BONE MARROW TRANSPLANTATION IN NEURONAL STORAGE DISEASES

Project: Research project

Project Details

Description

Neuronal storage diseases are inborn errors of metabolism that result
from deficient activity of lysosomal hydrolases. The resulting
catabolic deficiency leads to an accumulation of undergraded substrates
in the digestive-vacuolar (lysosomal) apparatus of cells, and to an
expanding cascade of events that eventually compromises cell function.
Although individuals with these diseases often appear normal at birth,
neurodegenerative changes inevitable ensue. Psychomotor deficiencies
can be severe and may include mental retardation, motor system
dysfunction, sensory deficits, and seizures. Although intracellular
storage in non-neuropathic forms of lysosomal disorders has been
successfully ameliorated by bone marrow transplantation (BMT), the
application of BMT to storage diseases with neuronal involvement (e.g,
Hurler's disease) has been highly controversial. Working with an
inherited model of lysosomal alpha-D-mannosidase deficiency (alpha-
mannosidosis), we have unequivocally demonstrated not only that this
enzyme increases in activity in the CNS post-BMT, but that intraneuronal
storage is reversed and/or prevented. Most importantly, we have used an
indigogenic histochemical substrate to demonstrate that acidic alpha-
mannosidase is present with neurons and other cells of the CNS. This
remarkable finding has established the principle of therapeutic efficacy
for BMT in neuronal storage diseases and has led us to evaluate treatment
in a different type of storage disorder - GM2 gangliosidosis - using an
animal model of BETA-D-N-acetylhexosaminidase deficiency. Our
preliminary studies reveal a dramatically different result: In spite of
significant elevations of Beta-hexosaminidase activity in brain (30% of
normal), substrate reduction was not evident and histochemical staining
demonstrated that the enzyme was limited to brain microglia/macrophages.
We believe that differences in efficacy in the above models can be
exploited in the testing of hypotheses on the mechanism underlying
successful treatment. The most commonly stated rationale for use of BMT
in children is that donor blood monocytes enter brain, differentiate as
microglia, and provide a source of enzyme to enzyme deficient brain
cells. Alternative hypotheses include uptake of 'free' enzyme derived
from the circulation, and 'metabolic filtration' which depends on
substrate diffusion out of diseased cells with uptake and degradation by
donor cells. None of these hypotheses is proven and we propose to test
them using multidisciplinary in vivo and in vitro studies. Transplants
will be carried out in out models at different ages to assess the
importance of early treatment, and the dynamics of monocyte invasion of
brain in the early weeks post-BMT will be critically examined.
Therapeutic effectiveness for these studies will be assessed by clinical,
biochemical, histochemical, immunocytochemical and histopathologic
criteria. Using cell culture, we will determine whether putative bone
marrow-derived cells from normal animals have the capacity to transfer
lysosomal enzyme to brain cells from affected animals and whether
differential secretion or uptake of alpha-mannosidase and Beta-
hexosaminidase occurs. Alternative mechanisms leading to substrate
depletion also will be tested. Taken together, these multidisciplinary
studies will provide valuable insight into mechanism(s) underlying
metabolic correction in neurons following BMT and into pragmatic issues
related to BMT as therapy for neuronal storage diseases in children.
StatusFinished
Effective start/end date8/8/947/31/95

Funding

  • National Institute of Neurological Disorders and Stroke

ASJC

  • Neurology
  • Cellular and Molecular Neuroscience
  • Molecular Medicine
  • Developmental Neuroscience
  • Pharmacology