Targeting NAD Metabolism for the Therapy of Age-Related Neurodegenerative Diseases

As the aging population continues to grow rapidly, age-related diseases are becoming an increasing burden on the healthcare system and a major concern for the well-being of elderly individuals. While aging is an inevitable process for all humans, it can be slowed down and age-related diseases can be treated or alleviated. Nicotinamide adenine dinucleotide (NAD) is a critical coenzyme or cofactor that plays a central role in metabolism and is involved in various cellular processes including the maintenance of metabolic homeostasis, post-translational protein modifications, DNA repair, and immune responses. As individuals age, their NAD levels decline, and this decrease has been suggested to be a contributing factor to the development of numerous age-related diseases, such as cancer, diabetes, cardiovascular diseases, and neurodegenerative diseases. In pursuit of healthy aging, researchers have investigated approaches to boost or maintain NAD levels. Here, we provide an overview of NAD metabolism and the role of NAD in age-related diseases and summarize recent progress in the development of strategies that target NAD metabolism for the treatment of age-related diseases, particularly neurodegenerative diseases.

Establishing Cell Lines Overexpressing DR3 to Assess the Apoptotic Response to Anti-mitotic Therapeutics

Studying the function of a gene of interest can be achieved by manipulating its level of expression, such as decreasing its expression with knockdown cell lines or increasing its expression with overexpression cell lines. Transient and stable transfection are two methods that are often used for exogenous gene expression. Transient transfection is only useful for short-term expression, whereas stable transfection allows exogenous genes to be integrated into the host cell genome where it will be continuously expressed. As a result, stable transfection is usually employed for research into long-term genetic regulation. Here we describe a simple protocol to generate a stable cell line overexpressing tagged death receptor 3 (DR3) to explore DR3 function. We picked single clones after a retroviral infection in order to maintain the homogeneity and purity of the stable cell lines. The stable cell lines generated using this protocol render DR3-deficient HT29 cells sensitive to antimitotic drugs, thus reconstituting the apoptotic response in HT29 cells. Moreover, the FLAG tag on DR3 compensates for the unavailability of good DR3 antibody and facilitates the biochemical study of the molecular mechanism by which antimitotic agents induce apoptosis.

Anti-mitotic chemotherapeutics promote apoptosis through TL1A-activated death receptor 3 in cancer cells

The commonly used antimitotic chemotherapeutic agents such as taxol and vinblastine arrest cell cycle progression by disrupting mitotic spindles, and cause cancer cells to undergo apoptosis through ‘mitotic catastrophe’. The molecular mechanisms by which these drugs induce apoptosis and their relevance to clinical efficacy are not known. Facilitated by a new spindle poison diazonamide, we found that apoptosis induced by these agents requires death receptor 3 (DR3). Mitotic arrest by these agents induces lysosome-dependent secretion of the DR3 ligand, TL1A. Engagement of TL1A with DR3 stimulates the formation of FADD-containing and caspase-8-containing death-inducing signaling complex (DISC), which subsequently activates apoptosis in cells that express DR3. Expression of DR3 and TL1A correlates with the apoptotic response of human tumor xenograft models and human cancer cell lines to antimitotic drugs, providing further evidence that these drugs kill cancer cells through the DR3/TL1A-mediated pathway. These results suggest that TL1A and DR3 may hold promise to be used as biomarkers for predicting clinical response to antimitotic therapeutics.