Gastrointestinal disease is prevalent and broad, manifesting itself in a variety of ways, including inflammation, fibrosis, infection, and cancer. However, historically, diagnostic technologies have exhibited limitations, especially with regard to diagnostic uncertainty. Despite development of newly emerging technologies such as optoacoustic imaging, many recent advancements have focused on improving upon pre-existing modalities such as ultrasound, computed tomography, magnetic resonance imaging, and endoscopy. These advancements include utilization of machine learning models, biomarkers, new technological applications such as diffusion weighted imaging, and new techniques such as transrectal ultrasound. This review discusses assessment of disease processes using imaging strategies for the detection and monitoring of inflammation, fibrosis, and cancer in the context of gastrointestinal disease. Specifically, we include ulcerative colitis, Crohn’s disease, diverticulitis, celiac disease, graft vs. host disease, intestinal fibrosis, colorectal stricture, gastric cancer, and colorectal cancer. We address some of the most recent and promising advancements for improvement of gastrointestinal imaging, including unique discussions of such advancements with regard to imaging of fibrosis and differentiation between similar disease processes.

Background: Phosphofructo‐2‐kinase/fructose‐2,6‐bisphosphatase (PFK‐2) is a critical glycolytic regulator responsible for upregulation of glycolysis in response to insulin and adrenergic signaling. PFKFB2, the cardiac isoform of PFK‐2, is degraded in the heart in the absence of insulin signaling, contributing to diabetes‐induced cardiac metabolic inflexibility. However, previous studies have not examined how the loss of PFKFB2 affects global cardiac metabolism and function. Methods and Results: To address this, we have generated a mouse model with a cardiomyocyte‐specific knockout of PFKFB2 (cKO). Using 9‐month‐old cKO and control mice, we characterized the impacts of PFKFB2 on cardiac metabolism, function, and electrophysiology. cKO mice have a shortened life span of 9 months. Metabolically, cKO mice are characterized by increased glycolytic enzyme abundance and pyruvate dehydrogenase activity, as well as decreased mitochondrial abundance and beta oxidation, suggesting a shift toward glucose metabolism. This was supported by a decrease in the ratio of palmitoyl carnitine to pyruvate‐dependent mitochondrial respiration in cKO relative to control animals. Metabolomic, proteomic, and Western blot data support the activation of ancillary glucose metabolism, including pentose phosphate and hexosamine biosynthesis pathways. Physiologically, cKO animals exhibited impaired systolic function and left ventricular dilation, represented by reduced fractional shortening and increased left ventricular internal diameter, respectively. This was accompanied by electrophysiological alterations including increased QT interval and other metrics of delayed ventricular conduction. Conclusions: Loss of PFKFB2 results in metabolic remodeling marked by cardiac ancillary pathway activation. This could delineate an underpinning of pathologic changes to mechanical and electrical function in the heart.

Background: The heart’s constant energy demands make metabolic flexibility critical to its function as nutrient availability varies. The enzyme phosphofructokinase‐2/fructose 2,6‐bisphosphatase (PFKFB2) contributes to this flexibility by acting as a positive or negative regulator of cardiac glycolysis. We have previously shown that PFKFB2 is degraded in the diabetic heart and that a cardiac‐specific PFKFB2 knockout (cKO) impacts ancillary glucose pathways and mitochondrial substrate preference. Therefore, defining PFKFB2’s role in mitochondrial metabolic flexibility is paramount to understanding both metabolic homeostasis and metabolic syndromes. Further, it is unknown how PFKFB2 loss impacts the heart’s response to acute stress. Here, we examined how cardiac mitochondrial flexibility and the posttranslational modification O‐GlcNAcylation are affected in cKO mice in response to fasting or pharmacologic stimulation. Methods: cKO and litter‐matched controls were euthanized in the fed or fasted (12 hours) states, with or without a 20‐minute stimulant stress of caffeine and epinephrine. Mitochondrial respiration, metabolomics, and changes to systemic glucose homeostasis were evaluated. Results: cKO mice had moderate impairment in mitochondrial metabolic flexibility, affecting downstream glucose oxidation, respiration, and carnitine palmitoyl transferase 1 activity. O‐GlcNAcylation, a product of ancillary glucose metabolism, was upregulated in cKO hearts in the fed state, but this was ameliorated in the fasted state. Furthermore, metabolic remodeling in response to PFKFB2 loss was sufficient to impact circulating glucose in fasted and stressed states. Conclusions: PFKFB2 is essential for fed‐to‐fasted changes in cardiac metabolism and plays an important regulatory role in protein O‐GlcNAcylation. Its loss also affects systemic glucose homeostasis under stressed conditions.

Background: The cardiac isoform of phosphofructokinase-2/fructose 2,6-bisphosphatase (PFKFB2) is the heart’s strongest glycolytic regulator but is degraded in the absence of insulin signaling. This makes PFKFB2 loss critical to understand in metabolic heart disease, of which impaired insulin signaling is a hallmark. Prolongation of the QT interval, risk of arrhythmia, and sudden cardiac death are also augmented in metabolic heart disease, raising a question as to whether potential crosstalk between glycolytic dysregulation and electrophysiological dysfunction exists. Methods: We therefore assessed the impact of PFKFB2 loss on cardiac electrophysiology using a cardiomyocyte-specific PFKFB2 knockout mouse model (cKO) and litter-matched controls (CON). To do so, we employed electrocardiography in the fed state and following 12 hours of fasting, examining physiology both at baseline and in the presence of an acute stimulant stress. To further investigate the arrhythmia mechanism, we used patch-clamp electrophysiology and IonOptix Ca ²⁺ transient measurements in ventricular cardiomyocytes isolated from CON and cKO hearts. Results: The hearts of cKO mice exhibited prolonged repolarization, marked by QT and action potential duration prolongations. This occurred with impaired Ca ²⁺ reuptake and increased spontaneous Ca ²⁺ release events in ventricular cardiomyocytes. Ultimately, these changes culminated in ventricular tachyarrhythmia in cKO mice, which was enhanced in the fed relative to the fasted state. Conclusion: These data suggest that in the presence of sufficient glucose availability, cardiac glycolytic dysregulation at the phosphofructokinase nexus is sufficient to promote cardiac electrophysiological instability. Clinical Perspective: What is Known: Metabolic heart diseases, such as heart failure with preserved ejection fraction and diabetic cardiomyopathy, are associated with heightened risks of arrhythmogenesis and sudden cardiac death. What the Study Adds: Here, we show for the first time that PFKFB2 is decreased in human hearts with heart failure with preserved ejection fraction. Furthermore, we show that loss of cardiac PFKFB2 is sufficient to promote impaired ventricular repolarization at baseline and ventricular tachyarrhythmia upon stress test. This identifies PFKFB2 stabilization and activation as key potential targets in conferring electrophysiological stability in metabolic heart disease.

A growing body of work has recently linked ventral tegmental area (VTA) dopamine neuron dysfunction to Alzheimer′s disease (AD). Work in AD mouse models suggests that VTA dopamine neurons are intrinsically hyperexcitable, yet release less dopamine and exhibit disrupted downstream signaling. Significant focus has been placed on describing dopamine release in projection regions; however, dopamine neurons somatodendritically integrate vast synaptic input, altering action potential output and ultimately determining neurotransmitter release. Synaptic transmission is broadly disrupted in AD, but it is not known to what extent excitatory and inhibitory inputs to the VTA are altered. Here we describe enhanced synaptic excitation in dopamine neurons in the amyloid + tau-driven 3xTg-AD mouse model. Patch-clamp electrophysiology experiments revealed enhanced AMPAR-mediated excitatory input in a subset of perisomatic connections. In contrast, GABAAR-mediated inhibition was decreased as a function of dendritic atrophy, determined by single neuron reconstructions. We also detected elevated protein kinase C (PKC) substrate levels in the midbrain, and pharmacological experiments suggested that the strengthened excitation depends on elevated PKC activity. Additionally, postsynaptic AMPA receptor conductance was enhanced and displayed diminished ability to induce plasticity (long-term depression), but this was not dependent upon increased AMPA receptor expression. Morphologically detailed biophysical modeling predicted that synaptic changes, in combination with altered dendritic morphology and intrinsic hypersensitivity, produce increased spontaneous firing rates and a steeper input-output relationship in 3xTg-AD neurons. The results argue against a uniform decrease in synaptic connectivity across the brain in AD, and sheds light on the involvement of deep brain circuits. AD pathology is therefore associated with increased sensitivity of single dopamine neurons, which may help to maintain phasic dopamine signaling in early stages of degeneration.

As a bifunctional enzyme, phosphofructokinase-2/fructose 2,6-bisphosphatase (PFKFB or PFK-2) produces and degrades fructose-2,6-bisphosphate (Fru-2,6-P₂). Because Fru-2,6-P₂ is a strong allosteric activator of glycolysis, PFKFB is critical to glycolytic regulation. Four isoenzymes of PFKFB have been identified (PFKFB1-4). PFKFB2 is considered the cardiac isoenzyme and is distinct among the isoforms because of its complex regulation via multi-site phosphorylation. It plays critical roles in cardiac physiological responses to stress, with its loss a key driver of pathophysiology in metabolic cardiac diseases. However, PFKFB2 is also expressed in multiple additional tissues and is involved in noncardiac pathologies including cancer. Therefore, an ongoing area of research is the regulation of PFKFB2 activity and abundance. Here, we review the history and present knowledge of the structure, function, tissue distribution, and roles of PFKFB2 in physiology, stress response, and pathophysiology, both in the heart and other tissues systemically.