Development of a Novel Animal Model for Spinal Cord Injury with Sepsis

Abstract This timely proposal is in response to the recent NIH R21 funding opportunity announcement PA-21-219. Sepsis is a predominant life-threatening secondary complication following traumatic spinal cord injury (SCI). Several predisposing factors such as polytrauma, prolonged/repeated hospital stay, pressure ulcer, and indwelling catheters make SCI patients more susceptible to microbial infection that can lead to sepsis. Sepsis is a leading cause of death after spinal trauma and is associated with poor functional outcomes among survivors. Depending on the onset, there are two sepsis types. Sepsis diagnosed within 48hr of initial injury is termed “primary” sepsis, and when its onset occurs after 48hr, it is known as “secondary” sepsis. Though sepsis with SCI is a serious condition leading to diminished life expectancy and quality of life, this combined medical issue has not been well studied. This is mainly due to lack of an appropriate animal model. Accordingly, this research proposal is to develop and validate a novel clinically relevant rodent model that closely mimics the long-term dysfunction of survivors of sepsis following traumatic spinal cord injury. Previously, our team developed a clinically relevant rodent sepsis model consisting of polymicrobial abdominal sepsis by cecal slurry (CS) injection followed by a delayed but repeated ICU-like resuscitation procedure with fluids and antibiotics; this refined model allows us to investigate long-term physical dysfunction such as muscle weakness among sepsis survivors. Our main approach is to combine this long-term sepsis survivor model with our existing rat spinal contusion model to mimic either “primary” (Aim 1) or “secondary” (Aim 2) sepsis following SCI. Our central hypothesis is that the cumulative effects of sepsis plus SCI will impair spontaneous motor recovery, limit spinal cord tissue sparing, exacerbate skeletal muscle weakness, and increase mortality. Two specific Aims are designed to test this hypothesis. In Aim 1, we will induce sepsis immediately after SCI to mimic “primary” sepsis by CS injection followed by ICU-like resuscitation initiated at 8 hrs. To mimic “secondary” sepsis, in Aim 2, we will induce sepsis at 6 weeks after SCI by CS injection and resuscitation initiated at 8hrs. SCI animals in Aim 1 will undergo weekly locomotor testing for 6 weeks and in Aim 2, for a total of 12 weeks (6 weeks before sepsis induction and 6 weeks after) to assess spontaneous recovery. Horizontal ladder and catwalk will be performed at 6 weeks for Aim 1 and at 6 and 12 weeks for Aim 2. After final locomotor assessments, survivors will be subjected to ex vivo muscle force testing, histological examination, and mitochondrial function analyses to assess muscle weakness. Spinal cord tissue will be used for quantitative histology of spared gray and white matter as well as lesion volume that will be correlated with locomotor recovery. Blood, spinal cord muscle and spleen tissues will be collected to assess inflammatory markers. Successful development of this model will allow us to investigate detailed molecular/physiological mechanisms of sepsis following SCI, with a long-term goal of developing therapeutic strategies to improve quality of life in the afflicted population.