| RESEARCH SUMMARY:
Areas of research include: (i) experimental approaches to
treatment of murine beta-glucuronidase deficiency mucopolysaccharidosis
(Sly syndrome), (ii) biochemical and molecular genetics of
human deficiencies of beta-glucuronidase and carbonic anhydrases,
and (iii) developing transgenic mice and mouse models of human
disease by targeted mutagenesis.
(i) Since the discovery of the human deficiency for beta-glucuronidase,
we've used cells from these patients as a model to delineate
the steps in lysosomal enzyme transport. These studies led
to the discovery of the mannose 6-phosphate receptor-mediated
pathway which cells normally use to direct enzymes to lysosomes
and of the mannose/fucosyl/N-acetylglucosaminyl receptor on
macrophages, the target for enzyme replacement in another
lysosomal storage disease called Gaucher disease. The subsequent
discoveries of the mouse and dog models of beta-glucuronidase
deficiency have provided opportunities to test experimental
therapies for lysosomal storage diseases including enzyme
replacement with recombinant enzyme, bone marrow transplantation,
and gene therapy. Current research focuses on enzyme engineering
for delivery of enzyme across the blood-brain barrier and
to bone.
(ii) Carbonic anhydrases. We became interested in carbonic
anhydrases after we identified carbonic anhydrase II deficiency
as the primary defect in the syndrome of osteopetrosis with
renal tubular acidosis and cerebral calcification. A variety
of biochemical, genetic, and molecular genetic studies have
been initiated to define the regulation of CA II gene expression
and the molecular basis of CA II deficiency. In addition,
the affected patients provided unique opportunities for clinical
research to define the role of CA II in bone, brain, kidney,
eye, and stomach. Additional carbonic anhydrases have been
discovered, the functions of which are still being identified.
These novel CAs are purified and characterized, and an effort
made to isolate each gene. To define the function of these
novel carbonic anhydrases, we produce mouse knockout models
of the respective CA and strive to identify human diseases
resulting from the enzyme deficiency. Examples include CA
IV, a membrane-anchored CA in lung, kidney, and brain, and
CA VA and CA VB, two mitochondrial CAs. CA IX and CA XII have
also been identified recently and found to be overexpressed
in certain cancers, suggesting that these membrane CAs play
some role in progression of tumors. Their role in oncogenesis
is still under study. Recently, we have begun to study protein
folding diseases because a signal sequence mutation in CA
IV has been identified in families with retinitis pigmentosa,
which appears to be due to an apoptosis-inducing signal sequence
mutation.
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