Abstract 2028
Activation of NMDA receptors, influx of Ca2+, and generation of free radicals are proposed mechanisms of neuronal damage in HIV-1 infection of the CNS (Lipton SL. Brain Pathol 6:507-517, 1996). Calbindin-D28k is an intracellular calcium-binding protein that provides the cell with Ca2+ buffering capability. It is widely expressed in Purkinje cells (PCs) of the developing and mature human cerebellar cortex (Katsetos CD, et al. J Neuropathol Exp Neurol 52:655-666, 1993). We hypothesize that HIV-1 CNS infection may hinder the ability of PCs to produce, or adequately maintain, calbindin-D28k resulting in increased neuronal vulnerability to intracellular [Ca2+]. We studied by immunohistochemistry, using a mAb against calbindin-D28k (clone CL-300, Sigma) formalin-fixed, paraffin-embedded autopsy cerebellar sections from ten children with AIDS (age range, 2 months-11 years), and four children (age range, 2 months-5 years) without evidence of neurologic disease (controls). Horizontal and parasagittal sections of the vermis and cerebellar hemispheres were analyzed and 576 to 1553 (median: 1059)(controls) and 416 to 779 (median, 566)(AIDS) PCs were counted per each case. Axonal staining of subcortical (folial) and deep cerebellar white matter was evaluated and rated as present (score=1) or absent (score=0). Compared to controls (mean of + PCs: 94%, SD: 7%), a significant, predominantly somatodendritic, reduction of calbindin-D28k staining in PCs is detected in 9/10 children with AIDS (mean of +PCs: 64%, SD: 7%) (p= 0.036 vs controls). Alterations of calbindin-D28k immunoreactivity in PCs include, lack of somatic staining, weak or floccular/punctuate somatic localization, and zonal redistribution toward the periphery of the cell body. A solely nuclear compartmentalization is detected in a small number of PCs of children with AIDS. This pattern is not detected in controls. Absence or paucity of staining in the Purkinje apical dendrites in the molecular layer is present variously in 9/10 AIDS cases and has a patchy/segmental distribution (p<0.001 vs controls). Overall, there is sparing of calbindin-D28k-positive axons in the cerebellar white matter. A reduction in calbindin-D28k immunoreactivity together with altered patterns of cellular localization indicate a disturbance in the Ca2+ reducing and neuroprotective mechanisms of PCs in children with AIDS.
