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Impairment of adenylyl cyclase signal transduction in mecobalamin-deficient rats
1Department of Pharmacology, School of Medicine, Sapporo Medical University, Japan.
Abstract:
This study examined alterations in the beta-adrenoceptor-G5-adenylyl cyclase system in cerebral cortex membranes from vitamin B12-deficient rats fed a diet lacking vitamin B12 (mecobalamin) for 15 weeks. Basal, 5(7)-guanylylimidodiphosphate (GppNHp)-, isoproterenol-, and forskolin-stimulated adenylyl cyclase activities were significantly reduced in mecobalamin-deficient rats compared with those in control rats. However, no significant differences were observed in the amount and function of G5- estimated by immunoblotting and guanine nucleotide photoaffinity labeling, respectively, or in the densities and the dissociation constants of beta-adrenoceptors, estimated by [125I] pindolol binding, between control and the deficient rats. These results indicate that vitamin B12 deficiency results in the impairment of the coupling among the beta-adrenoceptor, G5- and the catalytic subunit of adenylyl cyclase, and in dysfunction of the catalytic subunit of the enzyme, suggesting that vitamin B12 participates in the regulation of neuronal adenylyl cyclase signal transduction.
Insights
Vitamin B12 deficiency impairs neuronal adenylyl cyclase signaling by disrupting the beta-adrenoceptor-G5-adenylyl cyclase coupling and enzyme function. This highlights vitamin B12
Area of Science:
- Neuroscience
- Biochemistry
- Cellular Signaling
Background:
- The beta-adrenoceptor-G5-adenylyl cyclase system is crucial for neuronal signal transduction.
- Vitamin B12 (mecobalamin) is essential for various biological functions, but its role in neuronal signaling pathways is not fully understood.
Purpose of the Study:
- To investigate the impact of vitamin B12 deficiency on the beta-adrenoceptor-G5-adenylyl cyclase system in rat cerebral cortex.
- To determine if vitamin B12 deficiency affects the coupling efficiency or catalytic function within this signaling cascade.
Main Methods:
- Cerebral cortex membranes were prepared from rats fed a vitamin B12-deficient diet for 15 weeks and control rats.
- Adenylyl cyclase activity was measured under basal, G5-stimulated (GppNHp), beta-adrenoceptor-stimulated (isoproterenol), and forskolin-stimulated conditions.
- G5- protein levels and function were assessed by immunoblotting and photoaffinity labeling, respectively.
- Beta-adrenoceptor density and affinity were determined using [125I] pindolol binding assays.
Main Results:
- Significantly reduced basal, G5-stimulated, isoproterenol-stimulated, and forskolin-stimulated adenylyl cyclase activities were observed in vitamin B12-deficient rats.
- No significant differences were found in G5- protein levels or function between deficient and control groups.
- Beta-adrenoceptor densities and dissociation constants remained unchanged, indicating intact receptor function.
Conclusions:
- Vitamin B12 deficiency impairs the coupling between the beta-adrenoceptor, G5-, and the catalytic subunit of adenylyl cyclase.
- Vitamin B12 deficiency leads to dysfunction of the catalytic subunit of adenylyl cyclase.
- These findings suggest that vitamin B12 plays a critical role in regulating neuronal adenylyl cyclase signal transduction.