Tβ4-Ac-SDKP pathway: Any relevance for the cardiovascular system?

Ac-SDKP attenuates ER stress-stimulated collagen production in cardiac fibroblasts by inhibiting CHOP-mediated NF-κB expression

Inflammation and cardiac fibrosis are prevalent pathophysiologic conditions associated with hypertension, cardiac remodeling, and heart failure. Endoplasmic reticulum (ER) stress triggers the cells to activate unfolded protein responses (UPRs) and upregulate the ER stress chaperon, enzymes, and downstream transcription factors to restore normal ER function. The mechanisms that link ER stress-induced UPRs upregulation and NF-κB activation that results in cardiac inflammation and collagen production remain elusive. N-Acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), a natural tetrapeptide that negatively regulates inflammation and fibrosis, has been reported. Whether it can inhibit ER stress-induced collagen production in cardiac fibroblasts remains unclear. Thus, we hypothesized that Ac-SDKP attenuates ER stress-stimulated collagen production in cardiac fibroblasts by inhibiting CHOP-mediated NF-κB expression. We aimed to study whether Ac-SDKP inhibits tunicamycin (TM)-induced ER stress signaling, NF-κB signaling, the release of inflammatory cytokine interleukin-6, and collagen production in human cardiac fibroblasts (HCFs). HCFs were pre-treated with Ac-SDKP (10 nM) and then stimulated with TM (0.25 μg/mL). We found that Ac-SDKP inhibits TM-induced collagen production by attenuating ER stress-induced UPRs upregulation and CHOP/NF-κB transcriptional signaling pathways. CHOP deletion by specific shRNA maintains the inhibitory effect of Ac-SDKP on NF-κB and type-1 collagen (Col-1) expression at both protein and mRNA levels. Attenuating ER stress-induced UPR sensor signaling by Ac-SDKP seems a promising therapeutic strategy to combat detrimental cardiac inflammation and fibrosis.

Association of serum thymosin β4 with malnutrition-inflammation-atherosclerosis syndrome in peritoneal dialysis patients: a cross-sectional study

BACKGROUND

Malnutrition-inflammation-atherosclerosis (MIA) syndrome may worsen the prognosis of peritoneal dialysis (PD) patients. Serum thymosin β4 (sTβ4) protects against inflammation, fibrosis and cardiac dysfunction.

OBJECTIVES

The present study aimed to characterize the association between sTβ4 and MIA syndrome as well as to investigate the potential of regulating sTβ4 to improve the prognosis of PD patients.

METHODS

We performed a cross-sectional, single-center pilot study involving 76 PD patients. Demographic characteristics, clinical characteristics, nutritional profiles, inflammatory mediators, atherosclerosis-related factors and sTβ4 levels were collected and subjected to association analysis for sTβ4 and MIA syndrome.

RESULTS

sTβ4 levels did not significantly vary with sex or primary disease in PD patients. Ages and PD features did not vary between patients with different levels of sTβ4. PD patients with higher levels of sTβ4 had significantly higher levels of nutritional indicators, including subjective global nutritional assessment (SGA) (p < 0.001) and serum albumin (ALB) (p < 0.001) but lower levels of inflammatory and atherosclerotic indicators, including serum C reaction protein (CRP) (p = 0.009), the right common carotid artery (RCCA) intimal thickness (p < 0.001) and the left common carotid artery (LCCA) intimal thickness (p = 0.02). Correlation analysis showed that sTβ4 was positively associated with SGA (p < 0.001) and serum ALB (p < 0.001) but negatively associated with CRP (p = 0.020), RCCA intimal thickness (p < 0.001) and LCCA intimal thickness (p = 0.033). In multiple adjusted models, the prevalence of MIA syndrome was significantly decreased in PD patients with increased levels of sTβ4 when patients without MIA syndrome were compared to those with all indicators of MIA syndrome (OR = 0.996, 95% CI 0.993-0.999, p = 0.003) or those with at least one indicator of MIA syndrome (OR = 0.997, 95% CI 0.995-0.998, p < 0.001).

CONCLUSIONS

The sTβ4 level decreases in PD patients with MIA syndrome. The prevalence of MIA syndrome decreases significantly as the level of sTβ4 increases in PD patients.

Thymosin beta-4 denotes new directions towards developing prosperous anti-aging regenerative therapies

Our dream of defeating the processes of organ damage and aging remains a challenge scientists pursued for hundreds of years. Although the goal is to successfully treat the body as a whole, steps towards regenerating individual organs are even considered significant. Since initial approaches utilizing only progenitor cells appear limited, we propose interconnecting our collective knowledge regarding aging and embryonic development may lead to the discovery of molecules which provide alternatives to effectively reverse cellular damage. In this review, we introduce and summarize our results regarding Thymosin beta-4 (TB4) to support our hypothesis using the heart as model system. Accordingly, we investigated the developmental expression of TB4 in mouse embryos and determined the impact of the molecule in adult animals by systemically injecting the peptide following acute cardiac infarction or with no injury. Our results proved, TB4 is expressed in the developing heart and promotes cardiac cell migration and survival. In adults, the peptide enhances myocyte survival and improves cardiac function after coronary artery ligation. Moreover, intravenous injections of TB4 alter the morphology of the adult epicardium, and the changes resemble the characteristics of the embryo. Reactivation of the embryonic program became equally reflected by the increased number of cardiac vessels and by the alteration of the gene expression profile typical of the embryonic state. Moreover, we discovered TB4 is capable of epicardial progenitor activation, and revealed the effect is independent of hypoxic injury. By observing the above results, we believe, further discoveries and consequential postnatal administration of developmentally relevant candidate molecules such as TB4 may likely result in reversing aging processes and accelerate organ regeneration in the human body.

Knockout of ACE-N facilitates improved cardiac function after myocardial infarction

Angiotensin-converting enzyme (ACE) hydrolyzes N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) into inactive fragments through its N-terminal site (ACE-N). We previously showed that Ac-SDKP mediates ACE inhibitors' cardiac effects. Whether increased bioavailability of endogenous Ac-SDKP caused by knocking out ACE-N also improves cardiac function in myocardial infarction (MI)-induced heart failure (HF) is unknown. Wild-type (WT) and ACE-N knockout (ACE-NKO) mice were subjected to MI by ligating the left anterior descending artery and treated with vehicle or Ac-SDKP (1.6 mg/kg/day, s.c.) for 5 weeks, after which echocardiography was performed and left ventricles (LV) were harvested for histology and molecular biology studies. ACE-NKO mice showed increased plasma Ac-SDKP concentrations in both sham and MI group compared to WT. Exogenous Ac-SDKP further increased its circulating concentrations in WT and ACE-NKO. Shortening (SF) and ejection (EF) fractions were significantly decreased in both WT and ACE-NKO mice post-MI, but ACE-NKO mice exhibited significantly lesser decrease. Exogenous Ac-SDKP ameliorated cardiac function post-MI only in WT but failed to show any additive improvement in ACE-NKO mice. Sarcoendoplasmic reticulum calcium transport ATPase (SERCA2), a marker of cardiac function and calcium homeostasis, was significantly decreased in WT post-MI but rescued with Ac-SDKP, whereas ACE-NKO mice displayed less loss of SERCA2 expression. Our study demonstrates that gene deletion of ACE-N resulted in improved LV cardiac function in mice post-MI, which is likely mediated by increased circulating Ac-SDKP and minimally reduced expression of SERCA2. Thus, future development of specific and selective inhibitors for ACE-N could represent a novel approach to increase endogenous Ac-SDKP toward protecting the heart from post-MI remodeling.

Prepared for special issue on thymosins Thymosin β4 and the anti-fibrotic switch

Wound healing involves a rapid response to the injury by circulating cells, followed by inflammation with an influx of inflammatory cells that release various factors. Soon after, cellular proliferation begins to replace the damaged cells and extracellular matrix, and then tissue remodeling restores normal tissue function. Various factors can lead to pathological wound healing when excessive and irreversible connective tissue/extracellular matrix deposition occurs, resulting in fibrosis. The process is initiated when immune cells, such as macrophages, release soluble factors that stimulate fibroblasts. TGFβ is the most well-characterized macrophage derived pro-fibrotic mediator. Other soluble mediators of fibrosis include connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF), and interleukin 10 (IL-10). Thymosin β4 (Tβ4) has shown therapeutic benefit in preventing fibrosis/scarring in various animal models of fibrosis/scarring. The mechanism of action of Tβ4 appears related, in part, to a reduction in the inflammatory response, including a reduction in macrophage infiltration, decreased levels of TGFβ and IL-10, and reduced CTGF activation, resulting in both prevention of fibroblast conversion to myofibroblasts and production of normally aligned collagen fibers. The amino N-terminal end of Tβ4, SDKP (serine-aspartate-lysine-proline), appears to contain the majority of anti-fibrotic activity and has shown excellent efficacy in many animal models of fibrosis, including liver, lung, heart, and kidney fibrosis. Ac-SDKP not only prevents fibrosis but can reverse fibrosis. Unanswered questions and future directions will be presented with regard to therapeutic uses alone and in combination with already approved drugs for fibrosis.

Ac-SDKP peptide improves functional recovery following spinal cord injury in a preclinical model

Damage to the spinal cord triggers a local complex inflammatory reaction that results in irreversible impairments or complete loss of motor function. The evidence suggested that inhibiting the pro-inflammatory macrophage/microglia (M1 subsets) and stimulating the anti-inflammatory macrophage/microglia (M2 subsets) are potential strategies for the treatment of neuroinflammation-related diseases. We evaluated the potentially protective effect of Ac-SDKP as an endogenous tetrapeptide on rat spinal cord injury (SCI). Wistar rats were subjected to a weight-drop contusion model and were treated with Ac-SDKP (0.8 mg/kg) given subcutaneously once a day for 7 days starting at two clinically relevant times, at 2 h or 6 h post-injury. The effect of Ac-SDKP was assessed by motor functional analysis, real-time PCR (CD86 and CD206 mRNA), western blot (caspase-3), ELISA (TNF-a, IL-10), and histological analysis (toluidine blue staining). Ac-SDKP improved locomotor recovery and rescue motor neuron loss after SCI. Moreover, a decreased in TNF-a level as well as caspase 3 protein levels occurred in the lesion epicenter of the spinal cord following treatment. In addition, CD206 mRNA expression level increased significantly in Ac-SDKP treated rats compared with SCI. Together these data suggest that Ac-SDKP might be a novel immunomodulatory drug. It may be beneficial for the treatment of SCI with regards to increasing CD206 gene expression and suppress inflammatory cytokine to improve motor function and reducing histopathological lesion.

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) mitigates the liver fibrosis via WTAP/m6A/Ptch1 axis through Hedgehog pathway

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous tetrapeptide with potential antifibrotic effect. However, the underlying mechanism in the anti-fibrosis is still unclear. Here, we try to investigate its biofunction and deeplying mechanism in liver fibrosis. Rats were administrated with carbon tetrachloride (CCl4) for liver fibrosis model. The roles of AcSDKP on hepatic stellate cells (HSCs) were detected in vitro using isolated cells treated by TGF-β1. The m⁶A profie of HSCs was screened by methylated RNA immunoprecipitation sequencing (MeRIP-Seq). Results demonstrated that AcSDKP inhibited apoptosis through Hedgehog pathway in the CCl₄-induced rat HSCs. Moreover, the administration of AcSDKP decreased the N⁶-methyladenosine (m⁶A) methyltransferase WTAP (Wilms' tumour 1-associated protein) expression. Mechanistically, WTAP targeted the 3'-UTR of Ptch1 mRNA, and administration of AcSDKP reduced the stability of Ptch1 mRNA. Thus, these findings revealed an anti-fibrosis axis of AcSDKP/WTAP/m⁶A/Ptch1 in liver fibrosis. Our results identify a novel role of AcSDKP in liver fibrosis via m⁶A modification and Hedgehog pathway, which helps us to shed light on the molecular mechanism in liver fibrosis progression.

Classical and Counter-Regulatory Renin-Angiotensin System: Potential Key Roles in COVID-19 Pathophysiology

In the current COVID-19 pandemic, severe acute respiratory syndrome coronavirus 2 uses angiotensin-converting enzyme-2 (ACE-2) receptors for cell entry, leading to ACE-2 dysfunction and downregulation, which disturb the balance between the classical and counter-regulatory renin-angiotensin system (RAS) in favor of the classical RAS. RAS dysregulation is one of the major characteristics of several cardiovascular diseases; thus, adjustment of this system is the main therapeutic target. RAS inhibitors-particularly angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor blockers (ARBs)-are commonly used for treatment of hypertension and cardiovascular disease. Patients with cardiovascular diseases are the group most commonly seen among those with COVID-19 comorbidity. At the beginning of this pandemic, a dilemma occurred regarding the use of ACEIs and ARBs, potentially aggravating cardiovascular and pulmonary dysfunction in COVID-19 patients. Urgent clinical trials from different countries and hospitals reported that there is no association between RAS inhibitor treatment and COVID-19 infection or comorbidity complication. Nevertheless, the disturbance of the RAS that is associated with COVID-19 infection and the potential treatment targeting this area have yet to be resolved. In this review, the link between the dysregulation of classical RAS and counter-regulatory RAS activities in COVID-19 patients with cardiovascular metabolic diseases is investigated. In addition, the latest findings based on ACEI and ARB administration and ACE-2 availability in relation to COVID-19, which may provide a better understanding of the RAS contribution to COVID-19 pathology, are discussed, as they are of the utmost importance amid the current pandemic.

Utilizing Developmentally Essential Secreted Peptides Such as Thymosin Beta-4 to Remind the Adult Organs of Their Embryonic State-New Directions in Anti-Aging Regenerative Therapies

Our dream of defeating the processes of aging has occupied the curious and has challenged scientists globally for hundreds of years. The history is long, and sadly, the solution is still elusive. Our endeavors to reverse the magnitude of damaging cellular and molecular alterations resulted in only a few, yet significant advancements. Furthermore, as our lifespan increases, physicians are facing more mind-bending questions in their routine practice than ever before. Although the ultimate goal is to successfully treat the body as a whole, steps towards regenerating individual organs are even considered significant. As our initial approach to enhance the endogenous restorative capacity by delivering exogenous progenitor cells appears limited, we propose, utilizing small molecules critical during embryonic development may prove to be a powerful tool to increase regeneration and to reverse the processes associated with aging. In this review, we introduce Thymosin beta-4, a 43aa secreted peptide fulfilling our hopes and capable of numerous regenerative achievements via systemic administration in the heart. Observing the broad capacity of this small, secreted peptide, we believe it is not the only molecule which nature conceals to our benefit. Hence, the discovery and postnatal administration of developmentally relevant agents along with other approaches may result in reversing the aging process.

Thymosin β4: A Multi-Faceted Tissue Repair Stimulating Protein in Heart Injury

Thymosin Beta-4 (Tβ4) is known as a major pleiotropic actin-sequestering protein that is involved in tumorigenesis. Tβ4 is a water-soluble protein that has different promising clinical applications in the remodeling and ulcerated tissues repair following myocardial infarction, stroke, plasticity and neurovascular remodeling of the Peripheral Nervous System (PNS) and the Central Nervous System (CNS). On the other hand, similar effects have been observed for Tβ4 in other kinds of tissues, including cardiac muscle tissue. In recent reports, as it activates resident epicardial progenitor cells and modulates inflammatory-caused injuries, Tβ4 has been suggested as a promoter of the survival of cardiomyocytes. Furthermore, Tβ4 may act in skeletal muscle and different organs in association/synergism with numerous other tissue repair stimulating factors, including melatonin and C-fiber-derived peptides. For these reasons, the present review highlights the promising role of Tβ4 in cardiac healing.

N-acetyl-seryl-aspartyl-lysyl-proline treatment protects heart against excessive myocardial injury and heart failure in mice

Myocardial infarction (MI) in mice results in cardiac rupture at 4-7 days after MI, whereas cardiac fibrosis and dysfunction occur later. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) has anti-inflammatory, anti-fibrotic, and pro-angiogenic properties. We hypothesized that Ac-SDKP reduces cardiac rupture and adverse cardiac remodeling, and improves function by promoting angiogenesis and inhibiting detrimental reactive fibrosis and inflammation after MI. C57BL/6J mice were subjected to MI and treated with Ac-SDKP (1.6 mg/kg per day) for 1 or 5 weeks. We analyzed (1) intercellular adhesion molecule-1 (ICAM-1) expression; (2) inflammatory cell infiltration and angiogenesis; (3) gelatinolytic activity; (4) incidence of cardiac rupture; (5) p53, the endoplasmic reticulum stress marker CCAAT/enhancer binding protein homology protein (CHOP), and cardiomyocyte apoptosis; (6) sarcoplasmic reticulum Ca2+ ATPase (SERCA2) expression; (7) interstitial collagen fraction and capillary density; and (8) cardiac remodeling and function. Acutely, Ac-SDKP reduced cardiac rupture, decreased ICAM-1 expression and the number of infiltrating macrophages, decreased gelatinolytic activity, p53 expression, and myocyte apoptosis, but increased capillary density in the infarction border. Chronically, Ac-SDKP improved cardiac structures and function, reduced CHOP expression and interstitial collagen fraction, and preserved myocardium SERCA2 expression. Thus, Ac-SDKP decreased cardiac rupture, ameliorated adverse cardiac remodeling, and improved cardiac function after MI, likely through preserved SERCA2 expression and inhibition of endoplasmic reticulum stress.