METHYLMALONIC ACID REDUCES THE IN-VITRO PHOSPHORYLATION OF CYTOSKELETAL PROTEINS IN THE CEREBRAL-CORTEX OF RATS

The present work was undertaken to determine the action of methylmalon ic acid (MMA), a metabolite, which accumulates in high amounts in meth ylmalonic acidemia, on the endogenous phosphorylating system associate d with the cytoskeletal fraction proteins of cerebral cortex of young rats. We demonstrated that pre-treatment of cerebral cortex slices of young rats with 2.5 mM buffered methylmalonic acid (MMA) is effective in decreasing in vitro incorporation of [P-32]ATP into neurofilament s ubunits (NF-M and NF-L) and alpha- and beta-tubulins. Based on the fac t that this system contains cAMP-dependent protein kinase (PKA), Ca2+/ calmodulin-dependent protein kinase II (CaMKII) and protein phosphatas e 1 (PP1), we first tested the effect of MMA on the kinase activities by using the specific activators cAMP and Ca2+/calmodulin or the inhib itors PKAI or KN-93 for PKA and CaMKII, respectively. We observed that MMA totally inhibited the stimulatory effect of cAMP and interfered w ith the inhibitory effect of PKAI. In addition, the metabolite partial ly prevented the stimulatory effect of Ca2+/calmodulin and interfered with the effect of KN-93. Furthermore, in vitro dephosphorylation of n eurofilament subunits and tubulins was totally inhibited in brain slic es pre-treated with MMA. Taken together, these results suggest that MM A, at the same concentrations found in tissues of methylmalonic acidem ic children, inhibits the in vitro activities of PKA, CaMKII and PP1 a ssociated with the cytoskeletal fraction of the cerebral cortex of rat s, a fact that may be involved with the pathogenesis of the neurologic al dysfunction characteristic of methylmalonic acidemia. (C) 1997 Else vier Science B.V.