Expression of terminin, a senescence-related cytoplasmic protein, in the aging rat brain

Differential response of mature TrkA/p75(NTR) expressing human and pig oligodendrocytes: aging, does it matter?

A differential morphological response of mature oligodendrocytes (OL) isolated from human and pig brains to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and to the nerve growth factor (NGF) was observed. In both cases, OL regenerate their processes; however, the rate and the extension of the process formation of human OL were behind that of pig OL. Presumably, the advanced age of the human tissue in these experiments might have contributed to this decrease in process formation, an effect that was already observed for rat OL [Yong et al. (1991) J Neurosci Res 29:87-99]. The less effectivity of NGF via TrkA, which was immunocytochemically shown in human OL, and of TPA via the protein kinase C (PKC) pathway, may have its common focus on the mitogen-activated protein kinase (MAPK) cascade. In this context, it was noted that only a few studies on aging of mature OL are available. It is conceivable that age-related changes in the properties of OL could be an important factor for their cellular responsiveness during longer lasting demyelinating diseases such as multiple sclerosis. Hence, this review would like to provide a basis for future investigations on the aging of mature OL. The data presently available suggest a preliminary classification of mature OL into three categories.

Ependymal development, proliferation, and functions: a review

A survey of the literature shows that proliferation of ependyma occurs largely during the embryonic and early postnatal periods of development in most species. Differentiation of these cells proceeds along particular regional and temporal gradients as does the expression of various cytoskeletal (vimentin, cytokeratins, glial fibrillary acidic protein) and secretory proteins (S-100). Turnover declines significantly postnatally, and only low levels of residual activity persist into adulthood under normal conditions. Although the reported response of ependyma to injury is somewhat equivocal, only limited regenerative capacity appears to exist and to varying degrees in different regions of the neuraxis. Proliferation has been most often observed in response to spinal cord injury. Indeed, the ependyma plays a significant role in the initiation and maintenance of the regenerative processes in the spinal cord of inframammalian vertebrates. In the human, however, ependyma appears never to regenerate at any age nor re-express cytoskeletal proteins characteristic of immature cells. The functions of ependyma including tanycytes, a specialized form of ependymal cell that persists into adulthood within circumscribed regions of the nervous system, are still largely speculative. Fetal unlike mature ependyma is believed to be secretory and is believed to play a role in neurogenesis, neuronal differentiation/axonal guidance, transport, and support. In the adult brain, mature ependyma is not merely an inert lining but may regulate the transport of ions, small molecules, and water between the cerebrospinal fluid and neuropil and serve an important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood.

Characterization of senescence- and apoptosis-dependent forms of terminin as derived from a precursor found in replicating and nonreplicating cells

Previously we have reported the production of a monoclonal antibody (Mab 1.2) which recognizes a cytoplasmic protein, terminin, in three different molecular weights: 90 (Tp90), 60 (Tp60), and 30 kDa (Tp30) forms. Further characterization shows that Tp90 is found in young growing and nongrowing quiescent fibroblasts, while Tp60 is found in permanently growth-arrested senescent fibroblasts and Tp30 in cells committed to undergo programmed cell death (apoptosis). In tissue, Tp90 is found in embryonic brain; later, in neonatal brain after terminal differentiation is completed, only Tp60 is found. Tp30 is found in crude liver fractions extracted without the protective action of protease inhibitors. In all these circumstances, Tp90 is mostly seen in the detergent-soluble fraction, while Tp60 and Tp30 are detergent-insoluble. We now report that in cultured fibroblasts, as well as in tissues such as brain and liver, Tp60 and Tp30 are derived from the Tp90 polypeptide, indicated by the fact that only the Tp90 species is identified by both immunoblotting and immunoprecipitation assays, when the cell or tissue extracts are prepared in the presence of protease inhibitors. Further evidence shows that immunoprecipitation of in vitro translation products from brain, liver, and cultured fibroblasts also present a single band of Tp90 polypeptide. Pulse-chase experiments show that during apoptosis, Tp90 is processed to Tp60, and eventually to Tp30. However, when the total protein extracts are fractionated, only Tp90 is found in the detergent-soluble fraction, with diminishing quantities during the time course of apoptosis, and Tp30, in contrast, is found as the only protein species in the insoluble fraction, with increasing quantity during the same time course. Newly processed Tp60 is not found in either of the fractions, reflecting its loss during the fractionation procedure. Limited one-dimensional peptide mapping of Tp90 yields three different bands at 30, 28, and 25 kDa, but only the one at 30 kDa is recognized by Mab 1.2. These results lead us to suggest that terminin protein is synthesized in the Tp90 form, and cleaved to lower molecular weight forms depends upon different physiologic conditions, with Tp60 processed in the terminally differentiated or senescent state and rapidly to Tp30 in apoptosis. Our findings further suggest that Tp90's processing to either Tp60 or Tp30 produces insoluble protein forms. Furthermore, the presence of Tp90 in nonapoptotic (either replicating or nonreplicating) cells may reflect the absence of necessary proteolytic action required for the execution of apoptosis. Future experiments will allow us to determine the nature of this proteolytic action, as well as whether this action is due to the autocatalytic action of Tp90 or by other endogenous proteases, and then to determine the significance of this biochemical action in cells.

The ependyma: a protective barrier between brain and cerebrospinal fluid

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.

Terminin (Tp 63/60), a novel cell senescence-related protein, is present in the aging human hippocampus

We have previously identified a cell senescence-related, detergent-insoluble cytoplasmic protein referred to as terminin, and have presented the development-dependent modification of terminin polypeptides in rat brain. In the present study, we characterize biochemically and immunocytochemically terminin expression in human hippocampus. By immunoblotting with a monoclonal antibody (mab 1.2) against terminin, we identified a 63 kDa polypeptide (Tp63) in the detergent-insoluble fraction of human brain proteins, which can be identified by either one- or two-dimensional electrophoresis. The 63 kDa protein in immunoprecipitates of human hippocampus was found to share a peptide pattern with the 60 kDa terminin (Tp60) previously found in rat brain, as demonstrated by in situ peptide mapping, suggesting that the human 63 kDa protein is a homologue of the rat Tp60. By immunocytochemistry, terminin immunoreactivity was demonstrated throughout the neuronal layers in the human hippocampus. The pyramidal cell layer in hippocampus proper and subiculum, as well as the granule cells in the dentate gyrus, gave rise to immunoreactivity for terminin. It was observed that in the cornu Ammonis, the highest terminin immunoreactivity was present in the pyramidal neurons of CA1. At the cellular level terminin was localized intraneuronally, as demonstrated by confocal microscopy of double staining with both mab 1.2 and an anti-neurofilament antibody. Taken together, the present study establishes that terminin is expressed in abundance in aging human CNS neurons.