non-transgenic controls. (d) Hemosiderin extra-neuronal and neuronal deposition in the lumbar spinal cords in different SOD1 mutants, but not in SOD1^WT mice. (e) Quantification of hemosiderin deposits in the lumbar spinal cord of different SOD1 mutants, controls and SOD1^WT mice. (f–h) Quantitative RT-PCR analysis of mRNA transcripts for MCP-1, Cox-2 and Icam-1 in the lumbar spinal cord of SOD1^G93A mice and controls at different age. Values are means ± s.e.m., n = 3–6 mice per group. *P < 0.05 compared to SOD1^WT or non-transgenic mice. All procedures were according to the NIH guidelines and approved by the University of Rochester Committee on Animal Resources.

Figure 2. SOD1 toxicity to endothelium results in loss of tight junction proteins and reductions in microcirculation and blood flow

(a) Immunoblot analysis of human hSOD1, mouse mSOD1, ZO-1, occludin and claudin-5, and Glut-1 in spinal cord microvessels from 2 months old SOD1^G93A mice compared to controls. Graph - band density for test-proteins relative to β-actin. (b) Immunoblot analysis of ZO-1, occludin and claudin-5 in the spinal cord capillaries from 7, 3.5 and 6.5 months old C57BL/6, mice, SOD1^G37R and SOD1^G85R mutants, respectively, and 7 months old SOD1^WT mice. Graph - band density for test-proteins relative to β-actin. *P < 0.05, SOD1 mutants vs. controls or SOD1^WT mice. (c) Total capillary length in the anterior horn of the lumbar spinal cord in SOD1 mutants (mm CD31-positive structures per mm²). *P < 0.05, SOD1 mutants vs. age matched controls. (d–e) Transmission electron microscopy (TEM) in 3.5 and 6.5 months old SOD1^G37R and SOD1^G85R mutants, respectively, shows edema (asterisk) between the capillary wall and motor neurons. Collapsed capillary lumen in SOD1^G93A mice. E, endothelium; BM, basement membrane, MN, motor neuron. (e) TEM of B6SJL mouse shows normal neuronal-vascular contact and intact endothelium. (f) Blood flow through the spinal cord and frontal cortex in 8 weeks old SOD1^G93A mice compared to controls. (g) Hemoglobin (Hb) toxicity to N2a cells transduced with SOD1^G37R and SOD1^G85R mutants and SOD1^WT. ^#P < 0.05, SOD1^G37R or SOD1^G85R vs. SOD1^WT. Mean ± s.e.m. a–c and f, n = 3–5 mice per group. g, n = 4 experiments per group.