Iba-1-/CD68+ microglia are a prominent feature of age-associated deep subcortical white matter lesions

Abstract

Deep subcortical lesions (DSCL) of the brain, are present in ~60% of the ageing population, and are linked to cognitive decline and depression. DSCL are associated with demyelination, blood brain barrier (BBB) dysfunction, and microgliosis. Microglia are the main immune cell of the brain. Under physiological conditions microglia have a ramified morphology, and react to pathology with a change to a more rounded morphology as well as showing protein expression alterations. This study builds on previous characterisations of DSCL and radiologically ‘normal-appearing’ white matter (NAWM) by performing a detailed characterisation of a range of microglial markers in addition to markers of vascular integrity. The Cognitive Function and Ageing Study (CFAS) provided control white matter (WM), NAWM and DSCL human post mortem tissue for immunohistochemistry using microglial markers (Iba-1, CD68 and MHCII), a vascular basement membrane marker (collagen IV) and markers of BBB integrity (fibrinogen and aquaporin 4). The immunoreactive profile of CD68 increased in a stepwise manner from control WM to NAWM to DSCL. This correlated with a shift from small, ramified cells, to larger, more rounded microglia. While there was greater Iba-1 immunoreactivity in NAWM compared to controls, in DSCL, Iba-1 levels were reduced to control levels. A prominent feature of these DSCL was a population of Iba-1-/CD68+ microglia. There were increases in collagen IV, but no change in BBB integrity. Overall the study shows significant differences in the immunoreactive profile of microglial markers. Whether this is a cause or effect of lesion development remains to be elucidated. Identifying microglia subpopulations based on their morphology and molecular markers may ultimately help decipher their function and role in neurodegeneration. Furthermore, this study demonstrates that Iba-1 is not a pan-microglial marker, and that a combination of several microglial markers is required to fully characterise the microglial phenotype.

Oligodendrocyte pathology exceeds axonal pathology in white matter in human amyotrophic lateral sclerosis

“…Double-staining immunohistochemistry in ALS cases appeared to show a population of hypertrophic Iba1 − / NG2 + cells, which were considered to correspond to oligodendroglia. This conclusion should be treated with caution given evidence that some microglia are also negative for Iba1 [30]. Thus, the discrepancy with our study may be due to the differing antibodies used: MAP2+13 tends to target more mature oligodendrocyte precursor cells than NG2 and has less cross-reactivity with monocytes [28].…”

Demonstrating a reduced capacity for removal of fluid from cerebral white matter and hypoxia in areas of white matter hyperintensity associated with age and dementia

“…Our own results in post-mortem human cortical occipital sections demonstrate that there was no significant difference in the percentage area of collagen IV, laminin or fibronectin in CAA compared to age matched control sections [ 48 ]. However, collagen IV, a key glycoprotein component of the BM has been recently shown as increased in human WMH [ 49 ]. It may be that the hypoxic environment leads to an increase in laminin synthesis as a compensatory mechanism for the change in homeostasis of the brain, possibly leading to angiogenesis [ 50 ].…”

Up-regulation of pro-angiogenic pathways and induction of neovascularization by an acute retinal light damage

“…www.nature.com/scientificreports www.nature.com/scientificreports/ To prove more confidently the presence of vessels in the ONL, we also performed a double staining with IB4 and anti-Vwf (Fig. 6), which allows to exclude a microglial sub-population with IBA-1 − /CD68 + phenotype 41 . The two signals clearly co-localized in the photoreceptor layer (yellow arrows) confirming the presence of blood vessels.…”