Role of porphyrin sequestration in the biogenesis of iron-laden astrocytic inclusions in primary culture.
Astrocytes in subcortical regions of the mammalian brain progressively accumulate iron-rich, autofluorecent cytoplasmic inclusions as a function of aging. Cysteamine (CSH) accelerates the appearance of this senescent glial phenotype in situ and in primary rat astroglial cultures. Porphyrins have been implicated as the source of orange-red autofluorescence in these glial inclusions. Yet, CSH has been shown to suppress porphyrin-heme biosynthesis in cultured astroglia. To determine whether porphyrin biosynthesis or sequestration participates in the biogenesis of these glial inclusions, the porphyrin precursor, (3)H-delta-aminolevulinic acid ((3)H-ALA) was administered to CSH-exposed and control rat astroglial cultures followed by light and electron microscopic autoradiography. Control cultures exhibited faint orange-red autofluorescence, intense (3)H-ALA labeling, numerous normal mitochondria and few cytoplasmic inclusions. In these cells, (3)H-ALA labeling largely occurred over normal mitochondria. The CSH-treated astroglia exhibited diminished (3)H-ALA labeling and contained numerous orange-red autofluorescent inclusions. The latter manifested internal compartments delimited by double membranes characteristic of damaged mitochondria. The complement of normal mitochondria in the CSH-exposed cells was markedly reduced. In the CSH-treated cells, (3)H-ALA labeling predominated over the large multi-compartmental inclusions. CSH attenuates de novo porphyrin-heme biosynthesis in astroglia but may induce punctate orange-red autofluorescence in the cytoplasm of these cells by promoting large numbers of damaged, porphyrin-containing mitochondria to form tight aggregates within the nascent gliosomes.
Schipper
H M
HM
Bloomfield Center for Research in Aging, Lady Davis Institute, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada. hyman.schipper@mcgill.ca
Small
L
L
Wang
X
X
Brawer
J R
JR
D000622:Aminolevulinic Acid / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000378:metabolism* / Q000648:ultrastructure; D001345:Autoradiography; D002478:Cells, Cultured; D003543:Cysteamine / Q000494:pharmacology*; D005453:Fluorescence; D002479:Inclusion Bodies / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008854:Microscopy, Electron; D017319:Photosensitizing Agents / Q000378:metabolism; D011166:Porphyrins / Q000378:metabolism*; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D017319:Photosensitizing Agents; D011166:Porphyrins; D011837:Radiation-Protective Agents; D003543:Cysteamine; D000622:Aminolevulinic Acid; D007501:Iron