Peptide‐mediated activation of Akt and extracellular regulated kinase signaling prevents lymphocyte apoptosis

Abstract

Lymphocyte apoptosis is a hallmark of sepsis and contributes to disease mortality. In other acute injuries, such as myocardial and cerebral ischemia/reperfusion, apoptosis plays a significant role in disease-associated morbidity and mortality. We previously showed that constitutive activation of the potent antiapoptotic Akt/protein kinase B signaling pathway in lymphocytes both reduces sepsisinduced lymphocyte apoptosis and confers a significant survival advantage compared to wild-type littermates. Here, we demonstrate a therapeutic approach to acutely augment Akt activity in a wildtype animal. A cell-permeable peptide conjugated to the Akt-binding domain of the endogenous Akt coactivator, Tcl-1, prolongs Akt activity, activates extracellular regulated kinase (ERK) signaling and protects lymphocytes from numerous apoptotic stimuli both in vitro and in vivo. Molecular approaches to activate the antiapoptotic Akt and ERK signaling pathways may provide a novel tool to study these signaling pathways, as well as a new antiapoptotic strategy for the treatment of sepsis and other acute injuries.SEPSIS AFFECTS 750,000 PATIENTS in the United States annually with nearly 30% mortality (1). Despite advances in patient care, the number of cases continues to rise. One difficulty in treating sepsis is that the pathogen causing infection is frequently not identified. As a result, it is difficult to know whether a therapeutic regimen is appropriate, and thus empiric antibiotics are often given. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptAlthough a number of approaches are being explored to better diagnose and stage patients with sepsis, none have reached maturity (2).An alternative to current, pathogen-targeted therapies is the development of therapeutic approaches that ameliorate the pathological aspects of the host response (3-6). A common histopathological finding in septic patients at autopsy and in animal models of sepsis is the profound loss of lymphocytes by apoptosis (7). Prevention of sepsis-induced lymphocyte apoptosis confers a significant survival advantage in animal models of disease (8,9). One transgenic mouse that has a significant survival advantage in models of sepsis overexpresses Akt in a T-lymphocyte-restricted manner (10). These mice express a variant of Akt that has an N-terminal myristoylation sequence that results in Akt being constitutively active. Akt is a serine-threonine protein kinase that is activated in response to cell-stimulatory signals, such as growth factors, cytokines, and T cell activation. Akt inactivates a number of proapoptotic molecules, including GSK-3β, Bad, and forkhead transcription factors. As a result, activation of Akt renders a cell transiently refractory to apoptotic stimuli.Endogenous Akt is activated in response to many cell stimuli, however, these stimuli initiate a number of other cellular processes that are independent of Akt. The recent failure of anti-CD28 in phase I safety trials highlights the danger of activating several cell sign...

Overcoming Amino-Nogo-induced Inhibition of Cell Spreading and Neurite Outgrowth by 12-O-Tetradecanoylphorbol-13-acetate-type Tumor Promoters

“…These authors further indicated that inactivation of GSK3 promoted axonal growth and recovery (46). Importantly, we showed that activation of Akt1 by a cell-permeable TCL1 peptide (19), which facilitated Akt oligomerization and led to its activation, significantly reversed amino-Nogo inhibition of cell spreading. Also, the inhibition of neurite outgrowth by myelin was reversed in the presence of TCL1 peptide.…”

“…NSC23766, Gö-6983, Gö-6976, and Akt inhibitor VII (TAT-Akt-in) were purchased from Calbiochem. Synthetic peptides TAT-TCL-1 and TAT-TCL-1G (19) were synthesized by NeoMPS, Inc. with purity of Ͼ96% by HPLC. Anti-Rac1 clone 23A8, anti-Akt1, and anti-phospho-Akt (Ser 473 ) clone 11E6 were purchased from Millipore.…”

“…5A). Next, a cell-permeable peptide that contains the Akt-binding domain of the endogenous Akt coactivator, TCL-1 (T-cell leukemia 1) (19), was applied to determine whether activation of Akt1 would be sufficient to overcome the inhibitory effects of Nogo. Fig.…”

Endotoxin tolerance: Selective alterations in gene expression and protection against lymphocyte death

“…In murine models of experimental sepsis, a reduction of lymphocyte apoptosis and necrosis by caspase or PARP inhibition respectively has been demonstrated to lead to improved survival rate (Szabo et al 1996;Hotchkiss and Nicholson 2006). Furthermore, clinical studies have demonstrated significant correlation between the severity of sepsis and the degree of apoptosis of circulating lymphocytes McDunn et al 2007) as well as PARP activation (Pacher et al 2005). The reduced expression in caspases as well as PARP afforded a protective effect against cell death, despite the fact that tolerant animals challenged with CLP produced high amounts of nitric oxide and superoxide.…”

Molecular biology of inflammation and sepsis: A primer*

“…PI3K/Akt has an effect in balancing Th1 vs. Th2 responses (50). Peptidemediated activation of Akt and extracellular regulated kinase signaling protects lymphocytes from numerous apoptotic stimuli both in vitro and in vivo (52). Peptidemediated activation of Akt and extracellular regulated kinase signaling protects lymphocytes from numerous apoptotic stimuli both in vitro and in vivo (52).…”