Subcellular NAD⁺ pools are interconnected and buffered by mitochondrial NAD.

Area of Science:

• Cellular Biology
• Metabolism
• Aging Research

Background:

• Nicotinamide adenine dinucleotide (NAD+) is crucial for cellular signaling and energy metabolism.
• NAD+ levels decline with age, impacting cellular function.
• The mechanisms by which cells adapt to persistently low NAD+ are not fully understood.

Purpose of the Study:

• To investigate how cells cope with chronic, compartment-specific NAD+ depletion.
• To elucidate the role of mitochondria in maintaining NAD+ homeostasis.
• To understand the impact of targeting mitochondrial NAD+ pools.

Main Methods:

• Engineered cell lines with stable PARP activity in various subcellular compartments.
• Utilized isotope-tracer flux measurements.
• Employed mathematical modeling to analyze NAD+ dynamics.

Main Results:

• Engineered NAD+ consumption reduced cellular NAD+ by up to 50%.
• Lowered NAD+ concentrations kinetically restricted consumption, balancing biosynthesis.
• Mitochondria maintain NAD+ via SLC25A51 import and NMNAT3-dependent cleavage, creating a virtual NAD+ pool.
• Mitochondrial NAD+ depletion was detrimental, unlike other compartment targeting.

Conclusions:

• Cellular NAD+ pools are interconnected, with mitochondria playing a key regulatory role.
• Mitochondria can buffer NAD+ levels, explaining tolerance to some age-related decline.
• Targeting mitochondrial NAD+ is critical, as this pool is essential for cellular resilience.