Cyclic AMP-induced shape changes of astrocytes are accompanied by rapid depolymerization of actin

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Astrocytes exhibit dynamic shape changes in response to various stimuli.
• Intracellular cyclic AMP (cAMP) is a key second messenger involved in cellular signaling pathways.

Purpose of the Study:

• To investigate the short-term cytoskeletal rearrangements in astrocytes during shape conversion induced by increased intracellular cAMP.
• To elucidate the roles of actin and microtubules in cAMP-mediated astrocyte morphology changes.

Main Methods:

• Primary astrocyte cultures from neonatal rat forebrain were treated with dibutyryl cAMP (dBcAMP).
• Cell morphology was assessed, and cytoskeletal components (actin, vimentin, tubulin, GFAP) were analyzed.
• Changes in actin localization and stress fiber integrity were visualized using rhodamine-phalloidin.
• The effects of colchicine and taxol on dBcAMP-induced shape changes were examined.

Main Results:

• Dibutyryl cAMP rapidly induced significant astrocyte shape changes, characterized by cytoplasmic contraction and process extension.
• No changes in total cellular levels of GFAP, vimentin, tubulin, or actin were observed.
• A significant shift of actin from an insoluble to a soluble pool occurred, correlating with stress fiber loss.
• Microtubule integrity was found to be necessary for dBcAMP-induced shape changes, while taxol pretreatment could overcome colchicine inhibition.

Conclusions:

• Dibutyryl cAMP treatment leads to actin depolymerization in stress fibers, facilitating astrocyte contraction.
• An intact microtubule system appears essential for mediating the morphological transformation of astrocytes.
• Astrocyte adhesion sites, marked by vinculin, are lost during microfilament dissociation and shape change.