Molecular signaling in regional rodent astrocytic susceptibility to 1,3-dinitrobenzene.

Abstract

1,3-Dinitrobenzene (DNB) produces edematous, glio-vascular lesions that are initially confined to energy-demanding brainstem nuclei. Selective vulnerability of brainstem astrocytes to DNB is mediated by a ten-fold lower threshold for opening of the mitochondrial permeability transition pore (mtPTP). BCL-XL, BAX and BCL-2 are members of the BCL-2 protein family known to regulate both apoptotic and necrotic cell death signaling at the mtPTP. The levels at which these proteins are expressed relative to one another, where in the cell they are located and whether or not they are post-translational modified contributes greatly to the balance in active agonistic to active antagonistic BCL-2 proteins, and this critical balance has been hypothesized to dictate regional astrocytec susceptibility to DNB. Data acquired in this thesis show no evidence of treatment-related alterations in BCL-XL, BAX or BCL-2 protein expression in rat or mouse brainstem (sensitive) or cortical (non-sensitive) tissue homogenates, the subcellular location of BAX in brainstem or cortical homogenates acquired from either species, or the phosphorylation status of BCL-XL in primary rat brainstem or cortical astrocytes. However, moderate increases in BCL-XL protein levels are observed only in DNB-treated primary rat cortical astrocytes. These region-specific increases shift the constitutive balance in expression of antagonistic to agonistic BCL-2 proteins from a ratio which favors BAX to one in which BCL-XL and BAX are fairly comparably expressed in cortical astrocytes, while the BAX-favoring balance in expression is maintained in brainstem astrocytes. Additional investigations demonstrate that overexpression of BCL-XL minimizes DNB-induced inhibition of succinate dehydrogenase (complex II) and increases significantly the dose of DNB required to induce MPT onset in primary brainstem and cortical astrocytes. These data confirm that the observed modest enhancement of BCL-XL protein levels limited to non-sensitive cortical astrocytes is sufficient to explain differential regional sensitivity to DNB-induced mitochondrial dysfunction and may be adequate to account for the unique susceptibility of brainstem astrocytes to DNB.