Telomerase Enzyme Emerges as a Drug Target for Healing the Brain After Stroke

Every year, millions of people survive a stroke only to face a lifetime of disability that current medicine cannot reverse. Acute treatments such as intravenous thrombolysis and mechanical thrombectomy can rescue endangered brain tissue, but only within a narrow window of a few hours, and only a small proportion of patients reach the hospital in time. Once that window closes, recovery depends almost entirely on the brain’s own capacity to rewire itself, a process that is slow, incomplete, and poorly understood. Now, a team of researchers at Jinan University in China reports that an enzyme best known for its role in cellular aging, telomerase reverse transcriptase (TERT), acts as a master switch for neural repair after stroke, and that a small molecule derived from a traditional Chinese medicine can switch it on to restore lost function.

The study, published in the Journal of Advanced Research, addresses what the authors describe as a critically understudied area of medicine: tertiary stroke prevention. While primary prevention targets risk factors such as hypertension, diabetes, and smoking in people who have never had a stroke, and secondary prevention aims to stop recurrences in survivors through antiplatelet drugs and surgical interventions, tertiary prevention focuses on mitigating long-term disability and improving quality of life. Despite decades of progress in understanding how to protect neurons during the acute phase of ischemia, no clinically approved pharmacological intervention exists for promoting neural repair in the sub-acute and chronic phases that follow. This gap represents a substantial unmet medical need for the growing population of stroke survivors worldwide.

To investigate the biology of recovery, the researchers used a mouse photothrombosis model, in which cerebral vessels in the cortex are damaged by light-activated clotting to permanently block blood flow and cause a cortical infarction. A key advantage of this model is that it generates no penumbra, the salvageable tissue surrounding the infarct that complicates interpretation in other stroke models. Because the infarct is fixed and permanent, any recovery observed in the surrounding peri-infarct region can be attributed cleanly to spontaneous neural repair rather than to tissue rescue. Using laser speckle imaging, the team confirmed that the model successfully occluded cerebral blood flow and produced prominent cortical infarction visible by Nissl staining at day 14 after surgery.

The first major finding concerned where and when TERT appears in the recovering brain. Western blot analysis of peri-infarct tissue revealed that TERT protein expression rose significantly from day 7 after stroke, peaked at day 14, and then subsided, precisely matching the critical window of post-stroke spontaneous neural repair. To identify which brain cells were producing the enzyme, the researchers performed single-nucleus RNA sequencing on peri-infarct tissue collected at day 14, identifying nine major cell types by unsupervised clustering. TERT was expressed mainly in neurons, and immunofluorescent co-staining confirmed that roughly 78 percent of TERT in the peri-infarct cortex was detected in NeuN-positive neurons rather than in astrocytes, microglia, or endothelial cells. The pattern held in a second, independent stroke model, the middle cerebral artery occlusion model, where TERT was again upregulated at days 7 and 14 and predominantly localized to neurons.

Having established that TERT surges in peri-infarct neurons during recovery, the team asked what the enzyme was actually doing there. Although TERT is classically known for extending telomeres at chromosome ends, recent work has suggested it also regulates gene expression directly. Using Cleavage Under Targets and Tagmentation (CUT&Tag) sequencing, the researchers mapped TERT’s chromatin-binding sites across the whole genome in peri-infarct neurons and, in parallel, mapped the occupancy of Rpb1, a core subunit of RNA polymerase II that marks actively transcribing genes, along with the acetylated histone mark H3K27ac, which is correlated with active transcription. The analysis showed that most TERT-binding peaks were enriched at promoter regions, and that the set of TERT-bound promoters expanded by 27.8 percent in peri-infarct neurons compared with sham controls. Correlation with Rpb1 and H3K27ac signals indicated that TERT can act as both a positive and a negative transcriptional regulator in these neurons.

The identity of the genes whose promoters gained TERT binding was striking. Gene ontology analysis of the upregulated TERT-binding genes ranked terms such as regulation of axon regeneration, filopodium assembly, actin cytoskeleton organization, and positive regulation of neuron projection among the top biological processes, while known telomerase functions such as telomere maintenance appeared as expected positive controls. Even more intriguingly, motif enrichment analysis with HOMER revealed that the sequences bound by TERT best matched the recognition motif of cAMP response element-binding protein, or CREB, a transcription factor long regarded as a critical driver of neural plasticity, neurodevelopment, and repair. Known CREB-target genes involved in neural repair, including GAP43, EVL, NR4A4, and NRP2, were occupied by TERT at their promoters and showed higher transcriptional activity in peri-infarct neurons. When the researchers knocked down TERT in cultured cortical neurons subjected to an ischemia-induced neurite repair assay, the upregulated expression of these CREB-target genes was significantly abrogated, indicating that TERT is required for the transcriptional reprogramming that underlies neural repair.

To test whether boosting TERT could actively enhance recovery, the team delivered the enzyme into the brain using an intravenously injected, brain-tropic AAV PHP.eB vector carrying TERT under a neuron-specific promoter. Mice injected with the TERT overexpression vector showed markedly increased dendritic branching complexity and enriched mushroom and stubby spine morphologies in peri-infarct neurons, as revealed by Golgi-Cox staining and Sholl analysis, along with significantly enhanced axon and dendrite marker intensities measured by immunofluorescence for NEFM and PSD95. Western blotting confirmed upregulation of the repair-associated proteins GAP43, NEFM, and PSD95 in both the stroke-affected and contralateral hemispheres. Crucially, the structural repair translated into function: mice treated with TERT overexpression performed significantly better in the adhesive removal test of sensory function at day 28, and showed improved motor function on the grid-walk test and enhanced sensorimotor integration in the cylinder test from day 7 and day 14 onward, respectively.

Because gene therapy is an impractical near-term option for most patients, the researchers then turned to a pharmacological approach using cycloastragenol (CAG), a known TERT activator that is an active metabolite of Astragaloside IV isolated from the dried roots of Astragalus membranaceus, a legume used in traditional Chinese medicine as the herb Huangqi. The team administered CAG by oral gavage at a well-tolerated dose of 20 mg/kg from day 4 to day 14 after stroke, deliberately covering the recovery window while avoiding any confounding effect in the acute phase. CAG treatment did not change infarct size, confirming it acted on repair rather than tissue salvage, but it significantly increased TERT expression specifically in peri-infarct neurons. Golgi-Cox staining showed enhanced dendritic complexity and basal spine density, biotinylated dextran amine tracing revealed increased axon sprouting, and Western blots confirmed elevated levels of GAP43, NF160, PSD95, and the synaptic markers SYP and SYN. Behaviorally, CAG-treated mice showed significantly improved sensorimotor integration, fewer foot faults on the grid-walk, and shorter adhesive removal times. Conversely, when the researchers knocked down neuronal TERT with an AAV-delivered shRNA, both spontaneous recovery and the benefits of CAG treatment were abolished, demonstrating that endogenous neuronal TERT is necessary for the observed repair effects.

The study also uncovered an unexpected psychiatric benefit. Post-stroke depression affects an estimated 40 to 50 percent of stroke survivors and represents a major unmet therapeutic need. In the forced swim test, CAG-treated stroke mice showed significantly shortened immobility duration, and in the sucrose preference test they consumed significantly more sucrose, both indicating alleviation of depression-like behaviors, while an open-field test ruled out nonspecific psychostimulant effects. Surprisingly, neuronal TERT knockdown did not block the antidepressant effect, even though it abolished CAG-induced upregulation of brain-derived neurotrophic factor (BDNF) in the peri-infarct cortex, suggesting that BDNF is associated with the antidepressant action but that neuronal TERT may not be its key mediator. Using mass spectrometry-based phosphoproteomics, the researchers further traced the signaling pathway by which CAG activates TERT: kinase-substrate enrichment analysis pointed to the death-associated protein kinase DAPK1, and pharmacological inhibition of DAPK1 blocked CAG-induced TERT expression and the phosphorylation of the transcription factor STAT3 at its serine 727 residue, which binds to the mouse Tert promoter to drive transcription.

The translational profile of cycloastragenol adds to the excitement. The US Food and Drug Administration has designated CAG as generally recognized as safe, its oral bioavailability is approximately 25 percent, and its low molecular weight allows it to cross the blood-brain barrier. Clinical trials of CAG for anti-aging purposes have already demonstrated an excellent safety record, including a commercial health maintenance program spanning 7000 person-years of use with no adverse events attributed to the supplement, and preclinical studies across a broad dose range and experimental durations of 4 to 33 weeks have reported an overall favorable safety profile. Compared with AAV-mediated gene therapy, a small molecule offering transient, controllable upregulation of TERT may carry advantages in immunogenicity, cost, and dosing flexibility. The authors caution that important questions remain, including the precise mechanism of CAG’s antidepressant effect, the possible contributions of TERT in non-neuronal brain cells, and detailed pharmacokinetics in brain tissue. Nevertheless, the work provides a proof of concept that reactivating a telomerase enzyme in peri-infarct neurons, whether by gene delivery or by an ancient herbal compound, can rebuild neural circuits and restore function, positioning TERT as a promising therapeutic target for the recovery phase of stroke and potentially for other age-associated neurological diseases.

Subject of Research: The role of telomerase reverse transcriptase (TERT) in neural repair and functional recovery after ischemic stroke

Article Title: TERT is a therapeutic target for tertiary stroke prevention

Article References: TERT is a therapeutic target for tertiary stroke prevention. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: TERT, telomerase, ischemic stroke, neural repair, cycloastragenol, CREB, neuroplasticity, tertiary prevention, post-stroke depression, DAPK1, STAT3, gene therapy