Mice live longer with nasal gene therapy

By Bhavana KunkalikarReviewed by Danielle Ellis, B.Sc.May 17 2022

In a recent study published in the Proceedings of the National Academy of Sciences journal, researchers assessed the efficiency of a novel intranasal and injectable therapy in improving life expectancy.

The association of increasing age with the decrease in telomere repeat elements found at the end of chromosomes has been well documented. This reinforces the need to develop effective methods of mitigating the effect of aging on human well-being. 

Study: New intranasal and injectable gene therapy for healthy life extension. ​​​​​​​Image Credit: nobeastsofierce / Shutterstock

About the study

In the present study, researchers determined the impact of a high-capacity cytomegalovirus vector (CMV) on factors like follistatin (FST) and telomerase reverse transcriptase (TERT) that protect against the influence of aging on human health.

The team developed a mouse CMV (MCMV) vector that expressed luciferase as a reporter gene (MCMV_Luc) in order to surveil MCMV infection and its replication in culture as well as in a mouse model. Replicated MCMV_Luc along with its parental virus was used in this study as a wild-type MCMV virus inoculation (WT) or viral vector control. The team also generated recombinant MCMV vectors that expressed FLAG-tagged genes telomerase reverse transcriptase (TERT) and FST (MCMV_TERT and MCMV_FST).   

Furthermore, the team fused the mouse TERT with the FLAG-tag at the C-terminus using two intermediate amino acids, namely arginine and threonine. The expression kinetics of the target protein and the therapeutic effectiveness of CMV was determined by evaluating the levels of TERT in the blood samples of eight-month-old mice over a span of a month post-treatment.

The extension of life after treatment was evaluated by administering seven out of nine groups of aged female mice with mock treatment intraperitoneally (IP), WT-treated intranasally (IN) (WT-IN), WT-IP, MCMV_TERT-IN, MCMV_TERT-IP, MCMV_FST-IN, and MCMV_FST-IP, respectively. The treatment was first started in 18-month-old mice. The team sacrificed one mouse in each group at 24 months to perform tissue analysis while the rest of the mice were monitored for changes in their physiology until their natural death.

Furthermore, the length of telomeres in kidneys and muscle tissues was determined, and comparisons were drawn between those in different mice groups using quantitative fluorescence in situ hybridization (Q-FISH). The team also estimated the telomere length observed in the skeletal muscles of mice treated with TERT. The telomere length of various organs was also evaluated using real-time quantitative polymerase chain reaction (qPCR).    

Results

The study results showed that the FLAG-tagged genes MCMV_TERT and MCMV_FST replicated to a degree comparable to that of MCMV_Luc (WT) in the fibroblast cells in mice and in vivo. The expression of TERT protein when administered IN or IP was its highest seven days after treatment before gradually reducing to its basal level on day 25. This indicated that the vector was able to deliver proteins in an in vivo environment. Analysis of FST and TERT messenger ribonucleic acids (mRNAs) and proteins in blood and tissue samples obtained from treated animals.

Analysis of the impact of treatment on life extension showed that the WT and mock control mice succumbed after a median duration of 26.7, 26.5, and 26.4 months. The median age of death in the MCMV_FST-treated and the MCMV_TERT-treated mice was 35.1 and 37.5 months, respectively. The team noted that the longest lifespan was observed in MCMV_TERT-treated mice at 41.2 months, while that in the MCMV_FST-treated mice was 38.0 months. The team remarked that CMV therapy was comparable in effectiveness irrespective of the route of inoculation, which suggested that the expression of genes was not significantly impacted by the interaction of the vector with the immune system.

The results of the Q-FISH method showed an increase of 3.1-fold in the length of telomeres in the kidneys of TERT-treated mice in comparison to the untreated mice controls. Moreover, the number of telomeres observed in the kidneys of mice treated with TERT was significantly higher than those in the untreated mice or those treated with WT. Notably, no substantial changes were found in FST-treated or the WT-treated subjects which suggested the efficiency of TERT in the TERT-treated mice.

The team also observed that the telomere length in the muscular tissues of the TERT-treated mice increased by almost three times as compared to those in the untreated subjects. In contrast, there was no substantial increase in the telomere length in the FST- or the WT-treated mice. Moreover, qPCR showed no variation in the length of the telomeres in the different tissues of mice treated with TERT. The team noted that the relative telomere length in the brain, heart, lung, liver, and kidney in 24-month-old MCMV_TERT-treated mice was almost three times more than that in untreated mice of the same age. 

Conclusion

Overall, the study findings showed the importance of investigating the impact of CMV TERT and FST vector usage against conditions related to aging, such as chronic inflammatory conditions, sarcopenia, type 2 diabetes, and heart diseases.