Quiescent fibroblasts exhibit high metabolic activity

Area of Science:

• Cell Biology
• Metabolic Regulation
• Mammalian Cell Physiology

Background:

• Cellular quiescence is a reversible exit from the cell cycle, often associated with reduced metabolic activity.
• Previous studies reported lower glycolytic rates in quiescent lymphocytes compared to proliferating ones.

Purpose of the Study:

• To investigate the metabolic activity of primary human fibroblasts induced into quiescence via contact inhibition.
• To determine if reduced metabolic activity is a universal characteristic of quiescent cells.

Main Methods:

• Utilized isotope labeling to trace metabolic pathways and quantify metabolic fluxes.
• Analyzed central carbon metabolism, pentose phosphate pathway, and tricarboxylic acid cycle activity.
• Assessed the impact of pentose phosphate pathway inhibition on cell viability.

Main Results:

• Contact-inhibited fibroblasts exhibit high metabolic rates, similar to proliferating cells, utilizing glucose across central carbon metabolism.
• An enhanced overflow flux from the pentose phosphate pathway to glycolysis was observed.
• A reversed flux in the tricarboxylic acid cycle (alpha-ketoglutarate to citrate) was detected, potentially for NADPH shuttling.
• Pentose phosphate pathway inhibition led to preferential apoptosis in quiescent fibroblasts.
• High metabolic activity supports protein/lipid turnover and extracellular matrix protein excretion.

Conclusions:

• Reduced metabolic activity is not a universal hallmark of cellular quiescence.
• Quiescent fibroblasts redirect high metabolic activity towards self-preservation and specialized functions.
• Metabolic reprogramming in quiescence supports organismal health beyond cell division.