The effect of ubiquitin on immune response after controlled cortical impact injury

Extracellular Ubiquitin Enhances Autophagy and Inhibits Mitochondrial Apoptosis Pathway to Protect Neurons Against Spinal Cord Ischemic Injury via CXCR4

OBJECTIVE

Neuronal apoptosis is considered to be a critical process in spinal cord injury (SCI). Despite growing evidence of the antiapoptotic, anti-inflammatory, and modulation of ischemic injury tolerance effects of extracellular ubiquitin (eUb), existing studies have paid less attention to the impact of eUb in neurological injury disorders, particularly in SCI. This study aimed to investigate whether eUb can play a protective role in neurons, both in vitro and in vivo, and explores the underlying mechanisms.

METHODS

By utilizing an oxygen glucose deprivation cellular model and a SCI rat model, we firstly investigated the therapeutic effects of eUb on SCI and further explored its effects on neuronal autophagy and mitochondria-dependent apoptosis-related indicators, as well as the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mechanical target of rapamycin (mTOR) signaling pathway.

RESULTS

In the SCI models both in vivo and in vitro, early intervention with eUb enhanced neuronal autophagy and inhibited mitochondrial apoptotic pathways, significantly mitigating SCI. Further studies had shown that this protective effect of eUb was mediated through its receptor, CXC chemokine receptor type 4 (CXCR4). Additionally, eUb-enhanced autophagy and antiapoptotic effects were possibly associated with inhibiting the PI3K/Akt/mTOR pathway.

CONCLUSION

In summary, the study demonstrates that early eUb intervention can enhance autophagy and inhibit mitochondrial apoptotic pathways via CXCR4, protecting neurons and promoting SCI repair.

Almost 50 Years of Monomeric Extracellular Ubiquitin (eUb)

Monomeric ubiquitin (Ub) is a 76-amino-acid highly conserved protein found in eukaryotes. The biological activity of Ub first described in the 1970s was extracellular, but it quickly gained relevance due to its intracellular role, i.e., post-translational modification of intracellular proteins (ubiquitination) that regulate numerous eukaryotic cellular processes. In the following years, the extracellular role of Ub was relegated to the background, until a correlation between higher survival rate and increased serum Ub concentrations in patients with sepsis and burns was observed. Although the mechanism of action (MoA) of extracellular ubiquitin (eUb) is not yet well understood, further studies have shown that it may ameliorate the inflammatory response in tissue injury and multiple sclerosis diseases. These observations, compounded with the high stability and low immunogenicity of eUb due to its high conservation in eukaryotes, have made this small protein a relevant candidate for biotherapeutic development. Here, we review the in vitro and in vivo effects of eUb on immunologic, cardiovascular, and nervous systems, and discuss the potential MoAs of eUb as an anti-inflammatory, antimicrobial, and cardio- and brain-protective agent.

Effects of exogenous ubiquitin in a polytrauma model with blunt chest trauma

OBJECTIVE

To determine whether treatment with the CXC chemokine receptor 4 agonist ubiquitin results in beneficial effects in a polytrauma model consisting of bilateral femur fractures plus blunt chest trauma (Injury Severity Score 18-25).

DESIGN

Treatment study.

SETTING

Research laboratory.

SUBJECTS

Seventeen Yorkshire pigs.

INTERVENTIONS

Intravenous injection of 1.5 mg/kg ubiquitin or albumin (control) at 60 mins after polytrauma.

MEASUREMENTS AND MAIN RESULTS

Anesthetized, mechanically ventilated pigs underwent polytrauma, followed by a simulated 60-min shock phase. At the end of the shock phase, ubiquitin or albumin were administered and animals were resuscitated to a mean arterial blood pressure of 70 mm Hg until t=420 mins. After intravenous ubiquitin, ubiquitin plasma concentrations increased 16-fold to 2870±1015 ng/mL at t=90 mins and decreased with t1/2=60 mins. Endogenous plasma ubiquitin increased two-fold in the albumin group with peak levels of 359±210 ng/mL. Plasma levels of the cognate CXC chemokine receptor 4 ligand stromal cell-derived factor-1α were unchanged in both groups. Ubiquitin treatment reduced arterial lactate levels and prevented a continuous decrease in arterial oxygenation, which occurred in the albumin group during resuscitation. Wet weight to dry weight ratios of the lung contralateral from the injury, heart, spleen and jejunum were lower with ubiquitin. With ubiquitin treatment, tissue levels of Interleukin-8, Interleukin-10, Tumor Necrosis Factor α, and stromal cell-derived factor-1α were reduced in the injured lung and of Interleukin-8 in the contralateral lung, respectively.

CONCLUSIONS

Administration of exogenous ubiquitin modulates the local inflammatory response, improves resuscitation, reduces fluid shifts into tissues, and preserves arterial oxygenation after blunt polytrauma with lung injury. This study further supports the notion that ubiquitin is a promising protein therapeutic and implies CXC chemokine receptor 4 as a drug target after polytrauma.