Age-Related Sympathetic Dysregulation is Associated with Glial Senescence in the Brainstem

Aging is an independent risk factor for cardiovascular diseases such as hypertension, myocardial infarction, stroke and heart diseases. Although the specific mechanisms for age‐related increase in the incidence of cardiovascular diseases are not yet known, accumulating evidence suggests that sympathetic nervous system (SNS) dysregulation plays a crucial role. Senescent cells accumulate in the brain with age and are implicated in the pathogenesis of neurodegenerative diseases, possibly through secretion of pro‐inflammatory cytokines, growth factors, and proteases through acquisition of senescence associated secretory phenotype (SASP). Our laboratory studies previously established that aging causes cellular senescence in the key brainstem regions important for sympathetic nervous system activity. In our current study, we investigated which cell type undergoes senescence in the brainstem of aged mice. Neurons are post‐mitotic and do not undergo senescence, whereas glial cells can undergo senescence. Hence, we hypothesized that aging induces glial senescence in the brainstem. To address this hypothesis, we used 28‐month old (n=4) and 4‐month old (n=5) C57BL/6J mice. The animals were sacrificed, and the brainstems were collected. The freshly isolated brainstem was enzymatically digested (45 minutes, 37°C) and filtered through a 30μm mesh to form a cell suspension. Neuron isolation kit from Miltenyi Biotec was used to isolate glial and neuronal enriched cell population from the brainstem cell suspension. RNA was extracted from these sorted cells and used for RT‐PCR analysis. Senescence was assessed using gene expression of cell cycle inhibitors and SASP factors. Data was analyzed by unpaired student’s t‐test and a p‐value less than 0.05 was considered statistically significant. We observed an increase in the gene expression of cell cycle inhibitors, p16, p21 and p53 in the glial cell fraction isolated from the brainstem of aged mice compared to its young counterparts. In addition, there was an increase in the mRNA levels of SASP factors such as the MCP1, TNF‐α, and IL‐1β suggesting that aging induces senescence in the glial cells of the brainstem. We were not able to obtain viable neurons for senescence analysis. Glial cells are known to play a supporting role in neuronal function through regulation of neurotransmission. Future studies will address glial cell specific mechanisms and understand how glia‐neuron crosstalk contributes to SNS dysregulation in aging. Support or Funding Information NIH‐HL148844 and RED account funds