Apoptosis inducing factor: Cellular protective function in Dictyostelium discoideum

The neuroprotective effects of intermittent fasting on brain aging and neurodegenerative diseases via regulating mitochondrial function

Intermittent fasting (IF) has been studied for its effects on lifespan and the prevention or delay of age-related diseases upon the regulation of metabolic pathways. Mitochondria participate in key metabolic pathways and play important roles in maintaining intracellular signaling networks that modulate various cellular functions. Mitochondrial dysfunction has been described as an early feature of brain aging and neurodegeneration. Although IF has been shown to prevent brain aging and neurodegeneration, the mechanism is still unclear. This review focuses on the mechanisms by which IF improves mitochondrial function, which plays a central role in brain aging and neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. The cellular and molecular mechanisms of IF in brain aging and neurodegeneration involve activation of adaptive cellular stress responses and signaling- and transcriptional pathways, thereby enhancing mitochondrial function, by promoting energy metabolism and reducing oxidant production.

Calorie restriction potentiates the therapeutic potential of GABA in managing type 2 diabetes in a mouse model

Dysfunctional adipocytes/β-cells advance type 2 diabetes (T2D). Calorie restriction (CR) improves insulin sensitivity and fasting blood glucose (FBG) levels, while γ-aminobutyric acid (GABA) exerts regenerative effects. The impact of therapies was assessed by a high-fat diet (HFD) + streptozotocin (STZ) induced T2D mouse model. The mice were fed a CR diet (30% reduction of HFD) and treated with GABA (2.5 mg/kg i.p) for 5 weeks. Standard protocols were used to assess metabolic parameters. The mRNA expression was monitored by SYBR Green-qPCR in the targeted tissues. Oxygen consumption rate in the mitochondrial complexes was evaluated by oxytherm clark-type oxygen electrode. Pancreatic β-cell regeneration and apoptosis were analysed by immunohistochemistry. CR + GABA combination therapy showed improved metabolic parameters compared to the monotherapies. We have observed improved transcript levels of G6Pase, PEPCK, Glycogen Phosphorylase, GLUT2 and GCK in liver; ACC and ATGL in adipose tissue. Also increased SIRT-1, PGC-1α and TFAM expression; up-regulated mitochondrial complexes I-III activities were observed. We have seen increased BrdU/Insulin and PDX1/Ngn3/Insulin co-positive cells in CR + GABA treated group with a reduction in apoptotic marker (TUNEL/Insulin co-positive cells). Our results indicate that CR in combination with GABA ameliorates T2D in HFD + STZ treated mice by GABA induced β-cell regeneration, and CR mediated insulin sensitivity.

Identification and characterization of Poly(ADP-ribose) polymerase-1 interacting proteins during development of Dictyostelium discoideum

Poly (ADP-ribose) polymerase-1 (PARP-1) is a multifunctional protein that is associated with various biological processes like chromatin remodeling, DNA damage, cell death etc. In Dictyostelium discoideum, PARP-1 has also been implicated in cellular differentiation and development. However, its interacting proteins during multicellular development are not yet explored. Hence, the present study aims to identify PARP-1 interacting proteins during multicellular development of D. discoideum. BRCA1 C-terminus (BRCT) domain of PARP-1, which is mainly involved in protein-protein interactions was cloned in pGEX4T1 vector and developmental interactome of PARP-1 were analyzed by affinity purification-mass spectrometry. These interactions were further confirmed by in-silico protein-protein docking analysis, which led to identification of the proteins that show high affinity for BRCT domain. Initially, the protein structures were modeled on SWISS MODEL and PHYRE2 servers, refined by 3Drefine and validated by PROCHECK. Further, interaction sites of BRCT and the conserved regions in all interacting proteins were predicted using cons-PPISP and ConSurf, respectively. Finally, protein-protein docking analysis was done by HADDOCK. Our results identified 19 possible BRCT interacting proteins during D. discoideum development. Furthermore, interacting residues involved in the interactions and functional regions were explored. This is the first report where PARP-1's developmental interactome in D. discoideum is well established. The current findings demonstrate PARP-1's developmental interactome in D. discoideum and provide the groundwork to understand its regulated functions in developmental biology which would undoubtedly extend our perception towards developmental diseases in higher complex organisms and their treatment.

PAK5-mediated AIF phosphorylation inhibits its nuclear translocation and promotes breast cancer tumorigenesis

Although p21 activated kinase 5 (PAK5) is related to the progression of multiple cancers, its biological function in breast cancer remains unclear. Apoptosis-inducing factor (AIF) is a vital apoptosis factor in mitochondria, which can be released from mitochondria and enter the nucleus, causing caspase-independent apoptosis. In this study, we reveal that PAK5 inhibits apoptosis by preventing the nuclear translocation of AIF. PAK5 inhibits the release of AIF from mitochondria in breast cancer cells by decreasing the mitochondria membrane permeability and increasing the membrane potential. Furthermore, PAK5 phosphorylates AIF at Thr281 site to inhibit the formation of AIF/importin α3 complex, leading to decrease AIF nuclear translocation. Functionally, we demonstrate that PAK5-mediated AIF phosphorylation promotes the proliferation of breast cancer cells and accelerates the growth of breast cancer in vivo. Significantly, PAK5 and AIF expression in breast cancer are positively correlated with poor patient prognosis. PAK5 expression is negatively correlated with AIF nuclear translocation. These results suggest that PAK5-AIF signaling pathway may play an essential role in mammary tumorigenesis, providing a new therapeutic target for the treatment of breast cancer.

Insights into the functional aspects of poly(ADP-ribose) polymerase-1 (PARP-1) in mitochondrial homeostasis in Dictyostelium discoideum

BACKGROUND INFORMATION

Poly(ADP-ribose) Polymerase-1 (PARP-1) is predominantly a nuclear protein and involved in various cellular processes like DNA repair, cell death, development, chromatin modulation etc. PARP-1 utilizes NAD⁺ and adds negatively charged PAR moieties on the target proteins. Over-activation of PARP-1 has been shown to cause energy crisis mediated cell death in which mitochondrial homeostasis is also affected. Moreover, the presence of mitochondrial NAD⁺ pools highlights the role of PARP-1 in mitochondria. The aim of present study is to understand the physiological role of PARP-1 in regulating mitochondrial functioning by varying the levels of PARP-1 in Dictyostelium discoideum. Intra-mitochondrial PARylation was analyzed by indirect immunofluorescence. Further, the effect of altered levels of PARP-1 i.e. overexpression, downregulation, knockout and its chemical inhibition was studied on mitochondrial respiration, reactive oxygen species (ROS) levels, ATP production, mitochondrial fission-fusion, mitochondrial morphology and mitochondrial DNA (mtDNA) content of D. discoideum.

RESULTS

Our results show intra-mitochondrial PARylation under oxidative stress. Altered levels of PARP-1 caused impairment in the mitochondrial respiratory capacity, leading to elevated ROS levels and reduced ATP production. Moreover, PARP-1 affects the mitochondrial morphology and mtDNA content, alters the mitochondrial fission-fusion processes in lieu of preventing cell death under physiological conditions.

CONCLUSION

The current study highlights the physiological role of PARP-1 in mitochondrial respiration, its morphology, fission-fusion processes and mtDNA maintenance in D. discoideum.

SIGNIFICANCE

This study would provide new clues on the PARP-1's crucial role in mitochondrial homeostasis, exploring the therapeutic potential of PARP-1 in various mitochondrial diseases.