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SERCA1 and Sarcolipin in Brody Disease
Each muscle contraction requires the entry of
Ca2+ into the muscle cytoplasm,
while relaxation requires removal of the activating
Ca2+, making
Ca2+ regulation of muscle one of
the most extensive activities in the human body. It is not surprising, therefore,
that proteins involved in
Ca2+ regulation, when mutated, can
lead to a variety of skeletal and cardiac muscle diseases that are related
to defects in Ca2+ regulation.
One
of these diseases is Brody disease (BD), an inherited disorder of skeletal
muscle function that is characterized by exercise-induced contracture brought
on by delayed relaxation. We studied three human BD families where the disease
is clearly autosomal recessive and found premature stop codons in the ATP2A1
gene, encoding SERCA1 (homozygous in two; compound heterozygous in the other),
leading to truncation and complete loss of SERCA1 function.
While these studies show that defects in ATP2A1 are a probable causal of
recessive forms of BD, they raise the interesting question of how humans
lacking SERCA1, which normally accounts for 99% of SERCA isoforms in fast-twitch
muscle, are able to function at all. We are creating an ATP2A1 knockout mouse
to provide material for determination of how abnormal
Ca2+ regulatory systems can be
compensated for in muscle disease.
Brody disease also occurs with autosomal dominant inheritance. We have shown
that ATP2A1 is not the causal gene in these cases. A current goal is to determine
the causal gene for autosomal dominant BD. We have investigated the possibility
that SLN might be mutated to become a stronger inhibitor of SERCA1 in these
families. We were, however, unable to find any mutations in the SLN gene
in several Brody families.
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Brody Disease Publications
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Odermatt, A., Becker, S., Khanna, V.K., Kurzydlowski, K.,
Leisner, E., Pette, D. and MacLennan, D.H. (1998) Sarcolipin regulates the
activity of SERCA1, the fast-twitch skeletal muscle sarcoplasmic reticulum
Ca2+ ATPase. Journal of Biological
Chemistry 273(in press)
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Structure-function analysis of the
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New York Acad. Sci. (in press)
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