Methylmalonic acid reduces the in vitro phosphorylation of cytoskeletal proteins in the cerebral cortex of rats

The Regulation and Characterization of Mitochondrial-Derived Methylmalonic Acid in Mitochondrial Dysfunction and Oxidative Stress: From Basic Research to Clinical Practice

Methylmalonic acid (MMA) can act as a diagnosis of hereditary methylmalonic acidemia and assess the status of vitamin B12. Moreover, as a new potential biomarker, it has been widely reported to be associated with the progression and prognosis of chronic diseases such as cardiovascular events, renal insufficiency, cognitive impairment, and cancer. MMA accumulation may cause oxidative stress and impair mitochondrial function, disrupt cellular energy metabolism, and trigger cell death. This review primarily focuses on the mechanisms and epidemiology or progression in the clinical study on MMA.

In vitro phosphorylation of cytoskeletal proteins from cerebral cortex of rats

Procedures for the preparation of high- and low-salt Triton insoluble cytoskeletal fractions from rat brain suitable for studying in vitro phosphorylation by endogenous kinases and phosphatases are described. The high-salt Triton insoluble cytoskeletal fraction is enriched in neurofilament subunits (NF-H, NF-M and NF-L), vimentin and glial fibrillary acidic protein (GFAP), while the low-salt Triton insoluble cytoskeletal fraction contains detergent insoluble cytoskeletal elements such as intermediate filament subunits and tubulins. One of our approaches is to incubate cerebral cortex slices with [32P]orthophosphate before the cytoskeletal fraction extraction, which allows the in vitro phosphorylation of cytoskeletal constituents in an intact intracellular environment. On the other hand, we also incubate low- or high-salt cytoskeletal fractions previously prepared with [gamma(32)P]ATP. By doing so, we are able to study the direct effects of substances on the kinase and phosphatase activities associated with the cytoskeletal fraction. Moreover by using specific activators or inhibitors of protein kinases and phosphatases we can obtain more detailed information on the alterations provoked by these substances. These approaches are useful for the investigation of the neurotoxic effects of various drugs and metabolites affecting the cytoskeletal-associated phosphorylation system in the brain.

Methylmalonic and propionic acids increase the in vitro incorporation of 32P into cytoskeletal proteins from cerebral cortex of young rats through NMDA glutamate receptors

In this study we investigated the effects of methylmalonic acid (MMA) and propionic acid (PA) on the phosphorylation of cytoskeletal proteins of cerebral cortex of rats. Slices of tissue were incubated with 32P-orthophosphate in the presence or absence of glutamate, MMA, PA and ionotropic or metabotropic glutamate receptor agonists. The cytoskeletal fraction was isolated and the radioactivity incorporated into the cytoskeletal proteins was measured. Results demonstrated that the acids, glutamate and NMDA increased the phosphorylation of the proteins studied. However, this effect was not observed for non-NMDA ionotropic agonists or metabotropic agonists. Experiments using glutamate receptor antagonists confirmed that MMA and PA at the same concentrations as found in tissues from propionic or methylmalonic acidemic children increase the phosphorylation of cytoskeletal proteins, possibly via NMDA glutamate receptors. Therefore, it is feasible that these findings may be related to the neurological dysfunction characteristic of these disorders.

Effects of neonatal cerebral hypoxia-ischemia on the in vitro phosphorylation of synapsin 1 in rat synaptosomes

Synapsins are phosphoproteins related to the anchorage of synaptic vesicles to the actin skeleton. Hypoxia-ischemia causes an increased calcium influx into neurons through ionic channels gated by activation of glutamate receptors. In this work seven-day-old Wistar rats were submitted to hypoxia-ischemia and sacrificed after 21 hours, 7, 30, or 90 days. Synaptosomal fractions were obtained by Percoll gradients and incubated with 32P (10 microCi/g). Proteins were analysed by SDS-PAGE and radioactivity incorporated into synapsin 1 was counted by liquid scintillation. Twenty-one hours after hypoxia-ischemia we observed a reduction on the in vitro phosphorylation of synapsin 1, mainly due to hypoxia, rather than to ischemia; this effect was reversed at day 7 after the insult. There was another decrease in phosphorylation 30 days after the event interpreted as a late effect of hypoxia-ischemia. No changes were observed at day 90. Our results suggest that decreased phosphorylation of synapsin 1 could be related to neuronal death that follows hypoxia-ischemia.

Effects of acute and chronic administration of methylmalonic and propionic acids on the in vitro incorporation of 32P into cytoskeletal proteins from cerebral cortex of young rats

We studied the effects of acute and chronic administration of methylmalonic (MMA) and propionic (PA) acids on the in vitro incorporation of 32P into neurofilament subunits (NF-M and NF-L), alpha and beta tubulins, from cerebral cortex of rats. In the chronic treatment, drugs were administered subcutaneously from day 6-17 post-partum (MMA 0.76-0.89 micromol/g body weight and PA 0.93 micromol/g body weight). In the acute treatment MMA and PA were injected (MMA 3.78 micromol/g body weight and PA 3.90 micromol/g body weight). Control animals received saline in the same volumes. The Triton-insoluble cytoskeletal fraction of control in treated animals was isolated and incubated with 32P-ATP. Our results demonstrate that both drugs were able to inhibit 32P in vitro incorporation into neurofilaments and tubulins. The acute administration of MMA decreased the in vitro 32P incorporation into NF-L and alpha-tubulin subunit, whereas PA administration decreased the 32P in vitro incorporation into NF-M, NF-L, and tubulins. On the other hand, chronic MMA administration induced a decreased 32P in vitro incorporation into NF-M, while chronic treatment with propionate decreased the in vitro phosphorylation of NF-M and alpha-tubulin. This study provides consistent evidence that a decreased phosphorylation of cytoskeletal proteins is induced by MMA and PA metabolites which accumulate in methylmalonic and propionic acidemias respectively. Therefore, it is possible that an altered brain cytoskeletal metabolism could be related with the structural alterations of CNS observed in these disorders.