Identification of osmosensitive and ammonia-regulated genes in rat astrocytes by Northern blotting and differential display reverse transcriptase-polymerase chain reaction

Background/Aims: The hepatic encephalopathy (HE) is in part the result of astrocyte swelling with alterations of glial function. Detoxification of ammonia may be one mechanism by which astrocyte swelling is triggered in HE. Methods: The differential display polymerase chain reaction (DDRT-PCR) and Northern blot analysis were used for study the functional consequence of cell volume changes and ammonia on gene expression in primary rat astrocytes. Results: Differentially expressed cDNA products were identified with about 92% homology to genes coding for mouse proline rich protein expressed in brain (PRTB), rat clusterin, elongin, and human Kelch motif containing protein. As shown by Northern blot analysis, PRTB and clusterin mRNA levels were upregulated by 19–64% after 4–8 h by both ammonia and hypoosmolarity. Elongin mRNA expression increased by 97% in response to ammonia but slightly by hypoosmolarity. Further, hypoosmotic exposure for 1–24 hours but not ammonia led to an increase of 80% in KMCP mRNA levels. Conclusions: The identification of these genes offers the opportunity to identify unrecognized molecular mechanisms of HE. The finding that several genes are induced by both, hypoosmolarity and ammonia, supports the view that astrocyte swelling is a major, but not the only pathogenetic event in HE.