Possible involvement of nitric oxide in carbachol-induced activation of transglutaminase in rat superior cervical sympathetic ganglia

Tissue-transglutaminase in rat and human brain: light and electron immunocytochemical analysis and in situ hybridization study

Tissue-type transglutaminases constitute a family of enzymes having a dual role. They catalyze the post-translational modification of proteins and play a role in signal transduction pathways, several isoforms have been cloned in the brain. Many in vitro experiments and post-mortem studies have claimed that the enzyme plays a central role in the development of neurodegenerative disorders, especially in CAG-triplet diseases. In the present investigation, we conducted an immunocytochemical study using two different antibodies raised against tissue-type transglutaminase. To confirm the enzyme expression, non-radioactive in situ hybridization was performed on adjacent sections. The study was completed by analyzing the ultrastructural localization of the enzyme by electron microscopy. Tissue-type transglutaminase was widely expressed in both the human and rat brain. Many positive cells exhibiting neuronal features were found in the brain and cerebellum. There was a preferential expression in elements of pyramidal and extrapyramidal pathways with less expression in the somatosensory system. The mRNA detection confirmed the distribution of the enzyme. The ultrastructural approach revealed the presence of the enzyme in all neuronal compartments. Light and electron microscopy studies showed the ubiquitous nature of the enzyme and its putative role in functional as well as putative pathological processes.

Transglutaminase-catalyzed protein cross-linking in the molecular program of apoptosis and its relationship to neuronal processes

1. One type of transglutaminase is usually accumulated in various forms of naturally occurring cell death and apoptosis. The accumulated enzyme is activated during the death process, leading to the formation of cross-linked protein structures. Degradation of the cross-linked apoptotic bodies results in the elevation of the epsilon (gamma-glutamyl)lysine isodipeptide concentration in body fluids, which may provide a diagnostic tool to monitor the apoptosis rate in various tissues under normal and pathologic conditions. 2. Extensive protein cross-linking may be directly related to the act of killing in some cells. In others, the effect of protein cross-linking is palliative, preventing leakage of macromolecules and enhancing phagocytosis of the dead cells. 3. Tissue transglutaminase has been implicated in some physiologic functions of the nervous system. 4. The molecular machinery of apoptosis is present and easily evoked in neuronal cells. 5. Effector elements of the apoptosis process have been associated with the pathogenesis of neurologic disorders. Tissue transglutaminase, representing one of the effector elements of apoptosis, may be induced and activated in cells following ischemia. It may also participate in the formation of abnormal cell inclusions and A beta deposits in amyloid plaques.