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Background: During acute hypoxia, Thehuman brainemploys complex regulatory mechanisms to compensate for high O 2 demand and low O 2 blood saturation. High hemoglobin-oxygen (Hb-O 2 ) affinity improves arterial oxygen saturation (S a O 2 ) in low oxygen environments providing a potential physiologic benefit in humans. However, the impact of high Hb-O 2 affinity on cerebral blood flow (CBF) and cerebral tissue oxygenation (S t O 2 ) has yet to be examined. This work aimed to determine the influence of an acute increase in Hb-O 2 affinity from Etavopivat, a selective red blood cell pyruvate kinase activator, on CBF regulation and S t O 2 during handgrip exercise in normoxia and hypoxia. Methods: 16 healthy adults (31±8 yr, 5 females) completed two visits; before and after Etavopivat (400 mg daily, 7 days) administration,. Each visit included graded handgrip (~3 min stages each) exercise (rest, 10% maximal voluntary contraction (MVC), 20% MVC) while participants inspired normoxic (NORM, 21% O 2 ), moderate (MH, 15% O 2 ), and severe (SH, 10% O 2 ) hypoxic gas mixtures. Hb-O 2 binding affinity (P 50 ), was measured using dual-wavelength spectrophotometry (pH~7.4 and 37ºC). Blood sampling through catheterization of the non-exercising arm measured S a O 2 . CBF was approximated by the peak middle cerebral artery velocity, measured with a 2MHz transcranial doppler ultrasound through the transtemporal window. S t O 2 was measured using frequency-domain near infrared spectroscopy of the frontal cortex. CBF and S t O 2 between visits were compared using separate two-way RM ANOVA models to determine the effects of Etavopivat [before (baseline) or after 7d Etavopivat exposure (post)] and exercise intensity [rest, 10% MVC, 20% MVC] for each inspirate. Results: P 50 was reduced after Etavopivat exposure (Baseline: 28.6±1.6 mmHg, Etavo: 24.8±1.3, P <0.001) without impacting hematocrit ( P =0.97). S a O 2 was higher following Etavopivat exposure during each inspirate ( P <0.001 for each). There was no significant effect of handgrip exercise on CBF or S t O 2 within any inspirate. Cerebral S t O 2 was higher during each inspirate (all P <0.002)– NORM (Baseline: 65.3±12.3%, Post: 68.8±9.8%), MH (Baseline: 61.0±11.7 %, Post: 66.1±10.5%) and SH (Baseline: 47.7±13.5%, Post: 56.6±11.5%). In addition, CBF was increased during each inspirate (all P <0.001)– NORM (Baseline: 62.2±12.2 cm/s, Post: 69.2±12.5 cm/s), MH (Baseline: 60.8±13.1 cm/s, Post: 67.9±12.3 cm/s) and SH (Baseline: 69.8±16.3 cm/s, Post: 79.2±18.0 cm/s). Conclusion: The acute pharmacological induction of high Hb-O 2 affinity leads to increased CBF and cerebral S t O 2 during acute hypoxic exposure in conditions of mild muscular exertion. Whether the improvement of cerebral S t O 2 is associated increased S a O 2 or CBF (or both) is unclear. These findings are the first to investigate the complex determinants of cerebral S t O 2 as a function of an acute increase in Hb-O 2 affinity. These improvements in S t O 2 during hypoxic exposure may lead to a host of theoretical benefits such as improved hypoxia tolerance, and mitigated decrements in cognitive function during hypoxic exposure. This study was funded by Forma Therapeutics Inc, which was acquired by Novo Nordisk on October 14, 2022, Novo Nordisk A/S. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Dynamic cerebral autoregulation (CA) refers to the brain's ability to maintain stable cerebral blood flow despite fluctuations in blood pressure (BP). Impaired CA has been associated with cardiovascular disease severity and cognitive decline. On the other hand, enhanced cardiorespiratory fitness appears to be protective against both cerebrovascular dysregulation and cognitive decline, with an unclear link between the two. However, among individuals with cardiovascular disease, the impact of exercise-based cardiac rehabilitation (CR) on CA remains unclear. Therefore, the aim of this study was to test the hypothesis that a 12-week CR program would improve dynamic CA in adults with CVD. To address this question, data were collected from 14 patients enrolled in the Mayo Clinic CR program following a cardiac-related hospital admission (age: 43-70 yrs; n=3 females), which included moderate-high intensity aerobic exercise 3 times/week for 12-weeks. Continuous measures of middle cerebral artery velocity (MCAv; transcranial doppler) and finger BP (photoplethysmography) were obtained during 3-minutes of rest and a 3-minute sit-to-stand protocol (0.025Hz frequency) pre- and post the CR program. Transfer function analyses were used to provide an index of dynamic CA. BP-MCAv coherence in the low frequency (LF) and very low frequency (vLF) domains at rest were not different pre- and post- CR (LF: 0.48±0.19 vs 0.43±0.16; P=0.54; vLF: 0.51±0.12 vs 0.47±0.16; P=0.14). Similarly, gain and phase values at rest were not different pre- and post- CR (gain LF: 0.66±0.37 vs 0.58±0.33; P=0.16; vLF: 0.87±0.53 vs 0.74±0.43; P=0.21; phase LF: 0.41±0.30 vs 0.43±0.26; P=0.64; vLF: 0.72±0.53 vs 0.66±0.16; P=0.18). In contrast, during the sit-to-stand protocol, coherence was lower following CR (pre vs post LF: 0.81±0.13 vs 0.79±0.16; p<0.01; vLF: 0.80±0.09 vs 0.79±0.14; p<0.01). In addition, gain was reduced post CR (pre vs post LF: 0.59±0.35 vs 0.55±0.31; P=0.02; vLF: 0.76±0.33 vs 0.61±0.37; p<0.01), suggesting CR-induced improvements in CA efficiency. However, phase remained unchanged pre- and post- CR during the sit-to-stand protocol (LF: 1.01±0.71 vs 0.84±0.58; P=0.17; vLF: 1.16±0.69 vs 1.08±0.60; P=0.19). Taken together, these findings demonstrate that a 12-week exercise-based CR program improves dynamic CA efficiency after a cardiac event. These novel results highlight the potential role of exercise training in improving cerebrovascular regulation. Funding: NIH AG073726 and Mayo Clinic This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Pediatric metabolic dysfunction–associated steatotic liver disease (MASLD) has become more prevalent on a global scale over the last decades and is associated with significant comorbidities in childhood and a 40-fold higher risk of early mortality in young adulthood. MASLD has now become the leading indication for liver transplantation in young adults in the United States. However, pediatric MASLD is still perceived as an indolent condition by many patients, families, and clinicians. In this Call to Action, we aim to raise awareness of pediatric MASLD as a public health crisis. Herein, we describe insufficient screening and disease staging practices, and a lack of accurate non-invasive tests and effective pharmacotherapy, both stemming from a paucity of multicenter clinical trials in pediatric MASLD. We provide clear steps to address this public health emergency by promoting awareness campaigns, educating and empowering patients and families, addressing barriers including access to care, nutritional and exercise support programs, establishing multidisciplinary care, launching community initiatives, and conducting clinical trials in pediatric MASLD for an age-based evaluation of novel diagnostic and therapeutic options. We conclude by highlighting the urgent need for comprehensive public health policies to control the tide of pediatric MASLD and call upon stakeholders to act now.

OBJECTIVE In many individuals, type 2 diabetes (T2D) remains poorly controlled despite taking multiple glucose-lowering therapies. Several studies have demonstrated that endogenous hypercortisolism is prevalent among these individuals. We tested whether cortisol-directed therapy improves their glycemic control. RESEARCH DESIGN AND METHODS In this prospective, multicenter, double-blind study, 136 individuals with T2D (hemoglobin A1c [HbA1c] 7.5%–11.5% [58–102 mmol/mol] on multiple medications) and hypercortisolism (by dexamethasone suppression test) were randomized 2:1 to the glucocorticoid receptor antagonist mifepristone (300–900 mg once daily; n = 91) or placebo (n = 45) for 24 weeks, with stratification by presence/absence of an adrenal imaging abnormality. The primary end point was the change in HbA1c. Secondary end points included changes in glucose-lowering medications, weight, and waist circumference and safety. RESULTS Mean baseline HbA1c in the study cohort was 8.55% (69.9 mmol/mol). At 24 weeks, the least squares mean (LSM) difference from placebo in HbA1c was −1.32% (95% CI −1.81 to −0.83; P &lt; 0.001). Participants receiving mifepristone experienced reductions in body weight and waist circumference (placebo-adjusted LSM differences of −5.12 kg [95% CI −8.20 to −2.03] and −5.1 cm [−8.23 to −1.99], respectively). Of participants on mifepristone, 46% discontinued therapy, compared with 18% on placebo. Adverse events with mifepristone (&gt;10% of participants) included hypokalemia, fatigue, nausea, vomiting, headache, peripheral edema, diarrhea, and dizziness, consistent with mifepristone’s known tolerability profile. Increases in blood pressure also occurred. CONCLUSIONS In individuals with inadequately controlled T2D and hypercortisolism, cortisol-directed medical therapy with mifepristone reduced HbA1c, with a manageable tolerability profile.

Introduction: Atherosclerotic arterial disease is the leading cause of death throughout the world. One of the most advanced forms of atherosclerosis, peripheral arterial disease (PAD), affects over 8.5 million people in the United States and over 230 million globally. This disease begins from an inflammatory lesion, known as the fatty streak, formed by mononuclear phagocytes (MNPs), a broad cell type classification that includes monocytes, dendritic cells, and macrophages. Development of more efficacious treatments for PAD requires that we better understand the cellular and molecular processes by which MNPs form these inflammatory lesions. Methods: To compare gene expression of MNPs, we performed scRNAseq on PBMCs from an initial cohort of 4 patients with PAD, mild claudicants to minor tissue loss (Rutherford 1-5), and 5 healthy individuals, defined as those without any chronic diseases and a hsCRP <2.0 mg/L. We conducted single cell RNA library generation using Parse Bio and sequenced to a depth of 70k reads per cell and downstream bioinformatic and differentially gene expression analysis via R and Seurat. Results: Gene expression differences in healthy versus PAD cells were visualized on a UMAP plot. Aligning our cells to the human PBMC Cell Atlas, we found that the cell type with the greatest transcriptional change (healthy vs. PAD) was CD14 + MNPs. Next, we screened for differentially expressed genes within this CD14 + MNP cluster between healthy and PAD subjects and identified 854 upregulated and 730 downregulated genes (log 2 fold change ≥ 0.25 and p < 0.05, Welch’s t-test). Two of the most significantly upregulated genes in PAD CD14 + MNPs are FAM20A and TMTC1. FAM20A encodes a psuedokinase important in calcium homeostasis as well as bone mineralization and that is upregulated in advanced atherosclerotic plaques. TMTC1 encodes for an endoplasmic reticulum protein also involved in calcium homeostasis, vascular homeostasis, and endothelial cadherin egress. Finally, one gene we found downregulated in PAD is CD83, a molecule implicated in resolution of inflammation, that when downregulated promotes an inflammatory state. Conclusion: Based on these findings we hypothesize that in PAD there exists a distinct transcriptional program along the CD14 + MNP cell type lineage that is pro-inflammatory and that may play a role in disease progression and response to intervention.

Introduction: Previous findings suggest that sirtuin 6 (SIRT6), a nuclear histone deacetylase, is involved in fundamental processes that regulate aging, which include DNA damage repair and maintenance of genomic stability. It remains unclear, however, whether SIRT6 overexpression can mitigate age-related vascular dysfunction due to multiple mechanisms of posttranslational enzyme inactivation (oxidation, ubiquitination-dependent degradation, etc). We hypothesized that overexpression of SIRT6, will improve both endothelium-dependent relaxation and smooth muscle contractile function and improve molecular mechanisms underlying these functions in healthy aged mice. Methods: We used normocholesterolemic mice that were either wild-type for SIRT6 (WT) or overexpressing one copy of SIRT6 (TG) and studied them at either 3 or 18 months of age. We assessed molecular changes in SIRT6 expression, cellular senescence, and vascular contractile protein expression using qPCR, and aortic rings in isolated organ bath chambers to measure endothelium-dependent relaxation to acetylcholine (ACH), endothelium-independent relaxation to sodium nitroprusside (SNP), and contractile responses to serotonin (5HT) and PGF 2α . Results: As expected, overexpression of SIRT6 in TG mice resulted in ~3-fold mRNA expression increase compared to WT mice in aorta. In line with our previous reports, SIRT6 mRNA levels significantly increased with age in aorta. CDKN2A, a cellular senescence marker, increased with aging in WT mice. Surprisingly, SIRT6 overexpression did not attenuate this increase, with TG mice tending to have higher CDKN2A expression than WT at 18m. ACTA2, a contractile protein marker, had modest reductions with age in WT mice, and surprisingly, overexpression of SIRT6 did not alter ACTA2 levels compared to WT at either time point. Finally, overexpression of SIRT6 did not mitigate age-related changes in vascular relaxation or contractile function. Conclusion: Collectively, these data at the surface level suggest that overexpressing SIRT6 does not protect against conduit vessel dysfunction in aged mice and is associated with paradoxical increases in senescent cell markers. It remains elusive whether there are other molecular modulators of aging that offset or alter the activity of SIRT6 with its genetic overexpression. Therefore, future studies investigating molecular determinants of SIRT6 bioactivity and its tissue/context dependence with aging are warranted.

Introduction: Atherosclerosis, the underlying cause of cardiovascular disease (CVD), is a lipid-driven chronic inflammatory disease. We have identified the co-stimulatory CD40-CD40L immune checkpoint dyad as a key driver of inflammation during atherosclerosis. CD40 and CD40L exert cell-type divergent functions via different signaling pathways. Hypothesis: We hypothesize that CD40 on endothelial cell (ECs) induces endothelial-to-mesenchymal transition (EndMT)-mediated vascular inflammation in atherosclerosis. Methods & Results: Using single cell RNAseq, we found that CD40 (TNFRSF5) is expressed on PDE3A + GJA5 + and KDR + COL15A1 + ECs of advanced human carotid atherosclerotic plaques. CD40 is highly expressed in the endothelial lining of human and mouse atherosclerotic plaques, and colocalizes with the EndMT markers fibronectin and collagen and adhesion molecule ICAM-1. CD40L activation of human aortic endothelial cells (HAECs) results in expression of the EndMT markers fibronectin, vimentin, sm22α, FSP1 and snail. Activation of CD40 in EC induces filamin A dependent translocation of CD40 into lipid rafts, increases TNF-receptor associated factor (TRAFs) -2, -3 and 6 levels, induces Akt signaling and increases expression of VCAM1 and CCL2. Conclusions: The endothelial cell has been more and more regarded as a cell type that plays a major role in driving inflammation. Our data suggest that the CD40-CD40L axis plays a significant role in EC-mediated inflammation in atherosclerosis by driving EndMT.

Goals: Our aim was to perform a national survey of provider attitudes, practices, and knowledge regarding weight loss and MASLD medications in patients with MASLD. Background: While weight loss is a cornerstone in the management of metabolic dysfunction-associated steatotic liver disease (MASLD), FDA-approved medications for weight loss remain underutilized. Results: We conducted a survey before resmetirom approval of hepatology and gastroenterology providers practicing in 44 states. Surveys were sent to 747 providers with 304 complete responses (41%), of whom 260 (86%) work at a liver transplant center. While nearly all respondents (96%) believed that weight loss medications could benefit patients with MASLD, 77% have never/rarely prescribed them due to low comfort (81%). Among weight loss medication prescribers, glucagon-like peptide-1 (GLP-1) receptor agonists were preferred (66%). In contrast, 63% had prescribed off-label medications for MASLD in the past 12 months, most commonly vitamin E (30%) and GLP-1 receptor agonists (25%). The top reported barriers to prescribing weight loss medications were lack of training/unfamiliarity, cost/insurance coverage, and side-effects, which may be explained by low formal obesity education and lack of knowledge (only 33% of FDA-approved medications for weight loss were correctly identified by >50% of providers). Overall, there was reasonable provider-reported adherence to the 2023 AASLD practice guidance for MASLD. Conclusions: This nationwide survey of hepatology and gastroenterology providers before resmetirom demonstrates that while off-label prescribing for MASLD was common, weight loss medication prescription rates remain very low due to low comfort possibly from insufficient education despite strong beliefs that they can benefit patients with MASLD.

The exact physiological role of BACE2 in endothelial function of systemic arteries is unknown. Our study shows that thromboxane A2 and prostaglandin F2α are responsible for impairment of endothelium-dependent relaxations in endothelium-specific BACE2-deficient mice. The data support an important role of BACE2 in the control of endothelial arachidonic acid metabolism and vasomotor function.