P21
preclinicalAlso known as: P021
**Mechanism of Action** P21 (P021) is a synthetic peptide derived from ciliary neurotrophic factor (CNTF) that acts as a small-molecule mimetic of CNTF's neuroprotective signaling. It selectively activates the CNTF receptor complex (CNTFRα, gp130, and LIFRβ), leading to downstream JAK/STAT3 and MAPK/ERK pathway activation. This signaling cascade promotes neural stem cell proliferation and differentiation, particularly in the hippocampus, while simultaneously reducing tau hyperphosphorylation and aggregation through modulation of glycogen synthase kinase-3β (GSK-3β) activity. The peptide does not cross the blood-brain barrier efficiently, but systemic administration has shown central effects, likely via peripheral signaling or circumventricular organ interactions. **Key Research Findings** Preclinical studies in transgenic Alzheimer's disease (AD) mouse models (e.g., 3xTg-AD) demonstrate that chronic P21 treatment enhances hippocampal neurogenesis, improves spatial memory in Morris water maze tests, and reduces soluble and insoluble tau pathology by 30–50%. The peptide also decreases neuroinflammation markers (e.g., IL-6, TNF-α) and restores synaptic plasticity markers (e.g., PSD-95, synaptophysin). Notably, P21 does not significantly alter amyloid-β plaque burden, suggesting its effects are tau-centric and neurogenic rather than amyloid-directed. No overt toxicity has been reported in rodent studies. **Clinical Relevance** P21 remains in preclinical development, with no human trials initiated to date. Its dual action—promoting neurogenesis and targeting tau pathology—positions it as a potential disease-modifying candidate for AD and other tauopathies. However, challenges include optimizing bioavailability and confirming target engagement in humans. The peptide's CNTF-derived mechanism may also carry risks of weight loss or immune modulation, as seen with full-length CNTF. For research purposes only — not medical advice.
Key data
Research & studies
P21 expression was significantly reduced in OA cartilage and negatively correlated with disease severity.; P21 overexpression enhanced chondrocyte anabolism, alleviated oxidative stress, and suppressed catabolic responses, while P21 deficiency worsened cartilage degeneration.; DHA restored P21 levels and modulated PI3K/AKT signaling, promoting anabolic markers (SOX9, COL2, ACAN) and suppressing catabolic markers (MMP13, ADAMTS-4, COL10).; DHA@HAMA nanoparticles showed improved stability, compatibility, and sustained release, further enhancing P21-mediated chondroprotection and reducing OA severity.
p21 shRNA achieved ~80% reduction in p21 mRNA in vitro and increased G2M phase cells; p21 shRNA treatment significantly improved cartilage repair in both immunocompromised and immunocompetent mice; Tissue cytometry showed 90% transduction efficiency with p21+ cells reduced from ~90% to ~30%; Spearman correlation showed a significant negative correlation between p21 expression and repair outcomes
Cytoplasmic p21 increased spheroid formation and CD133 expression in a mechanism partly dependent on AKT activation.; Phosphomimetic p21 (T145D) enhanced stemness factors (Oct3/4, Nanog, Sox2), while nuclear p21 (T145A) reduced them.; Cytoplasmic p21 interacts with the NF-κB-IκB complex, promoting NF-κB activation and upregulation of BCL-xL and COX2.; Screening p21 subcellular localization may stratify CRC patients with high metastatic risk for CSC-targeted therapies.
p21 is primarily a cell cycle regulator linking DNA damage responses to apoptosis, senescence, and cell cycle arrest.; Accumulating evidence links p21 both directly and indirectly to various metabolic processes.; Recent investigations indicate p21 significantly contributes to the pathogenesis of diabetes.; Therapies targeting p21 are reviewed as potential approaches to alleviate metabolic disorders.
p21-mNeonGreen expression correlates with indel frequencies, useful for gRNA screening.; Double-stranded ODNs and AAVs trigger stronger p21 activation than single-stranded forms.; Lentiviral vectors induce lower p21 expression than AAVs, making them preferable for sensitive cells.; Viral promoter selection, such as SFFV, significantly affects p21 activation levels.
Loss of p21 increases trabecular bone formation post-injury.; Loss of E2f1 increases cortical bone formation but leads to poorer bone repair overall.; E2f1 absence dramatically decreases osteoblasts, osteoclasts, and chondrocytes at the injury site.; E2f1 and p21 have distinct roles in bone regeneration, with E2f1 regulating cell populations required for repair.
p21 knockout reduced senescent cell presence and alleviated chronic lung inflammation pathology in mice.; p21 knockout improved the fitness of mice subjected to chronic LPS exposure.; Resident epithelial and endothelial cells, not immune cells, mediate p21-dependent inflammatory responses.; p21 is implicated as a critical regulator and driver of chronic airway inflammation and lung destruction.
p21 -/- mice had lower Allen scores for fracture healing than wild-type mice; p21 -/- mice exhibited larger calluses and lower bone mineral density; p21 -/- mice showed delayed endochondral ossification via the Ihh-Runx2-Osterix pathway in vivo; Down-regulation of p21 in ATDC5 cells delayed endochondral ossification in vitro
Frequently asked questions
What is P21?
**Mechanism of Action** P21 (P021) is a synthetic peptide derived from ciliary neurotrophic factor (CNTF) that acts as a small-molecule mimetic of CNTF's neuroprotective signaling. It selectively activates the CNTF receptor complex (CNTFRα, gp130, and LIFRβ), leading to downstream JAK/STAT3 and MAPK/ERK pathway activat
How does P21 work?
CNTF-derived peptidergic compound that promotes neurogenesis and reduces tau pathology in preclinical Alzheimer's models.
What is the research status of P21?
P21 is currently classified as preclinical, with 41,480 research references on record. This is for research purposes only and is not medical advice.
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