An exploration of multiple paths leading to cell death
Pierre Golstein's team initially investigated mechanisms of cell death by studying the function of cytotoxic CD8 T lymphocytes, killer white blood cells that can eliminate potentially harmful cells (cells that are stressed, infected or cancerous). The team showed that cytotoxic T cells use a varied arsenal to deliver a signal leading to cell death, and contributed to the identification of the two main mechanisms at play, either Fas-based or perforin/granzyme-based. On the way, this team identified in particular two molecules, CTLA-4 and IL-17, now used immuno-therapeutically.
The team subsequently explored the mechanisms of two models of developmental cell death, mouse interdigital cell death and Dictyostelium stalk cell death. The latter will be discussed in more detail below.
"After studying how killer cells kill, I wanted to understand how the target cells were dying," he says simply, explaining his first scientific mutation. Thus, his interest in cell death has shifted to issues of development. "Cell death is central to the development and renewal of organisms," says Pierre Goldstein "this is a normal phenomenon, and even vital: "aged" potentially defective cells are replaced by new cells, without which our body is changed. Control of this balance between cell renewal and destruction is an absolutely amazing phenomenon!"
Initially, he chose to study cells in the interdigital spaces of the mouse embryo, cells whose disappearance led to the individualization of the fingers. He then demonstrated that this scenario may involve two distinct types of cell death, apoptosis or necrosis.
Pierre Golstein recounts his discovery: "During the development of the legs of mice, the disappearance of interdigitating cells follows a process of apoptotic death, programmed in time and space. However, in mice in which a key gene for the process of apoptosis has been inactivated, Interdigital cells are still eliminated but this time by necrosis. To achieve the same ends, another mechanism of death has replaced the previous one. "
Self-cannibalism in an amoeba become "lab rat"
To study non-apoptotic cell death more easily, Pierre Golstein changed his experimental model. Rather than continue to study the mechanisms of cell death in mice, he now works on Dictyostelium discoideum, a unicellular organism that is genetically easy to manipulate and presents only non-apoptotic mechanisms of death.
What interests especially the team of Pierre Golstein is that in Dictyostelium autophagic cell death can be desmonstrated and includes autophagy (digestion by a cell of some of his own constituents), plus a second signal. This autophagic death of Dictyostelium can be induced in culture by deprivation of nutrients and by adding DIF1, a factor of differentiation that is such a second signal.
The team is now seeking to identify other molecules involved in this process of autophagic cell death, using random mutagenesis techniques. A vector, a "neutral" DNA sequence, is electroporated into Dictyostelium cells: it inserts randomly into the genome, possibly inactiivating a gene . Autophagic death is induced in the cell population of interest and the surviving cells are studied. "If a cell survives, it is may be because the vector has inactivated a gene that was necessary for its death," says Pierre Golstein. "Then, to know the identity of this gene, just extract the vector genome, with the adjacent DNA that is part of the gene of interest and is identifiable by sequencing."
With this strategy, Pierre Golstein and his team have found a number of molecules required for autophagic cell death. Today, the team is dedicated to the identification and study of other such molecules some of which may be conserved in evolution.