- Proteins and Peptides
- Lysates and Cell Lines
By Yoskaly Lazo-Fernandez, PhD
The cell surface receptor CD95 (also known as Fas or APO-1) is the best-characterized member of the tumor necrosis factor (TNF) receptor superfamily1. Many receptors in this family, including CD95 are called Death Receptors because of their ability to induce apoptosis2. In cells expressing CD95, apoptosis is triggered by the binding of this receptor’s specific ligand, CD95L. This mechanism, which was originally discovered in the early nineties, allows CD95L-expressing T lymphocytes and natural killer cells to trigger apoptosis in their targets. For this reason, CD95 was initially considered as a mediator of cell death only3. However, some CD95 expressing cells are resistant to CD95L-mediated apoptosis indicating that the biological function of CD95 goes beyond cell death induction. In fact, in recent years, intensive research revealed that CD95 is an important mediator of non-apoptotic signals. As such, CD95 has been implicated in a variety of new biological processes including cancer cell invasion, neurite sprouting and cell proliferation. In general, these novel CD95 activities are mediated by activation of MAPK kinases like p38, JNK and ERK as well as transcription factors like NFkB2–5.
ERK1/ERK2 was detected in perfusion fixed frozen sections of rat brain (cortex) using 15 µg/mL Rabbit Anti-Human/Mouse/Rat Phospho-ERK1/ERK2 (ERK1 T202/Y204, ERK2 T185/Y187) Antigen Affinity-purified Polyclonal Antibody (Catalog # AF1018) overnight at 4 °C. Tissue was stained with the Anti-Rabbit HRP-DAB Cell & Tissue Staining Kit (brown; Catalog # CTS005) and counterstained with hematoxylin (blue). View our protocol for Chromogenic IHC Staining of Frozen Tissue Sections.
Some of the newly reported, apoptosis-independent effects of CD95 activation are clearly relevant for the function of the nervous system. For example, CD95 has been shown to mediate neurite growth and branching in vitro6. Also, adult mice with impaired expression of CD95 exhibited neuronal atrophy and numerous neurological symptoms in their behavior7. However, it was unclear if the neurite growth effects would also be induced in vivo, and if the neurological consequences of CD95 gene deletion were directly related to CD95’s activity rather than to autoimmune problems.
Recent work by the laboratory of Ana Martin-Villalba in Germany aimed at solving these questions. In their publication8, Si Chen et al. demonstrated that the activation of CD95 indeed regulates neuronal branching both in vitro and in vivo. These authors also uncovered cellular and molecular mechanisms involved in this response. An essential technique used in this project was the cell-specific modulation of the expression of CD95 and related proteins. The downregulation of CD95 in cortical neurons of the developing brain, both in the embryo and early after birth, lead to a marked reduction of dendrite total length (35%) and number of branching points (25%). Overexpression of CD95 in the same cells had the opposite effects.
Neuronal and vessel growth share common regulatory mechanisms, and since endothelial cells (EC) express CD95 while being resistant to apoptosis, the authors studied if CD95 is involved in vascular development in the brain. Their results indicated that CD95 stimulates developmental angiogenesis by promoting EC proliferation and branching. The source of the activation of CD95 was in a cell type derived from the immune system, the macrophages. In contrast to neurons or EC, CNS macrophages express high levels of CD95L in the developing brain. Specific deletion of CD95L in CNS macrophages lead to a similar reduction in dendrite or EC development plus neuronal morphological and functional impairment in vivo. Overall these results strongly suggest that CNS macrophages are important players in the regulation of neurovascular development through the non-apoptotic activation of CD95. This discovery provides a new potential strategy for the modulation of neuronal plasticity and angiogenesis in CNS developmental disorders.
Yoskaly Lazo Fernandez, PhD
Emory University, Department of Medicine/Renal Division
Dr. Lazo-Fernandez is interested in understanding the dietary factors that contribute to the development of hypertension and other chronic diseases.