Physiologic, ventilatory, and CNS transcriptomic response to chronic hypercapnia in goats

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PROJECT SUMMARY Chronic obstructive pulmonary disease (COPD) affects 24 million US adults and over 1 billion people worldwide. COPD patients often present with chronic hypercapnia (CH, elevated CO2 in the body), with severity of CH increasing as the disease progresses. COPD is also marked by acute “attacks”, known as acute-on-chronic exacerbations, further increasing the level of hypercapnia within the body. Some COPD patients demonstrate tolerable, adaptive responses to the exacerbations, whereas others are prone to life-threatening severe hypercapnia and potentially fatal cardiorespiratory dysfunction. The severity of CH may be an important factor in setting the threshold of susceptibility to adaptive versus pathophysiologic responses. Indeed, our previous findings have shown goats chronically exposed to mild CH (6% inspired CO2, InCO2) demonstrated adaptations across multiple physiologic systems and tolerated further acute increases in InCO2 to 7 and 8% CO2. In contrast, in a preliminary study on one goat, chronically increasing InCO2 from mild to moderate levels (8% InCO2), resulted in pathophysiologic responses and the inability to compensate for acute further increases in InCO2 to 9% and 10%. The molecular underpinnings governing the protective/adaptive responses to chronic mild CH or pathophysiologic/maladaptive responses to chronic moderate CH are unclear. Accordingly, the overall goal of this proposal is to gain insight into CH-dependent molecular mechanisms which potentially underly both the protective/adaptive (AIM 1) and pathophysiologic/maladaptive physiologic (AIM 2) responses to increased CO2 challenges. For AIM 1 I will expose adult goats to 14 days (d) of room air (Group 1) or mild CH (Group 2). For AIM 2, I will expose goats to 7d of mild CH (6% CO2) followed by 7d of moderate CH (8% CO2) (Group 3). I will measure physiological/pathophysiologic responses across multiple physiologic systems during steady-state conditions and during acute CO2 challenges. Goats will be euthanized after these studies and I will extract tissue from key brainstem cardiorespiratory nuclei and utilize bulk-tissue mRNA sequencing (btRNA-Seq) to identify differentially expressed genes induced by both mild CH and moderate CH. I will use Ingenuity Pathway Analysis to identify canonical pathways and functional gene networks that are significantly altered during mild CH (6% CO2) alone, or 7d mild CH followed by 7d of moderate CH (8% CO2). Combining broad, unbiased techniques (btRNA-Seq) and physiologic studies will provide novel insights into the molecular mechanisms regulating cardiorespiratory control networks during CH. Further, results will yield information that will be critical in understanding the effect CH has on the physiologic dysfunction observed in outpatient clinics and ICUs. The training plan outlined in this proposal will provide me with the expertise needed to conduct physiologic experiments, molecular biology techniques, and bioinformatic analyses required for the proposed studies.