Obesity‐Induced Sympathoexcitation is Associated with Glial Senescence in the Brainstem

Abstract

Previous studies from our laboratory showed that high fat diet‐induced obesity causes cellular senescence in the key brainstem region, the rostral ventrolateral medulla which is critical for the tonic and reflex control of sympathetic nervous system. Cellular senescence is characterized by a state of irreversible growth arrest and senescence‐associated secretory phenotype (SASP) in proliferating cells. In the current study, we wanted to investigate which cell type undergoes senescence in the brainstem in obesity. Neurons are post‐mitotic and do not undergo senescence, whereas glial cells can undergo senescence. Hence we hypothesized that obesity induces glial senescence in the brainstem. To address this hypothesis, 2‐month old C57BL/6J mice were fed with high fat diet (60% fat; n=5) and chow diet (10% fat; n=5) for 16 weeks. The animals were sacrificed at the end of the experiment, and their brains were collected for further processing. 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. 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, p21 and p53 in the glial cell fraction isolated from the brainstem of obese mice compared to its lean counterparts. In addition, there was an increase in the mRNA levels of SASP factors such as the IL‐6 and MCP1 suggesting that obesity induces glial senescence in 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 sympathetic nerve overactivity in obesity.Support or Funding InformationNIH‐HL148844 and RED account funds