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The study of key-value pair peptides has expanded dramatically over the past decade, revealing a complex network of signaling molecules that influence cellular behavior across a wide range of physiological and pathological contexts. Among these, the thymosin beta-4 fragment Ac-SDKP (N-acetyl-Ser-Asp-Lys-Pro) stands out for its multifaceted roles in tissue repair, anti-inflammatory responses, and modulation of cell migration. This peptide is derived from the larger precursor protein thymosin β-4 (Tβ4), a ubiquitous actin-binding polypeptide that participates in cytoskeletal rearrangement, angiogenesis, and wound healing.



Thymosin Beta-4 Fragment (Ac-SDKP)



Ac-SDKP is a tetrapeptide composed of serine, aspartic acid, lysine, and proline. Its N-terminal acetylation confers resistance to proteolytic degradation, thereby extending its half-life in extracellular fluids. The peptide functions as an endogenous regulator of the renin–angiotensin system (RAS) by inhibiting angiotensin‐converting enzyme (ACE), which reduces the production of angiotensin II and its downstream pro-fibrotic signaling pathways. In addition, Ac-SDKP can bind to integrin receptors on endothelial cells, triggering intracellular cascades that promote cell migration, proliferation, and tube formation—key steps in angiogenesis.



About Thymosin Beta-4 Fragment (Ac-SDKP)



The biological effects of Ac-SDKP are mediated through several mechanisms. First, its ACE inhibition leads to a decrease in angiotensin II levels, which dampens oxidative stress and inflammatory cytokine release. Second, the peptide activates protein kinase C (PKC) and extracellular signal-regulated kinases (ERK1/2), enhancing transcription of genes involved in cell survival and matrix remodeling. Third, Ac-SDKP stimulates the release of growth factors such as vascular endothelial growth factor (VEGF) and transforming growth factor-β (TGF-β) from resident stromal cells, further supporting tissue regeneration. Importantly, clinical studies have demonstrated that systemic administration of Ac-SDKP can attenuate organ fibrosis in models of kidney injury, cardiac hypertrophy, and liver cirrhosis.



Found In



Ac-SDKP is present in a variety of biological fluids and tissues. It is released from platelets during clot formation and circulates in the plasma at nanomolar concentrations. The peptide is also detected in the cerebrospinal fluid, where it may play neuroprotective roles by limiting microglial activation. In the kidney, Ac-SDKP is abundant within the tubular epithelium and interstitial spaces, contributing to the maintenance of renal architecture during repair processes. Additionally, the fragment can be identified in cardiac tissue following myocardial infarction, suggesting a role in cardiomyocyte survival and scar remodeling.



In summary, Ac-SDKP exemplifies how small peptide fragments derived from larger proteins can exert powerful regulatory effects on multiple signaling pathways. Its capacity to modulate ACE activity, promote angiogenesis, and reduce fibrosis makes it an attractive candidate for therapeutic development in cardiovascular, renal, and hepatic diseases. Ongoing research continues to uncover new receptors, downstream effectors, and potential combinatorial treatments that harness the full spectrum of Ac-SDKP’s biological activities.

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