Inadequate protein intake affects skeletal muscle transcript profiles in older humans

Area of Science:

• Nutritional biochemistry
• Skeletal muscle physiology
• Molecular biology

Background:

• Inadequate dietary protein intake negatively impacts skeletal muscle morphology and function.
• Early alterations in muscle messenger RNA (mRNA) levels may indicate these adverse changes.

Purpose of the Study:

• To investigate if insufficient protein intake differentially affects skeletal muscle transcript concentrations and expression profiles in older adults.
• To identify specific gene expression changes associated with short-term inadequate protein intake.

Main Methods:

• Older adults (55-80 years) consumed controlled diets for two weeks: adequate protein (1.2 g/kg/d) followed by either inadequate protein (0.5 g/kg/d) or adequate protein (control).
• Vastus lateralis muscle biopsy samples were collected for RNA isolation.
• Microarray analysis was used to measure transcript levels in the inadequate protein group, with real-time polymerase chain reaction (PCR) for validation.

Main Results:

• Inadequate protein intake resulted in 85 differentially expressed transcripts (FDR corrected), with 54 up-regulated and 31 down-regulated.
• Affected transcripts were involved in immune/inflammatory responses, muscle contraction/development, extracellular matrix, energy metabolism, protein synthesis, and proliferation.
• Real-time PCR confirmed diet-related expression differences in 9 transcripts.

Conclusions:

• Short-term inadequate protein intake induces significant changes in skeletal muscle transcript levels in older humans.
• These transcriptomic alterations may precede detrimental metabolic, functional, and structural consequences, including muscle wasting.