Thymosin beta-4 is the main actin-sequestering protein in mammalian cells and a well-studied tissue repair molecule. What its active sites do, what the wound, cardiac and neurological models showed, what 'TB-500' refers to, and how to verify the material you are working with.
Thymosin beta-4 (Tβ4) is a 43-amino-acid, roughly 5 kDa protein found in essentially all cells and body fluids [6][7]. It was first isolated from calf thymus and was originally thought to be a thymic hormone [5]. Its main job inside the cell turned out to be structural: it is the principal protein that holds actin in its monomeric form. Over the past three decades, researchers have also found that Tβ4 promotes cell migration, angiogenesis and repair in several injury models [1]. This article covers that biology, what the key experiments measured, and a naming question that matters to anyone ordering material labeled 'TB-500.'
Cells keep a large reserve of unpolymerized actin so they can build filaments quickly when they need to move, divide or change shape. In 1991, Safer and colleagues showed that a peptide called 'Fx,' which held most of the unpolymerized actin in resting human platelets, was identical in sequence to thymosin β4 [5]. Purified Tβ4 formed a 1:1 complex with actin monomers (G-actin) and inhibited their polymerization into filaments. Tβ4 is now regarded as the major actin-sequestering molecule in eukaryotic cells [1].
This is why the literature describes Tβ4 as an actin-sequestering protein that 'moonlights' in tissue repair [1]. Its intracellular role is housekeeping. The repair-related activities in the literature mostly come from adding Tβ4 or its fragments to cells or tissue from outside, and several have been traced to specific short regions of the molecule [6].
A 2010 review by Sosne and colleagues mapped several biological activities to short sequences within Tβ4 [6]:
The actin-binding motif's role in angiogenesis was shown directly by Philp and colleagues [7]. Using native Tβ4, proteolytic fragments and synthetic peptides, they found that the seven-residue actin-binding motif was essential. In human umbilical vein endothelial cell migration assays and chick aortic arch sprouting assays, full-length Tβ4 and the actin-binding peptide showed near-identical activity at around 50 nM, while peptides lacking any part of the motif were inactive. Adding soluble actin inhibited the effect.
The N-terminal fragment has its own biology. Prolyl oligopeptidase is the main enzyme that cleaves Tβ4 to release Ac-SDKP, and this Tβ4-POP-Ac-SDKP axis has been studied in liver, kidney, heart and lung fibrosis models [12]. For experimental design, this means a full-length Tβ4 preparation can produce more than one active species in tissue.
The name TB-500 is not used consistently. In the doping-control literature it refers to a veterinary preparation whose key ingredient is the N-terminally acetylated heptapeptide LKKTETQ, a synthetic version of the actin-binding region; Ho and colleagues developed an LC-MS method to detect it and its metabolites in horse urine and plasma [8]. Many research suppliers use the same name for the full-length 43-residue sequence.
Northbridge Research Labs' TB-500 product page lists the full 43-residue sequence, a molecular formula of C₂₁₂H₃₅₀N₅₆O₇₈S and a molecular weight of 4,963.44 Da, which correspond to full-length thymosin β4. When you compare published results with your own, check which molecule a paper used. A heptapeptide and a 5 kDa protein differ in size, in how quickly they are cleared, and in whether they can release Ac-SDKP. Mass spectrometry tells them apart immediately.
The founding wound study by Malinda and colleagues used a rat full-thickness wound model [2]. Compared with saline controls, Tβ4 increased re-epithelialization by 42% at day 4 and by as much as 61% at day 7, and wounds contracted at least 11% more by day 7. Tβ4-exposed wounds showed more collagen deposition and angiogenesis. In a Boyden chamber assay, Tβ4 increased keratinocyte migration two- to threefold. The same group later reported that Tβ4 promotes angiogenesis and wound repair in both young and aged rodents, and increases hair growth [4].
Two Nature papers shaped the cardiac work. Bock-Marquette and colleagues showed that Tβ4 promoted migration of myocardial and endothelial cells in the embryonic heart and improved survival of cultured cardiomyocytes [3]. Mechanistically, Tβ4 formed a complex with PINCH and integrin-linked kinase (ILK), leading to activation of the survival kinase Akt. After coronary artery ligation in mice, Tβ4 raised ILK and Akt activity, improved early myocyte survival and improved cardiac function. Smart and colleagues then showed that Tβ4 is required for coronary vessel development in mice and that it stimulates outgrowth from quiescent adult epicardial explants, with differentiation into fibroblasts, smooth muscle cells and endothelial cells [9]. In that work, knocking down Tβ4 reduced Ac-SDKP levels, and Ac-SDKP enhanced endothelial differentiation of epicardium-derived precursors but could not rescue Tβ4-mutant hearts.
In a rat model of embolic middle cerebral artery occlusion, Morris and colleagues reported improved scores on the adhesive-removal test and modified Neurological Severity Score in Tβ4-exposed animals compared with saline controls [10]. Lesion volume did not differ between groups. The improvement instead tracked with more myelinated axons, higher vessel density at the ischemic boundary, and more oligodendrocyte progenitor cells and myelinating oligodendrocytes, which the authors proposed as the basis for recovery. It is a useful example of a functional outcome that is not explained by tissue sparing.
Clinical development of Tβ4 has used specific pharmaceutical formulations. In one small randomized, double-masked, placebo-controlled phase 2 trial in nine patients with severe dry eye, Tβ4 eye drops (RGN-259) were reported to reduce ocular discomfort and corneal fluorescein staining compared with vehicle [11]. These are findings of that trial in that formulation. They are not evidence about any research-grade material, including ours.
The foundational papers use well-characterized methods. For actin binding, researchers use native gel shift of the Tβ4-actin complex and polymerization assays [5]. For migration, Boyden chamber and transwell assays with keratinocytes or endothelial cells [2][7]. For angiogenesis, endothelial tube formation and chick aortic arch or aortic ring sprouting, with soluble actin as a mechanistic control [7]. For signaling, co-immunoprecipitation of the ILK-PINCH complex and Akt phosphorylation readouts [3]. In vivo, full-thickness excisional wounds with re-epithelialization and contraction measurements [2], coronary ligation with functional imaging [3], epicardial explant outgrowth [9], and embolic stroke with behavioral scoring and oligodendrocyte markers [10]. Researchers comparing fragments should include a peptide that lacks the actin-binding motif as a negative control, as in [7].
Full-length Tβ4 is supplied as a white lyophilized powder and should be stored at -20°C, sealed and dry. Let a vial reach room temperature before opening, dissolve it in sterile water or buffer, and freeze working solutions in single-use aliquots rather than thawing the same stock repeatedly. The sequence contains a methionine at position 6, which can oxidize. On a mass spectrum, oxidation shows up as a +16 Da shift, so check for it if a solution has been stored for a long time or handled in air.
Confirm identity by mass spectrometry, which also settles whether you have the full-length protein or a short fragment, and confirm purity by HPLC. Northbridge Research Labs sends every batch for independent third-party testing, and published certificates are listed on our COA page.
Note: TB-500 (thymosin beta-4) is sold strictly for laboratory research use only. It is not for human or veterinary use. Always review current literature and institutional guidelines before adding a new compound to a study.
Studied compound
TB-500 (Thymosin Beta-4)
The same material this research covers — 99%+ purity, independently tested, with the certificate for each batch published online.
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Research Use Only: The information in this article is for educational and research purposes only. All products mentioned are intended for laboratory research use only and are not approved for human or veterinary use.