P21 5mg – Research Grade Cognitive Peptide

P21 (sometimes written as Peptide 021) is an 11-amino-acid synthetic peptide derived from a region of ciliary neurotrophic factor (CNTF), studied in preclinical neurogenesis and cognitive-aging research by Khalid Iqbal and colleagues at the New York State Institute for Basic Research in Developmental Disabilities. CNTF itself is a neurotrophic cytokine that supports the survival and differentiation of motor neurons and a range of CNS neuronal and glial populations. The research-supply P21 peptide was designed and characterized as a small, blood-brain-barrier-penetrating peptide that retains a portion of the proposed neurogenic and neuroprotective activity of full-length CNTF while removing the larger protein's pharmacological limitations.

The peptide has been investigated in published preclinical research in rodent models of adult-hippocampal neurogenesis, cognitive-aging, and neurodegenerative pathology. Reported endpoints include hippocampal neurogenesis measurements (BrdU/Ki67-positive newborn neurons in the dentate gyrus, doublecortin-positive immature neurons), cognitive-behavioral measures in aging and disease-model rodents (Morris water maze, novel-object recognition), and biochemical measurements of synaptic markers and neurotrophin pathway signaling. The published work is preclinical and the peptide is not under clinical-research development for any indication as of the publication of this reference.

This page is a research-only educational reference for P21 as a research peptide for neurogenesis and cognitive-aging preclinical research. The peptide is not approved as a medicine and is not the subject of any clinical-research program. No medical or therapeutic claims are made on this page.

P21 is an 11-amino-acid synthetic peptide derived from a region of ciliary neurotrophic factor (CNTF). The peptide was designed in the laboratory of Khalid Iqbal at the New York State Institute for Basic Research in Developmental Disabilities (Staten Island, NY) as part of a research program developing small CNTF-derived peptides intended to retain neurogenic activity while being more drug-like than the full-length cytokine. The molecule is supplied as a sterile lyophilized peptide for reconstitution and in-vivo or in-vitro use in neurogenesis research.

Ciliary neurotrophic factor is a member of the IL-6 family of cytokines, structurally a four-helix-bundle protein produced principally by Schwann cells and astrocytes. CNTF signals through a tripartite receptor complex consisting of CNTFRα (the ligand-binding component, GPI-anchored to the membrane), gp130 (the common IL-6-family signaling subunit), and LIFR (leukemia inhibitory factor receptor β). The intracellular signaling activates JAK1/JAK2 with downstream STAT3 phosphorylation, MAPK signaling, and PI3K/Akt signaling, with downstream cellular effects including neuronal survival, neurite outgrowth, neuronal differentiation of neural progenitors, and immunomodulatory effects on microglia and astrocytes.

CNTF itself was investigated as a potential therapeutic for amyotrophic lateral sclerosis (ALS) in clinical trials in the 1990s but failed to demonstrate efficacy in pivotal studies. CNTF and its analogs have subsequently been studied in research on neurodegenerative diseases, on retinal degeneration (encapsulated cell technology delivering CNTF intravitreally has been studied in macular degeneration), and on metabolic regulation (CNTF has effects on hypothalamic feeding circuits relevant to obesity research; this work led to the clinical development of the CNTF analog axokine, which was discontinued for clinical-development reasons unrelated to acute mechanistic failure).

The P21 peptide design rationale was to identify a short sequence within CNTF that retains a portion of the proposed neurogenic signaling activity, with small size and physicochemical properties supporting blood-brain-barrier penetration after peripheral administration. The published characterization in the Iqbal laboratory and collaborating groups includes measurements of brain penetration after peripheral administration, of neurogenic activity in cultured neural progenitor systems, and of cognitive and neurogenesis endpoints in rodent models of normal aging, of trisomy-related cognitive impairment (Ts65Dn mouse model of Down syndrome), and of Alzheimer-related pathology (triple-transgenic 3xTg-AD mouse model).

The reported preclinical effects include increased hippocampal neurogenesis (newborn-neuron counts in the dentate gyrus by BrdU and doublecortin staining), increased markers of mature synaptic function (PSD-95, synaptophysin), increased BDNF expression, and improvements in performance on spatial-memory and object-recognition behavioral tests in aged and disease-model rodents. The proposed mechanism involves engagement of the CNTF receptor signaling pathway by the peptide, although the receptor-binding characterization of P21 specifically is less detailed than the parent CNTF receptor pharmacology.

It is important to be clear about what P21 is not. It is not a medicine — there are no approved indications for P21 or for any CNTF-derived peptide. It is not a clinical-research compound — there are no clinical trials of P21 in human subjects as of the publication of this reference. It is not equivalent to dihexa, NSI-189, or other unrelated cognitive-research peptides — the molecule has a specific CNTF-derived sequence and a specific research literature distinct from those compounds.

Ciliary neurotrophic factor was originally identified in the 1980s as a factor in extracts of the chick ciliary ganglion that supported the survival of ciliary neurons in culture. The protein was purified, characterized, and cloned in the late 1980s, establishing its place in the IL-6 cytokine family. Through the 1990s, CNTF was investigated as a candidate therapeutic for motor-neuron disease (amyotrophic lateral sclerosis, ALS), motivated by preclinical evidence that CNTF supported motor-neuron survival in culture and in animal models of motor-neuron injury. Pivotal clinical trials of recombinant CNTF in ALS did not demonstrate efficacy and were terminated.

In parallel, CNTF and CNTF analogs were investigated in metabolic-research contexts including obesity, with the observation that CNTF has potent effects on hypothalamic feeding circuits and produces sustained weight loss in animal models. The CNTF analog axokine (a recombinant variant developed by Regeneron Pharmaceuticals) advanced into clinical trials for obesity in the early 2000s with promising weight-loss effects but was discontinued due to immunogenicity (development of anti-axokine antibodies in a fraction of subjects, which neutralized the effect). The IL-6-family receptor pharmacology of CNTF remains a topic of basic-science research interest.

The P21 peptide design program at the New York State Institute for Basic Research in Developmental Disabilities under Khalid Iqbal pursued a different translational direction: identifying small CNTF-derived peptides as research-tool compounds for neurogenesis and cognitive-aging research, rather than full-length CNTF replacement. The molecule was characterized in published research starting in the 2010s with reports of brain penetration after peripheral administration, neurogenic activity in cell-culture models, and cognitive and neurogenesis endpoints in rodent models of aging, of Down syndrome (Ts65Dn mouse model), of Alzheimer-related pathology (3xTg-AD), and of stress-related cognitive impairment.

The Iqbal laboratory has historically focused on tau pathology and Alzheimer's disease research, and the P21 program is part of a broader research portfolio investigating peptide-based research approaches to age-related and neurodegenerative cognitive impairment. The peptide has been characterized in collaboration with other academic groups in published work investigating mechanism and downstream pathway engagement.

The P21 peptide is not under development as a medicine by any pharmaceutical sponsor as of the publication of this reference. There are no clinical trials of the peptide in human subjects. The published evidence base is preclinical in-vitro and rodent in-vivo work in the context of neurogenesis and cognitive-aging research investigation. The peptide remains a research-supply compound for academic and preclinical use.

Adult hippocampal neurogenesis is the process by which new neurons are generated from neural stem and progenitor cells in the subgranular zone of the dentate gyrus throughout adult life in many mammalian species including humans. The newborn neurons mature over a multi-week period (incorporating into the dentate granule-cell layer, developing dendritic arbors and synaptic connections) and contribute to specific aspects of hippocampal-dependent learning and memory function, particularly pattern separation and contextual discrimination. Adult hippocampal neurogenesis declines with normal aging and is further impaired in models of stress, neurodegeneration, and various disease states.

A range of growth factors, cytokines, and signaling molecules support adult neurogenesis, including BDNF, NGF, FGF2, EGF, VEGF, IGF-1, and the IL-6 cytokine family members (IL-6, CNTF, LIF, oncostatin M, cardiotrophin-1). CNTF specifically signals through the CNTFRα/gp130/LIFR receptor complex on neural stem cells and progenitors, with downstream JAK/STAT3, MAPK, and PI3K/Akt activation that supports stem-cell proliferation, neuronal differentiation, and survival of newborn neurons. The relative contribution of CNTF and other IL-6-family cytokines to baseline adult neurogenesis and to neurogenic responses to behavioral, pharmacological, and disease challenges is an active research area.

P21 is hypothesized to engage the CNTF receptor signaling pathway to support adult hippocampal neurogenesis. The proposed mechanism includes direct effects on neural stem and progenitor cell proliferation, on survival of newborn neurons, and on the maturation and synaptic integration of new neurons into the existing dentate-granule-cell circuit. Downstream effects on hippocampal expression of BDNF, synaptic-marker proteins (PSD-95, synaptophysin, GluA1), and indicators of synaptic plasticity have been reported in preclinical work in normal aging and disease-model rodents.

The blood-brain-barrier (BBB) penetration of P21 after peripheral administration is a critical design feature. The BBB is highly restrictive to most peptides; small peptides with specific physicochemical properties (low molecular weight, balanced hydrophilicity/lipophilicity, structural motifs supporting receptor-mediated or other facilitated transport) can achieve measurable brain penetration after peripheral administration. The Iqbal-laboratory characterization of P21 includes measurements of brain penetration after intraperitoneal or subcutaneous administration in rodents, supporting the use of peripheral dosing in in-vivo neurogenesis and cognitive-behavioral studies.

The preclinical-research literature on P21 includes published reports in rodent models of normal aging (with cognitive testing and hippocampal-neurogenesis measurements in aged versus young controls), of Down syndrome (Ts65Dn mouse model with cognitive testing and neurogenesis measurements), and of Alzheimer-related pathology (3xTg-AD mouse model with cognitive testing, neurogenesis measurements, and biochemistry of amyloid and tau pathology). Reported effects across these contexts include increased hippocampal newborn-neuron counts, increased markers of synaptic function, and improvements on hippocampal-dependent cognitive-behavioral tests.

Distinguishing P21 from related areas of cognitive and neurogenesis research: the peptide is not a BDNF mimetic (although BDNF expression is a downstream readout in some studies); it is not a nootropic in the broad sense of pharmacological cognitive enhancement; it is not a peptide developed for any specific clinical neurological indication. The research-application framing is mechanistic preclinical work on the CNTF-pathway neurogenesis hypothesis, conducted in rodent models with specific cognitive and neurogenesis endpoints.

P21 is an 11-amino-acid linear synthetic peptide derived from a region of ciliary neurotrophic factor. The specific sequence and any structural modifications are described in the relevant publications from the Iqbal laboratory and collaborators. The molecular weight is in the range of 1200-1300 g/mol depending on specific terminal modifications; the published preparation typically uses N-terminal and C-terminal modifications (acetylation and amidation respectively) to confer resistance to exopeptidase degradation and improve physicochemical properties for brain penetration.

The choice of the parent CNTF region for the peptide derivation reflects mechanistic work in the Iqbal laboratory identifying that this region contributes to the receptor-binding interface of full-length CNTF with the CNTFRα/gp130/LIFR receptor complex. The proposal is that the short peptide retains a portion of the receptor-engagement activity of the parent cytokine in a small, drug-like format.

Research-grade P21 is produced by solid-phase peptide synthesis (SPPS), purified by reversed-phase HPLC to ≥98% purity, and verified by analytical HPLC and mass spectrometry. The peptide is supplied as a sterile lyophilized powder in sealed vials. Lyophilized storage is at -20 °C or below in moisture-protected containers; reconstituted solutions in aqueous diluent are stored refrigerated and used within a short window per standard peptide-stability practice. The peptide has good solid-state stability and adequate solution stability under appropriate conditions.

In published preclinical research, P21 has been used in several principal application areas:

Rodent in-vivo neurogenesis studies. C57BL/6 mice and other rodent strains in normal-aging cohorts are administered P21 peripherally (intraperitoneal, subcutaneous) over multi-week periods. Adult hippocampal neurogenesis is measured by BrdU pulse-labeling combined with NeuN co-staining for newborn-neuron identification, by doublecortin (DCX) immunohistochemistry for immature neuron quantification, and by Ki67 staining for proliferating progenitor identification in the subgranular zone of the dentate gyrus.

Cognitive-behavioral testing in aging and disease models. Morris water maze (spatial reference memory), novel-object recognition (recognition memory), Y-maze and T-maze (working memory), contextual fear conditioning (hippocampal-dependent associative learning), and other hippocampal-dependent behavioral paradigms are used to evaluate cognitive effects of P21 administration in aged wild-type mice and in disease-model strains.

Down syndrome research (Ts65Dn mouse model). The Ts65Dn mouse carries a partial trisomy of mouse chromosome 16 with regional triplication overlapping with human chromosome 21 and exhibits cognitive impairments mapped to hippocampal and prefrontal-cortical function. P21 has been evaluated in this model with reports of effects on hippocampal neurogenesis measurements and on cognitive-behavioral performance.

Alzheimer-related pathology research (3xTg-AD model). The 3xTg-AD mouse expresses transgenes for human APP-Swedish, human PS1-M146V, and human tau-P301L and develops progressive amyloid and tau pathology with cognitive impairment. P21 has been evaluated in this model with reports of effects on neurogenesis, synaptic markers, and behavioral cognitive endpoints in the context of the AD-related pathological background.

Mechanistic CNTF-pathway research. Cultured neural stem and progenitor cell systems are used to investigate the cell-autonomous effects of P21 on progenitor proliferation, neuronal differentiation, and survival, and to investigate engagement of the CNTF receptor complex (CNTFRα/gp130/LIFR) and downstream JAK/STAT3/MAPK/PI3K-Akt signaling.

Stress-related cognitive impairment research. Chronic-stress rodent models that produce cognitive impairment and impaired hippocampal neurogenesis have been used to evaluate P21 administration with reports of effects on neurogenesis and behavioral cognitive measurements.

All applications are research-supply context: laboratory and academic use in rodent in-vivo models and cultured cell systems. The peptide is not for human consumption, is not a medicine, and nothing on this page describes a clinical protocol or therapeutic use.

P21 sits within the broader landscape of cognitive-research and neurogenesis peptides and small molecules, with mechanistically distinct neighbors in the academic literature.

P21 (Peptide 021) is an 11-amino-acid synthetic peptide derived from a region of ciliary neurotrophic factor (CNTF), developed in the Iqbal laboratory at the New York State Institute for Basic Research in Developmental Disabilities for preclinical neurogenesis and cognitive-aging research. The molecule is proposed to engage the CNTF receptor signaling pathway (CNTFRα/gp130/LIFR with downstream JAK/STAT3, MAPK, and PI3K/Akt activation) and to support adult hippocampal neurogenesis after peripheral administration with measurable blood-brain-barrier penetration in rodents.

Published preclinical research has investigated P21 in normal-aging rodents, in the Ts65Dn mouse model of Down syndrome, in the 3xTg-AD mouse model of Alzheimer-related pathology, and in chronic-stress paradigms, with reported effects on hippocampal newborn-neuron counts (BrdU, doublecortin, Ki67), on markers of synaptic function (PSD-95, synaptophysin), on BDNF expression, and on performance in hippocampal-dependent cognitive-behavioral tests (Morris water maze, novel-object recognition).

This page is research educational only. P21 is not an approved medicine and is not under clinical-research development for any indication. There are no clinical trials of the peptide in human subjects. Research-supply P21 is intended for laboratory and preclinical academic use; no medical or therapeutic claims are made.