The effect of dibutyryl cyclic AMP on the expression of actin isoforms in astroglia

dBcAMP Rescues the Neurons From Degeneration in Kainic Acid-Injured Hippocampus, Enhances Neurogenesis, Learning, and Memory

Dibutyryl cyclic adenosine monophosphate (dBcAMP) is a cell-permeable synthetic analog of cyclic adenosine monophosphate (cAMP). Although the elevation of cAMP levels was reported to promote the functional recovery in spinal cord injury, its role in neurogenesis or functional recovery after hippocampal injury is unknown. The objective of the study was to investigate the effects of dBcAMP on learning, memory, and hippocampal neurogenesis in the excitotoxically lesioned hippocampus. An excitotoxic lesion was induced in the hippocampi of 4-month-old male BALB/c mice by injecting 0.25 μg/μl into the lateral ventricles of both sides. The lesioned mice (L) were divided into L+dBcAMP and L+phosphate-buffered saline (PBS) groups. Sham surgery (S) was done by the injection of 1 μl of sterile saline into the lateral ventricles. The sham surgery mice were divided into S+dBcAMP and S+PBS groups. Mice in the L+dBcAMP and S+dBcAMP groups were treated with dBcAMP for 1 week (i.p., 50 mg/kg), whereas mice in the L+PBS and S+PBS groups were treated with PBS. The mice in all groups were subjected to water maze and passive avoidance tests at the end of the 4th week. Cresyl violet staining and NeuN and doublecortin immunostaining were done to analyze the morphology and neurogenesis. The water maze learning sessions did not show a significant difference in escape latency between the groups, suggesting an unimpaired learning ability of mice in all groups. The L+dBcAMP mice had significantly short entry latency and higher target quadrant time/distance traveled compared to the L+PBS group, suggesting better memory retention. The L+dBcAMP group had a significantly improved memory retention compared to the L+PBS mice during the passive avoidance test. Morphological studies showed significantly greater adult neurons and increased hippocampal neurogenesis in the hippocampus of mice in the L+dBcAMP group compared to those in the L+PBS group. There was no significant difference between the S+dBcAMP and S+PBS groups in the water maze/passive avoidance tests and the number of neurons. In conclusion, dBcAMP protects the hippocampal neuron from degeneration and enhances hippocampal neurogenesis, learning, and memory.

Dibutyryl Cyclic Adenosine Monophosphate Rescues the Neurons From Degeneration in Stab Wound and Excitotoxic Injury Models

Dibutyryl cyclic adenosine monophosphate (dBcAMP), a cell-permeable synthetic analog of cAMP, has been shown to induce astrogliosis in culture. However, the exact mechanism underlying how dBcAMP exerts its function in situ is not clear. The objective of this study was to examine the effects of dBcAMP on astrogliosis and survival of neurons in stab wound and kainic acid models of brain injury. Stab wound was done in cerebral cortex of BALB/c male mice. Kainic acid lesion was induced in hippocampus by injecting 1μl kainic acid into the lateral ventricle. Animals in both models of injury were divided into L+dBcAMP and L+PBS groups and treated with dBcAMP or PBS for 3, 5, and 7 days respectively. The brain sections were stained for Cresyl violet and Fluro jade-B to assess the degenerating neurons. Immunostaining for GFAP and Iba-1 was done for assessing the astrogliosis and microglial response respectively. Expression of GFAP and BDNF levels in the tissue were estimated by Western blotting and ELISA respectively. The results showed a gradual increase in the number of both astrocytes and microglia in both injuries with a significant increase in dBcAMP-treated groups. The number of degenerating neurons significantly decreased in dBcAMP treated groups. In addition, it was found that dBcAMP stimulated the expression of GFAP and BDNF in both stab wound and kainic acid injuries. Treatment with BDNF receptor inhibitor AZ-23, showed an increase in the degenerating neurons suggesting the role of BDNF in neuroprotection. This study indicates that dBcAMP protects neurons from degeneration by enhancing the production of BDNF and may be considered for use as therapeutic agent for treatment of brain injuries.

Effect of interleukin-1β on the expression of actin isoforms in cultured mouse astroglia

Cytokines are soluble mediators that are thought to act as communication signals between astroglia and neighboring neural cells. They are both released by, and act on, astroglia. It is hypothesized that it is this effect on astroglia that may be important in widespread phenomena including traumatic brain injury, inflammation, and scar formation. In this article, we examine the effect of mouse recombinant interleukin-1β (IL-1β) on the morphology, organization, and expression of glial fibrillary acidic protein (GFAP) and actin isoforms in cultured mouse astroglia. This study shows that the majority of the astroglia treated with IL-1β acquire long processes. Immunofluorescence staining shows that there are no remarkable changes in the organization of GFAP, F-actin, α-smooth muscle (α-sm) actin, and β-actin isoforms. In fluorescent microplate assay, the short-term treated astroglia (range, 1-2 days) show an increase in the intensity of GFAP and β-actin isoform over the level observed in untreated control, whereas no remarkable changes are observed in the intensity of α-sm actin isoform. In the case of long-term treatment (range, 4-8 days), the intensity of GFAP and α-sm actin isoform progressively decreases below the level of untreated control. In addition, the intensity of β-actin isoform increases above the control level. These results have been confirmed by immunoblotting experiments. The upregulation of β-actin isoform may be important in limiting the noxious effects of an inflammatory reaction. This gives credence to the hypothesis that it might be possible to modulate astroglial effects on neuronal inflammation and scar formation with appropriate therapies.

Alpha-smooth muscle actin (alpha-SMA) and nestin expression in reactive astrocytes in multiple sclerosis lesions: potential regulatory role of transforming growth factor-beta 1 (TGF-beta1)

AIMS

Rapid and extensive activation of astrocytes occurs subsequent to many forms of central nervous system (CNS) injury. Recent studies have revealed that the expression profile of reactive astrocytes comprises antigens present during astrocyte development. Elevated levels of the injury-related cytokine transforming growth factor-beta 1 (TGF-beta1) secreted by microglial cells and invading macrophages have been correlated with the reactive astrocyte phenotype and glial scar formation.

METHODS

In the present study, the expression profile of alpha-smooth muscle actin (alpha-SMA) and nestin, two cytoskeletal proteins expressed during astrocyte development, was studied in multiple sclerosis (MS) lesions. In addition, alpha-SMA and nestin organization and expression were analysed in rat primary astrocyte cultures in response to TGF-beta1.

RESULTS

In active lesions and in the hypercellular margin of chronic active MS lesions, immunostaining for alpha-SMA revealed a subpopulation of reactive astrocytes, whereas the majority of reactive astrocytes expressed nestin. alpha-SMA and nestin expressing reactive astrocytes were in close relationship with TGF-beta1 expressing macrophages or microglia. In addition, TGF-beta1 expression within alpha-SMA or nestin expressing astrocytes was also detected. Our in vitro experiments showed that TGF-beta1 regulated the organization and expression of alpha-SMA and nestin in astrocytes.

CONCLUSIONS

Reactive astrocytes in active MS lesions re-express alpha-SMA and nestin. We suggest that the in vivo re-expression might be under regulation of TGF-beta1. These results further clarify the regulation of astrocyte activity after CNS injury, which is important for the astroglial adaptation to pathological situations.