Decreased astrocytic thrombospondin-1 secretion after chronic ammonia treatment reduces the level of synaptic proteins: in vitro and in vivo studies

Arumugam R. Jayakumar, Xiao Y. Tong, Kevin M. Curtis, Roberto Ruiz-Cordero, Nagarajarao Shamaladevi, Missa Abuzamel, Joshua Johnstone, Gabriel Gaidosh, Kakulavarapu V. Rama Rao, Michael D Norenberg

Research output: Contribution to journalArticle

29 Scopus citations

Abstract

Chronic hepatic encephalopathy (CHE) is a major complication in patients with severe liver disease. Elevated blood and brain ammonia levels have been implicated in its pathogenesis, and astrocytes are the principal neural cells involved in this disorder. Since defective synthesis and release of astrocytic factors have been shown to impair synaptic integrity in other neurological conditions, we examined whether thrombospondin-1 (TSP-1), an astrocytic factor involved in the maintenance of synaptic integrity, is also altered in CHE. Cultured astrocytes were exposed to ammonia (NH₄Cl, 0.5-2.5 mM) for 1-10 days, and TSP-1 content was measured in cell extracts and culture media. Astrocytes exposed to ammonia exhibited a reduction in intra- and extracellular TSP-1 levels. Exposure of cultured neurons to conditioned media from ammonia-treated astrocytes showed a decrease in synaptophysin, PSD95, and synaptotagmin levels. Conditioned media from TSP-1 over-expressing astrocytes that were treated with ammonia, when added to cultured neurons, reversed the decline in synaptic proteins. Recombinant TSP-1 similarly reversed the decrease in synaptic proteins. Metformin, an agent known to increase TSP-1 synthesis in other cell types, also reversed the ammonia-induced TSP-1 reduction. Likewise, we found a significant decline in TSP-1 level in cortical astrocytes, as well as a reduction in synaptophysin content in vivo in a rat model of CHE. These findings suggest that TSP-1 may represent an important therapeutic target for CHE. Defective release of astrocytic factors may impair synaptic integrity in chronic hepatic encephalopathy. We found a reduction in the release of the astrocytic matricellular proteins thrombospondin-1 (TSP-1) in ammonia-treated astrocytes; such reduction was associated with a decrease in synaptic proteins caused by conditioned media from ammonia-treated astrocytes. Exposure of neurons to CM from ammonia-treated astrocytes, in which TSP-1 is over-expressed, reversed (by approx 75%) the reduction in synaptic proteins. NF-kB = nuclear factor kappa B; PSD95 = post-synaptic density protein 95; ONS = oxidative/nitrative stress.

Original languageEnglish
Pages (from-to)333-347
Number of pages15
JournalJournal of Neurochemistry
Volume131
Issue number3
DOIs
StatePublished - Nov 1 2014

Keywords

  • ammonia
  • astrocytes
  • chronic hepatic encephalopathy
  • synaptic proteins
  • thrombospondin-1

ASJC Scopus subject areas

  • Medicine(all)

Fingerprint Dive into the research topics of 'Decreased astrocytic thrombospondin-1 secretion after chronic ammonia treatment reduces the level of synaptic proteins: in vitro and in vivo studies'. Together they form a unique fingerprint.

  • Cite this

    Jayakumar, A. R., Tong, X. Y., Curtis, K. M., Ruiz-Cordero, R., Shamaladevi, N., Abuzamel, M., Johnstone, J., Gaidosh, G., Rama Rao, K. V., & Norenberg, M. D. (2014). Decreased astrocytic thrombospondin-1 secretion after chronic ammonia treatment reduces the level of synaptic proteins: in vitro and in vivo studies. Journal of Neurochemistry, 131(3), 333-347. https://doi.org/10.1111/jnc.12810