Partial Cell Reprogramming Shields Aging Mouse Brains from Ischemic Stroke Damage

A four-week course of cyclic partial cellular reprogramming markedly reduced brain damage after stroke in aging mice, according to a new study in which researchers induced the expression of the four Yamanaka factors—Oct4, Sox2, Klf4, and c-Myc, collectively known as OSKM—in mice aged 12 to 18 months before surgically blocking a major cerebral artery. Forty-eight hours after permanent middle cerebral artery occlusion, the ischemic lesion occupied 31.5 percent of the affected hemisphere in wild-type animals but only 24.9 percent in transgenic mice whose reprogramming machinery had been switched on, a statistically significant difference that points to a genuine protective effect of the treatment.

The work addresses a stubborn gap in stroke medicine. Ischemic strokes, which account for roughly 87 percent of all cerebrovascular accidents, occur when a thrombus or atherosclerotic plaque cuts off blood supply to part of the brain, triggering the ischemic cascade of cell death, inflammation, oxidative stress, and demyelination. Aging is the primary risk factor for these events, and older patients consistently face poorer prognoses and weaker functional recovery than younger ones. The only therapeutic options currently available—thrombolytic agents such as tPA or mechanical thrombectomy—must be applied within a narrow time window, can provoke hemorrhage, fail to prevent long-term neurodegeneration, and may even worsen the initial injury by causing ischemia-reperfusion damage when blood flow suddenly returns.

Partial reprogramming rests on a famous foundation. When the four OSKM transcription factors are overexpressed, differentiated adult cells can be reverted to an embryonic-like pluripotent state, generating induced pluripotent stem cells. But pushing the process to completion in living animals is dangerous: in the first in vivo demonstration, continuous doxycycline administration in a reprogrammable mouse line produced teratomas, induced pluripotent stem cells circulating in the blood, and a sharply reduced life expectancy. The solution adopted by the field is cyclic, controlled expression—short pulses of the factors followed by withdrawal—which promotes repair and rejuvenation without complete dedifferentiation. This strategy has already shown benefits in skeletal muscle, liver, retina, skin, and cardiovascular tissue, and in mouse models of Alzheimer’s disease it improves the main pathological hallmarks.

What remained untested was whether such reprogramming could protect the aged brain against ischemia. Earlier studies had shown promise in young animals: seven days of continuous Yamanaka factor induction via intraventricular doxycycline perfusion after global ischemia facilitated functional recovery and enhanced neovascularization in mice only 8 to 16 weeks old, while viral delivery of OSKM in neonatal hypoxic-ischemic brain injury improved long-term memory and hippocampal neurogenesis. The elderly brain, however, accumulates molecular and cellular damage—mitochondrial dysfunction, cellular senescence, loss of proteostasis, DNA damage, and epigenetic alterations tracked by DNA methylation—that partial reprogramming is thought to reverse or mitigate while preserving cellular identity.

To probe this question, the team used the i4F-B transgenic mouse line, which carries a tetracycline-controlled transactivator inserted into the ubiquitously expressed Rosa26 locus together with a single-copy, doxycycline-inducible polycistronic cassette encoding the four murine reprogramming factors. Thirty C57BL/6 mice, 16 male and 14 female, received doxycycline at 2 milligrams per milliliter in drinking water in weekly cycles of three days on and four days off for four consecutive weeks before surgery. The animals were then randomly assigned to sham operations or to permanent middle cerebral artery occlusion performed by the Koizumi method, in which a silicon-coated monofilament is advanced through the internal carotid artery to the origin of the middle cerebral artery and left in place until euthanasia 48 hours later. Behavioral testing and microscopic examination were carried out by blinded investigators.

The first striking result came from the open field test in sham-operated animals. Reprogrammed mice traveled 21.96 meters on average, compared with 12.08 meters in wild-type littermates, and moved at an average speed of 0.036 versus 0.020 meters per second. They also spent far less time motionless—173.5 seconds against 340 seconds. Notably, the time spent in the center of the arena, a standard index of anxiety-like behavior, did not differ between genotypes, indicating that the hyperactive phenotype was not driven by stress. Immunofluorescence confirmed that Oct4 and Klf4 were expressed in neurons, astrocytes, microglia, and oligodendrocytes—the first description of Yamanaka factor overexpression in oligodendrocytes and microglia in vivo—yet the induction changed no cell population densities under normal conditions, suggesting improved function of existing cells rather than altered neurogenesis or gliogenesis.

After ischemia, the histological and behavioral picture diverged sharply between genotypes. Six hours after occlusion, both groups scored similarly on a seven-point neurological scale, confirming successful induction of the stroke model. But by 24 hours the reprogrammed group scored 2.62 on the ischemic damage index against 1.9 in wild-type mice, and by 48 hours the gap widened to 2.68 versus 1.41, a difference the authors interpret as a partial improvement in neurological outcome. On the tightrope test, which probes forelimb coordination and grip strength—the functions most affected in this occlusion model—reprogrammed mice scored 2.75 at 48 hours compared with 0.4 in wild-type animals. The beam walking test, which assesses global locomotion across all four limbs, showed no significant differences, indicating that the benefit of OSKM induction is task dependent and tracks the cortical territory damaged by the occlusion.

Underlying these behavioral changes were clear histological protections. Neuronal density in the parietal cortex, near 300 cells per square millimeter in both sham groups, fell to 207.7 cells per square millimeter in ischemic wild-type mice but remained at sham levels in reprogrammed animals. The glial response told a parallel story: astrocyte density in the ischemic penumbra surged from 228 to 445 cells per square millimeter in wild-type mice after occlusion, while reprogrammed mice showed no significant increase over their sham counterparts. Microglial density, measured with Iba1 staining, did not differ between groups, consistent with the knowledge that the microglial response to ischemia peaks within 24 hours, earlier than the 48-hour analysis window.

Myelin preservation was equally impressive. Black-Gold II staining revealed a drastic drop in myelinated area to 61.7 percent in ischemic wild-type cortex, whereas reprogrammed ischemic mice showed no significant loss relative to sham controls, with values around 108 percent. Immunostaining refined the picture: levels of myelin basic protein were similar across all groups, but myelin-associated glycoprotein, or MAG, fell to 76.3 percent in ischemic wild-type mice while remaining stable in the reprogrammed group. Because MAG sits distally on periaxonal processes and anchors the oligodendrocyte membrane to the axon, its selective loss is read as an early sign of disrupted axon-glia integrity. In the damaged cortex, total oligodendrocyte density rose to 497 cells per square millimeter in reprogrammed mice versus 338 in wild-type, and oligodendrocyte precursor cells increased to 80.02 per square millimeter from 51.17 in sham reprogrammed animals, suggesting enhanced recruitment of precursors resembling the responses of younger brains.

The authors caution that several limitations frame these findings. The sample size was not designed for statistically powered sex-specific analysis, the observations cover only the acute 48-hour phase after ischemia, and doxycycline itself can alter gut microbiota, exert neuroprotective anti-inflammatory effects, impair mitochondrial function, and change baseline gene expression—although uniform exposure across both genotypes means the observed phenotypes should reflect genetic activation rather than the antibiotic alone. The mechanism also remains unresolved: the authors speculate that reprogramming might shift neuronal metabolism from oxidative phosphorylation toward glycolysis or ketogenesis, reducing oxygen dependence, and that reprogrammed endothelial cells might strengthen the aging blood-brain barrier, but neither hypothesis was directly tested. What the data do establish is that four weeks of cyclic OSKM expression in aging mice is associated with preserved neuronal viability, maintained myelin integrity, a dampened astrocytic response, reduced tissue damage, and improved performance on forelimb-sensitive motor tasks after ischemic stroke—a result that, if it can be extended beyond the acute phase and toward translational delivery strategies, suggests partial reprogramming may help blunt the impact of the disease for which age is the greatest risk factor.

Subject of Research: Partial in vivo cellular reprogramming with Yamanaka factors as a neuroprotective intervention against ischemic stroke in aging mice

Article Title: In Vivo Partial Cell Reprogramming With Yamanaka Factors Reduced Ischemic Brain Damage in Aging Mice

Article References: Mallavibarrena, P. R., Martín‐López, G., Rodríguez‐Morales, J., Ávila, J., Hernández, F., & Pérez‐Álvarez, M. J. (2026). In Vivo Partial Cell Reprogramming With Yamanaka Factors Reduced Ischemic Brain Damage in Aging Mice. Aging Cell, 25(11), Article e70776. https://doi.org/10.1111/acel.70776

Image Credits: AI Generated

DOI: 10.1111/acel.70776

Keywords: partial reprogramming, Yamanaka factors, OSKM, ischemic stroke, aging brain, neuroprotection, myelin preservation, oligodendrocytes, middle cerebral artery occlusion, doxycycline, cellular rejuvenation, mouse model