NAD+ supplementation reverses the oxidative stress induced PARP1 signalling in D. Discoideum

Increased oxidative stress leads to cell death by inducing DNA damage, PARP activation and energy depletion in age related disorders which are a growing concern due to increased life expectancy. Indeed, cellular NAD+ levels, depletion of which is one of the consequences of overactive PARP, also decline with age. We previously showed rescue in oxidative stress induced paraptotic and necrotic cell death by PARP1 inhibition in D. discoideum. Inhibition of PARP1 activity prevented cellular depletion of its substrate NAD+. To understand the significance of NAD+ depletion in PARP1 mediated oxidative stress induced cell death, exogenous addition of NAD+ was done. Addition of NAD+ prevented PARP1 mediated oxidative stress induced cell death at low doses upto 10 mM NAD+, nevertheless led to an anticipated increase in PARP1 activity. NAD+ significantly prevented oxidative stress induced cell death in D. discoideum. Exogenous NAD+ averted depletion of cellular NAD+ and mitochondrial membrane potential changes that were triggered by oxidative stress, without getting affected by the elevated ROS levels. Altogether, this study ascertains that NAD+ replenishment overcomes cadmium or H2O2 induced cell death by preventing cellular energy collapse incited by PARP1 activation. Thus, our results explicitly demonstrate that PARP1 overactivation led NAD+ depletion but not PARP1 activity per se is of consequential significance in causing oxidative stress induced D. discoideum cell death. Moreover, NAD+ supplementation could be a beneficial approach in aging and age-related disorders mediated by PARP1

Staurosporine induced poly (ADP-ribose) polymerase independent cell death in Dictyostelium discoideum.

In the present study D. discoideum has been used as a model organism to understand the role of poly (ADP-ribose) polymerase (PARP) in caspase independent paraptotic cell death pathways. D. discoideum lacks caspases and Bcl-2 family proteins; nevertheless it has 9 potential genes for PARP. PARP has been known to get activated in various cell death associated diseases. In this study kinetics of cell death induced by staurosporine (STS), a bacterial alkaloid, was established to unravel the role of PARP. It was found that STS induced cell death in D. discoideum did not involve PARP activation, however it involved cathepsin D. Results indicated that an alternative mechanism may be existing in D. discoideum that lacks Bcl-2 family proteins for STS induced cell death that evades Bax involvement.

Signaling molecules involved in the transition of growth to development of Dictyostelium discoideum.

The social amoeba Dictyostelium discoideum, a powerful paradigm provides clear insights into the regulation of growth and development. In addition to possessing complex individual cellular functions like a unicellular eukaryote, D. discoideum cells face the challenge of multicellular development. D. discoideum undergoes a relatively simple differentiation process mainly by cAMP mediated pathway. Despite this relative simplicity, the regulatory signaling pathways are as complex as those seen in metazoan development. However, the introduction of restriction-enzyme-mediated integration (REMI) technique to produce developmental gene knockouts has provided novel insights into the discovery of signaling molecules and their role in D. discoideum development. Cell cycle phase is an important aspect for differentiation of D. discoideum, as cells must reach a specific stage to enter into developmental phase and specific cell cycle regulators are involved in arresting growth phase genes and inducing the developmental genes. In this review, we present an overview of the signaling molecules involved in the regulation of growth to differentiation transition (GDT), molecular mechanism of early developmental events leading to generation of cAMP signal and components of cAMP relay system that operate in this paradigm.