Widespread CNS pathology in amyotrophic lateral sclerosis homozygous for the D90A SOD1 mutation.

Mutations in the gene encoding the ubiquitously expressed free radical scavenging enzyme superoxide dismutase-1 (SOD1) are found in 2-6% of amyotrophic lateral sclerosis patients. The most frequent SOD1 mutation worldwide is D90A. Amyotrophic lateral sclerosis caused by this mutation has some unusual features: the heredity is usually recessive, the phenotype is stereotypic with slowly evolving motor symptoms beginning in the legs and may also include sensory, autonomic, and urinary bladder involvement. Furthermore, the mutant protein resembles the wild type, with normal content and enzymatic activity in the central nervous system. Here, we report neuropathological findings in nine patients homozygous for the D90A mutation. All nine had numerous small granular inclusions immunoreactive for misfolded SOD1 in motor neurons and glial nuclei in the spinal cord and brainstem. In addition to degeneration of the corticospinal tracts, all patients had degeneration of the dorsal columns. We also found intense gliosis in circumscribed cortical areas of the frontal and temporal lobes and in the insula. In these areas and in adjacent white matter, there were SOD1 staining neuropil threads. A few SOD1-immunopositive cytoplasmic neuronal inclusions were observed in cortical areas, as were glial nuclear inclusions. As suggested by the symptoms and signs and earlier neurophysiological and imaging investigations, the histopathology in patients homozygous for the D90A SOD1 extends beyond the motor system to include cognitive and sensory cortical areas. However, even in the patients that had a symptomatic disease duration of more than 2 or 3 decades and lived into their 70s or 80s, there were no SOD1-inclusion pathology and no typical dysfunction (apart from the musculature) in non-nervous organs. Thus, only specific parts of the CNS seem to be vulnerable to toxicity provoked by homozygously expressed mutant SOD1.

Histological correlates of postmortem ultra-high-resolution single-section MRI in cortical cerebral microinfarcts.

The identification of cerebral microinfarctions with magnetic resonance imaging (MRI) and histological methods remains challenging in aging and dementia. Here, we matched pathological changes in the microvasculature of cortical cerebral microinfarcts to MRI signals using single 100 µm-thick histological sections scanned with ultra-high-resolution 11.7 T MRI. Histologically, microinfarcts were located in superficial or deep cortical layers or transcortically, compatible with the pattern of layer-specific arteriolar blood supply of the cerebral cortex. Contrary to acute microinfarcts, at chronic stages the core region of microinfarcts showed pallor with extracellular accumulation of lipofuscin and depletion of neurons, a dense meshwork of collagen 4-positive microvessels with numerous string vessels, CD68-positive macrophages and glial fibrillary acidic protein (GFAP)-positive astrocytes. In MRI scans, cortical microinfarcts at chronic stages, called chronic cortical microinfarcts here, gave hypointense signals in T1-weighted and hyperintense signals in T2-weighted images when thinning of the tissue and cavitation and/or prominent iron accumulation were present. Iron accumulation in chronic microinfarcts, histologically verified with Prussian blue staining, also produced strong hypointense T2*-weighted signals. In summary, the microinfarct core was occupied by a dense microvascular meshwork with string vessels, which was invaded by macrophages and astroglia and contained various degrees of iron accumulation. While postmortem ultra-high-resolution single-section imaging improved MRI-histological matching and the structural characterization of chronic cortical cerebral microinfarcts, miniscule microinfarcts without thinning or iron accumulation could not be detected with certainty in the MRI scans. Moreover, string vessels at the infarct margin indicate disturbances in the microcirculation in and around microinfarcts, which might be exploitable in the diagnostics of cortical cerebral microinfarcts with MRI in vivo.

Endothelial damage, vascular bagging and remodeling of the microvascular bed in human microangiopathy with deep white matter lesions.

White matter lesions (WMLs) are a common manifestation of small vessel disease (SVD) in the elderly population. They are associated with an enhanced risk of developing gait abnormalities, poor executive function, dementia, and stroke with high mortality. Hypoperfusion and the resulting endothelial damage are thought to contribute to the development of WMLs. The focus of the present study was the analysis of the microvascular bed in SVD patients with deep WMLs (DWMLs) by using double- and triple-label immunohistochemistry and immunofluorescence. Simultaneous visualization of collagen IV (COLL4)-positive membranes and the endothelial glycocalyx in thick sections allowed us to identify endothelial recession in different types of string vessels, and two new forms of small vessel/capillary pathology, which we called vascular bagging and ghost string vessels. Vascular bags were pouches and tubes that were attached to vessel walls and were formed by multiple layers of COLL4-positive membranes. Vascular bagging was most severe in the DWMLs of cases with pure SVD (no additional vascular brain injury, VBI). Quantification of vascular bagging, string vessels, and the density/size of CD68-positive cells further showed widespread pathological changes in the frontoparietal and/or temporal white matter in SVD, including pure SVD and SVD with VBI, as well as a significant effect of the covariate age. Plasma protein leakage into vascular bags and the white matter parenchyma pointed to endothelial damage and basement membrane permeability. Hypertrophic IBA1-positive microglial cells and CD68-positive macrophages were found in white matter areas covered with networks of ghost vessels in SVD, suggesting phagocytosis of remnants of string vessels. However, the overall vessel density was not altered in our SVD cohort, which might result from continuous replacement of vessels. Our findings support the view that SVD is a progressive and generalized disease process, in which endothelial damage and vascular bagging drive remodeling of the microvasculature.