Biology subjects

Dahl, R.

Publications and source records attributed to Dahl, R..

5 recordsLinked to original sources

bioRxiv2026

Positive allosteric modulator of SERCA pump NDC-1171 attenuates cardiac functional decline in mouse model of Duchenne muscular dystrophy

Progressive cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD). Dysregulation of calcium handling has been implicated in cardiomyopathy progression in DMD. Here we describe a therapeutic approach to improve calcium homeostasis in a mouse model of DMD using the novel therapeutic NDC-1171, which is a positive allosteric modulator of the sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) pump. We synthesized NDC-1171 and treated 4-week-old D2.mdx mice (n=9) via oral gavage. A group of D2.mdx mice (n=9) and a group of DBA/2J mice (n=9; background strain) received a vehicle on the same schedule. We used ultrasound to assess left ventricular function, followed by a treadmill exhaustion test and a 4-paw grip strength test to assess skeletal muscle function. NDC-1171 attenuated cardiac functional decline in D2.mdx mice. At 16 weeks of age, left ventricular ejection fraction (LVEF) was significantly preserved in mice treated with NDC-1171 (57.7{square}{+/-}{square}0.5%) compared to mice treated with a vehicle (50.7{square}{+/-}{square}0.9%, p{square}<{square}0.05), though remained lower than background strain controls (62.4{square}{+/-}{square}0.6%). In contrast, functional behavior testing revealed no significant improvement in skeletal muscle function with treatment. These data suggest that treatment with the SERCA pump modulator NDC-1171 helps preserve cardiac function in a murine model of DMD, even as skeletal muscle function was impaired. Future work will be needed to determine if the benefits of this novel SERCA activator translate to large animal and clinical studies, but these initial results are promising and could help guide development of future treatments for pediatric patients with muscular dystrophy.

pharmacology and toxicology↗

bioRxiv2025

Insulin stimulated upregulation of OCTN2 carnitine transporters is impaired in patients with Primary carnitine deficiency

BackgroundPrimary carnitine deficiency (PCD) is an autosomal recessive disorder characterized by a lack of functional carnitine transporters OCTN2 (Organic Cation/Carnitine Transporter 2), which has been linked to several cases of sudden death in young Faroese individuals. It causes low carnitine levels and can present with hypoketotic hypoglycemia, skeletal and cardiac myopathy. Patients are treated with L-carnitine, and even while receiving treatment, skeletal muscle carnitine levels are only approximately 7% of normal. The regulation of the carnitine transporter, OCTN2, is not fully understood, but a combination of hypercarnitinaemia with hyperinsulinemia upregulates skeletal muscle carnitine uptake and OCTN2 mRNA expression. ObjectiveThe question arises as to whether hyperinsulinemia increases the efficiency of L-carnitine supplementation in PCD. The present study investigates the regulatory mechanisms behind insulin-induced carnitine uptake, and whether the combination of hypercarnitinaemia and hyperinsulinaemia increases skeletal muscle carnitine levels in patients with PCD. In addition to our main goals, we also explored the measurement of whole-body fat oxidation at rest and during exercise MethodNine patients with PCD (homozygous for the c.95 A > G, pN32S mutation) and nine healthy controls matched to age and body mass index (BMI) participated in the study. A six hour hyperinsulinemic clamp was supplemented with infusion of L-carnitine the last five hours. Skeletal muscle biopsies were collected before and after the clamp and carnitine content was measured. Furthermore, confocal microscopy was used to access regulation of OCTN2 and GLUT4 positive vesicles due to insulin stimulation and additionally whole body fat oxidation was measured with indirect calorimetry. ResultsWe found that the combination of hypercarnitinaemia with hyperinsulinemia did not increase skeletal muscle total carnitine levels significantly for neither patients with PCD [4.5 (SE 0.6) to 5.3 (SE 0.5) mmol {middle dot} kg-1] (P = 0.28) nor controls [19.8 (SE 0.6) to 21.2 (SE 0.5) mmol {middle dot} kg-1] (P = 0.053). The muscle carnitine profile showed that patients with PCD have low levels of total and free carnitine in skeletal muscle, but normal levels of acetylcarnitines corresponding to 60% of total carnitine (normal is [~]16% of total muscle carnitine). The results from confocal microscopy indicate that insulin regulates skeletal muscle carnitine uptake by stimulating OCTN2 recruitment from intracellular storages to the plasma membrane. This regulatory mechanism is however impaired in patients with PCD. Furthermore, we found that PCD patients were more dependent on carbohydrates at rest. In regard to fat oxidation, no difference was found between PCD and control group during short-term exercise. ConclusionsThe study indicates that insulin stimulates translocation of OCTN2 to the plasma membrane in healthy controls, a mechanism that seems to be impaired in patients with PCD. The combination of hypercarnitinaemia with hyperinsulinemia did not increase skeletal muscle total carnitine levels significantly (P = 0.28) in patients with PCD.

molecular biology↗

bioRxiv2025

Failed Metabolic Adaptation to Stress Underlies Pathogenesis in a Heterozygous Genetic Disorder

Disorders linked to heterozygous variants occupy a continuum in terms of the timing and severity of phenotypic emergence. An important question regarding this variability entails the effect stress has on the residual protein function. Using Darier disease (DD), caused by heterozygous variants of the SERCA2 calcium pump, as a model, we uncovered a potential connection between extrinsic stress and pathogenesis. The skin lesions characteristic of DD entail loss of intercellular adhesion and rarely appear pre-adolescence, suggesting that factors beyond heterozygosity contribute to disease pathogenesis. Testing whether age-related stressors contribute to DD, we show that DD patient-derived keratinocytes subjected to stress yield twice the reactive oxygen species of controls, accompanied by greater disruption of intercellular adhesion. Metabolic analysis of DD cells revealed perturbation of the pentose phosphate pathway (PPP), a stress response system responsible for regenerating antioxidants like glutathione. At baseline, DD cells had less free glutathione but an increase in protective glutathione-based modifications of SERCA2, a reversible form of protein oxidation. With stress, DD cells form an aberrant, heavily glutathionylated perinuclear halo consisting of keratin and the intercellular adhesion component, desmoplakin. We propose a model whereby SERCA2 heterozygosity causes mild oxidative stress that under homeostatic conditions can be buffered by glutathionylation. When stressed, the depleted glutathione store is shunted towards the desmoplakin-intermediate filament system at the expense of SERCA2, rendering it vulnerable to damage. A lesional flare, then, would represent a case of more complete SERCA2 inhibition and a novel example of how heterozygous disorders interact with stress to disrupt intercellular adhesion.

cell biology↗

bioRxiv2020

Brucella suppress innate immunity by down-regulating STING expression in macrophages

Brucellosis, caused by Brucella bacteria species, remains the most prevalent zoonotic disease worldwide. Brucella establish chronic infections within host macrophages despite triggering cytosolic innate immune sensors, including Stimulator of Interferon Genes (STING), which potentially limit infection. In this study, STING was required for control of chronic Brucella infection in vivo. However, early during infection, Brucella down-regulated STING mRNA and protein. Down-regulation occurred post-transcriptionally, required live bacteria, the Brucella type IV secretion system, and was independent of host IRE1-RNase activity. Rather, Brucella induced a STING-targeting microRNA, miR-24-2. Furthermore, STING downregulation was inhibited by miR-24 anti-miRs and in mirn23a locus-deficient macrophages. Failure to suppress STING expression in mirn23a-/- macrophages correlated with diminished Brucella replication, and was rescued by exogenous miR-24. Anti-miR-24 potently suppressed replication in wild type, but much less in STING-/- macrophages, suggesting most of the impact of miR-24 induction on replication occurred via STING suppression. In summary, Brucella sabotages innate immunity by miR-24-dependent suppression of STING expression; post-STING activation "damage control" via targeted STING destruction may enable establishment of chronic infection. Author summaryCytosolic pattern recognition receptors, such as the nucleotide-activated STING molecule, play a critical role in the innate immune system by detecting the presence of intracellular invaders. Brucella bacterial species establish chronic infections in macrophages despite initially activating STING. STING does participate in the control of Brucella infection, as mice or cells lacking STING show a higher burden of Brucella infection. However, we have found that early following infection, Brucella upregulates a microRNA, miR-24, that targets the STING messenger RNA, resulting in lower STING levels. Dead bacteria or bacteria lacking a functional type IV secretion system were defective at upregulating miR-24 and STING suppression, suggesting an active bacteria-driven process. Failure to upregulate miR-24 and suppress STING greatly compromised the capacity for Brucella to replicate inside macrophages. Thus, although Brucella initially activate STING during infection, the ensuing STING downregulation serves as a "damage control" mechanism, enabling intracellular infection. Viruses have long been known to target immune sensors such as STING. Our results indicate that intracellular bacterial pathogens also directly target innate immune receptors to enhance their infectious success.

microbiology↗

bioRxiv2019

Distentangling the systems contributing to changes in learning during adolescence

Multiple neurocognitive systems contribute simultaneously to learning. For example, dopamine and basal ganglia (BG) systems are thought to support reinforcement learning (RL) by incrementally updating the value of choices, while the prefrontal cortex (PFC) contributes different computations, such as actively maintaining precise information in working memory (WM). It is commonly thought that WM and PFC show more protracted development than RL and BG systems, yet their contributions are rarely assessed in tandem. Here, we used a simple learning task to test how RL and WM contribute to changes in learning across adolescence. We tested 187 subjects ages 8 to 17 and 53 adults (25-30). Participants learned stimulus-action associations from feedback; the learning load was varied to be within or exceed WM capacity. Participants age 8-12 learned slower than participants age 13-17, and were more sensitive to load. We used computational modeling to estimate subjects use of WM and RL processes. Surprisingly, we found more robust changes in RL than WM during development. RL learning rate increased significantly with age across adolescence and WM parameters showed more subtle changes, many of them early in adolescence. These results underscore the importance of changes in RL processes for the developmental science of learning.\n\nHighlights- Subjects combine reinforcement learning (RL) and working memory (WM) to learn\n- Computational modeling shows RL learning rates grew with age during adolescence\n- When load was beyond WM capacity, weaker RL compensated less in younger adolescents\n- WM parameters showed subtler and more puberty-related changes\n- WM reliance, maintenance, and capacity had separable developmental trajectories\n- Underscores importance of RL processes in developmental changes in learning

neuroscience↗