Proteostasesystems

Proteostasesystems, or proteostasis systems, refer to the cellular networks that maintain protein homeostasis by coordinating protein synthesis, folding, trafficking, and degradation. They detect misfolded or damaged proteins and respond to environmental stress and aging to restore homeostasis, prevent aggregation, and maintain cellular function.

Molecular chaperones such as Hsp70, Hsp90, small heat shock proteins, and chaperonins assist nascent chains and help refold stressed proteins. The endoplasmic reticulum provides folding and quality control for secretory and membrane proteins, with ER-associated degradation funneling misfolded luminal proteins from the ER to the cytosol for destruction.

Degradation pathways include the ubiquitin–proteasome system for soluble misfolded proteins and the autophagy–lysosome pathway for larger aggregates or damaged organelles. Substrates are tagged with ubiquitin by E1, E2, and E3 enzymes and directed to the 26S proteasome; autophagy sequesters cargo in autophagosomes that fuse with lysosomes. Chaperone-mediated autophagy also contributes in some cases.

Cellular signaling regulates proteostasis through stress responses. The heat shock response, mediated by HSF1, upregulates chaperones. The unfolded protein response links endoplasmic reticulum stress to transcriptional programs and autophagy via IRE1, PERK, and ATF6. Nutrient- and energy-sensing pathways, including mTOR, modulate proteasome activity and autophagy.

Alterations in proteostasis accompany aging and contribute to neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's disease, and amyotrophic lateral sclerosis. Therapeutic approaches seek to enhance chaperone capacity, boost degradation pathways, or reduce the burden of misfolded proteins to restore proteostasis and cellular health.