Citations

Phrenic motor neurons (PhMNs) innervate the diaphragm muscle (DIAm), the primary pump muscle involved in breathing. It has been shown that brain-derived neurotrophic factor (BDNF) signals through its high-affinity, full-length tropomyosin receptor kinase B (TrkB.FL) to promote PhMN survival in embryonic and early postnatal development. Reduced BDNF/TrkB.FL signaling also appears to be involved in the age-related loss of PhMNs. Previously, we developed a novel chemogenetic rat model ( TrkB F616 rat) in which insertion of a knock-in allele sensitive to 1NMPP1 (a selective kinase inhibitor) allows rapid inhibition of TrkB.FL kinase activity. Using this TrkB F616 rat, we found that in younger animals, a 14-day period of 1NMPP1-induced TrkB.FL kinase inhibition resulted in an ~20% loss of larger PhMNs similar to that found with aging. Previous studies from our laboratory demonstrated that BDNF/TrkB.FL signaling induces pCREB S133 phosphorylation at serine residue 133 in PhMNs. 1NMPP1 induced inhibition of TrkB.FL kinase activity in TrkB F616 rats acutely blunts pCREB S133 phosphorylation induced by intrathecal BDNF treatment. In another cell type, we showed that pCREB S133 transcriptionally targets PGC1α expression with downstream upregulation of expression of mitochondrial transcription factor A (TFAM) and mitochondrial biogenesis. Based on a bioinformatic analysis, we identified a putative binding site for pCREB S133 in the rat PGC1α promoter. In the present study, we hypothesized that BDNF/TrkB.FL signaling mediates pCREB S133 phosphorylation and downstream activation of PGC1α thereby promoting mitochondrial biogenesis. Adult female and male TrkB F616 rats (~ 3 months of age; 300 g) were anesthetized (ketamine/xylazine) and either 25 μM 1NMPP1 or DMSO (vehicle control) was injected ip. After 2 h, the rats were treated intrathecally (infused at C 4 ) with 100 ng/ml BDNF for 40 min. Thereafter, the animals were euthanized and the ventral cervical spinal cord containing PhMNs was dissected, and lysates were prepared for subsequent analyses. Western blot was performed to quantify pCREB S133 phosphorylation, and PGC1α mRNA and protein expression were measured by qPCR and Western blot, respectively. A chromatin immunoprecipitation (ChIP) assay confirmed that pCREB S133 binds to the PGC1α promoter and that compared to vehicle treated controls, 1NMPP1induced TrkB.FL kinase inhibition reduced the binding affinity of pCREB S133 . Consistent with these results, we found that pCREB S133 phosphorylation and PGC1α mRNA and protein expression were reduced following 1NMPP1-induced TrkB.FL kinase inhibition. We conclude that in the rat cervical ventral horn, BDNF/TrkB.FL signaling induces pCREB S133 phosphorylation which transcriptionally activates PGC1α expression and downstream mitochondrial biogenesis. The BDNF/TrkB.FL signaling pathway acting in concert with activity dependent signaling may converge on pCREB S133 phosphorylation to maintain the survival of PhMNs by promoting mitochondrial biogenesis. The loss of the contribution of BDNF/TrkB.FL signaling in old age and with neurodegeneration may lead to PhMN death. Supported by NIH grants AG44615 and HL146114 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.

In the elderly, age-associated muscle weakness and atrophy (sarcopenia) is prevalent in both limb and respiratory muscles. In the tongue muscles, dyscoordination and sarcopenia predisposes elderly individuals to dysphagia, dysphonia and a greater risk for aspiration pneumonias and obstructive sleep apnea. In humans and in the Fischer 344 rat model of aging, motor neuron (MN) death occurs in old age, and the selective vulnerability of fast-fatigable motor units to loss is consistent with behavioral deficits in airway defense (e.g., cough). However, whether the timing of MN loss is gradual across the lifespan or precipitous from late-middle-age is unknown. Recently, the concept of an age -related increase of systemic inflammatory cytokines has been implicated in the development of sarcopenia, although the mechanisms by which this occurs remain obscure. In other cell types, inflammation triggers an unfolded protein response and mitochondrial fragmentation – processes implicated in neuronal death and neurodegeneration. In this study of female and male Fischer 344 rats at 6-, 18- and 24-months-old, we evaluated serum inflammatory cytokines (TNFα, IL1β & IL6) via ELISA, medullary unfolded protein response (pIRE1a S724 & CDK5) and mitochondrial fragmentation (pDRP1 S616 ) via Western blot, hypoglossal MN mitochondrial volume density and mitochondrial fragmentation via serial blockface electron microscopy (SBFEM), hypoglossal MN survival via Nissl histology and stereological counting and tongue muscle (longitudinal and genioglossus) sarcopenia via uniaxial specific force assessment and cross-sectional muscle fiber areas. All data were analyzed by 1-way ANOVAs or Kruskal-Wallis nonparametric tests, depending on data distributions. Here, we show that a systemic inflammation-induced unfolded protein response in the medulla and hypoglossal MNs mitochondrial fragmentation is present at 18-months-old. This mitochondrial fragmentation is consistent with increased medullary expression of pDRP1 S616 . At this age, we did not observe any evidence of tongue muscle weakness or atrophy, nor any evidence of hypoglossal MN death. At 24-months old, hypoglossal MN mitochondrial deficits remained readily observable using SBFEM, with hypoglossal MN death (specific to larger MNs) and tongue muscle sarcopenia (selective to fast-fatigable type IIx fibers) present at this age. Overall, we conclude that denervation-related sarcopenia is precipitous from late-middle-age to old age in Fischer 344 rats. This MN death is triggered (or at least preceded), by an unfolded protein response and mitochondrial fragmentation. Interventions ameliorating inflammation, the unfolded protein response and/or mitochondrial breakdown may preserve MNs and prevent or reduce age-associated sarcopenia. This work was supported by NIH grants: HL166204 (MJF), AG086136 (MJF), HL157984 (GCS) & AG44615 (GCS) 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.

Age-associated muscle weakness and atrophy (sarcopenia) is prevalent in both limb and respiratory muscles. In the tongue muscles, dyscoordination and sarcopenia predisposes elderly individuals to dysphagia, dysphonia and a greater risk for aspiration pneumonias and obstructive sleep apnea. In humans and in the Fischer 344 rat model of aging, motor neuron (MN) death occurs in old age, and the selective vulnerability of fast-fatigable motor units to loss is consistent with behavioral deficits in airway defense (e.g., cough). However, in many aerodigestive behaviors, deficits in neuromotor coordination and the timing of motor unit activations may be more pertinent than frank weakness. In motor neurons, the substrate for the integration of sensory, pattern, executive and reflex activations is the dendritic arbour. Currently, it is unknown whether MN dendritic and dendritic spine degenerations occur in aging and if any changes are specific to the vulnerable larger MNs. In this study of female and male Fischer 344 rats at 6- and 24-months-old, we evaluated hypoglossal MN dendritic arbours and dendritic spines using golgi-cox impregnation and confocal imaging approaches in thick brainstem vibratome ex vivo slices (200 µm). All data were analyzed by unpaired t-tests, 2-way ANOVAs or Pearson’s correlations, where relevant. In 24-month-old rats, hypoglossal MN dendritic arbour length and surface area were reduced compared to 6-month controls. In 6-month-olds, dendritic length and surface area was dependent on somal size, with bigger MN somas having longer and larger dendritic arbours, a relationship lost in 24-month old hypoglossal MNs. Dendritic spine density was reduced in 24- compared to 6-month-old rats. Overall, our findings suggest that hypoglossal MN dendritic degenerations with aging are selective to MNs of fast-fatigable motor units. Interventions ameliorating neuromotor circuit and dendritic breakdown may preserve neuromotor function in old age. This work was supported by NIH grants: HL166204 & AG086136 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.

Neuromotor control of diaphragm muscle (DIAm) involves size-dependent recruitment of phrenic motor neurons (PhMNs). To accomplish breathing, only slow (type S) and fast, fatigue resistant (type FR) DIAm motor units are recruited. Thus, type s and FR DIAm motor units are very active in sustaining ventilation throughout life. Importantly, type S and FR DIAm motor units comprise small PhMNs that innervate type I and IIa DIAm fibers, respectively. More fatigable fast (type FF) motor units are very infrequently recruited for higher force, expulsive behaviors. Type FF DIAm motor units comprise large PhMNs that innervate type IIx/IIb DIAm fibers. Previously, we reported that compared to large PhMNs, small PhMNs have higher mitochondrial volume densities reflecting their more frequent activation. Using a quantitative histochemical technique to measure the maximum velocity of the succinate dehydrogenase reaction (SDH max ), we showed that type I and IIa DIAm fibers have higher oxidative capacity compared to type IIx/IIb fibers, which correlates with mitochondrial volume density and the more frequent activation of these muscle fibers. Accordingly, we hypothesize that the SDH max of small PhMNs is greater compared to large PhMNs. PhMNs in 6 month old, female and male Sprague Dawley rats were retrogradely identified by intrapleural injection of Alexa 647-conjugated cholera toxin B (CTB). Following retrograde CTB labeling, rats were perfused intracardially with a 0.1 M PBS, euthanized, and the C1–C6 segment of the spinal cord was dissected. Spinal cord sections were cut (40 mm) in longitudinal horizontal sections and mounted in 2-well Ibidi μ-slide plates. To measure SDH max , the sections were exposed to a solution containing 80 mM succinate (maximum substrate concentration) and 1.5 mM nitro blue tetrazolium (NBT; reaction indicator). As the SDH reaction proceeded, CTB-labeled PhMNs were imaged in 3D (Z optical slice of 0.5 μm) using an oil-immersion x60/1.4 NA objective on a Nikon Eclipse A1 laser scanning confocal system. The change in optical density (OD) was measured every 15 s over a 10-min period to measure the rate of accumulation of NBT diformazan (NBT dfz ; peak absorbance of 570 nm) in PhMNs. Using the Beer-Lambert equation, the change in OD was used to determine SDH max expressed as mmol fumarate/L cell/min. In separate experiments, following retrograde CTB labeling, mitochondria in PhMNs were labeled by transdural infusion of MitoTracker Red and imaged in 3D to determine mitochondrial volume density. Our results support a size-dependent heterogeneity in PhMN mitochondrial volume density and SDH max . We conclude that more active small PhMNs have a higher mitochondrial volume density and corresponding SDH max compared to large PhMNs. NIH grant AG44615 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.

Abstract Purpose: Navtemadlin is a potent small-molecule inhibitor of MDM2, which has completed a phase 0 window-of-opportunity study in glioblastoma (GBM). To optimally interpret the clinical data, a detailed analysis of navtemadlin pharmacokinetics (PK), pharmacodynamics, and efficacy was performed in GBM patient-derived xenografts (PDX). Experimental Design: Response to navtemadlin was characterized in vitro and in vivo in GBM PDXs with and without MDM2 amplification. Efficacy in vivo was integrated with measured plasma and intra-tumoral drug levels to develop a translational PK/efficacy model comparing exposure effective in PDX to exposure achieved in phase 0 patient samples. Results: In vitro, navtemadlin showed robust on-target activity in TP53–wild-type GBM. In vivo efficacy strongly correlated with MDM2 amplification status. In subcutaneous PDXs, navtemadlin significantly extended survival when dosed at 25 mg/kg in an MDM2-amplified PDX compared with 100 mg/kg in a non-amplified PDX. Central nervous system distribution was limited by blood–brain barrier efflux (Kp_brain = 0.009). In an MDM2-amplified orthotopic PDX model, navtemadlin was ineffective at 100 mg/kg; when established in mice with deficient blood–brain barrier efflux (Rag−/−Abcb1a−/−Abcg2−/−), 25 mg/kg doubled survival. A tumor PK/efficacy model was built to define target exposure for efficacy in GBM, using the effective 25 mg/kg dose. Modeled exposures exceeded this threshold in three (of 16) tumor samples from phase 0 study patients at the 240 mg dose level. Conclusions: Navtemadlin efficacy was highly dependent on adequate brain penetration. Our translational PK/efficacy model suggests that the minimum effective tumor exposures were achieved only in a minority of patients with GBM.

Aims The use of jumbo femoral heads, defined as those with a diameter of ≥ 40 mm, in primary total hip arthroplasty (THA) has gained popularity, to mitigate dislocation. The aim of this study was to determine the risk of dislocation, implant survival, and clinical outcomes of a large cohort of primary THAs with jumbo femoral heads. Methods We conducted a retrospective analysis of 1,828 primary THAs with jumbo femoral heads, which were undertaken for osteoarthritis, in 1,578 patients between January 2000 and December 2022, at a single academic medical centre. The femoral head diameter was 40 mm in 1,584 THAs (87%) and 44 mm in 244 THAs (13%). The outer diameter of the acetabular component ranged from 52 mm to 72 mm in those with 40 mm heads, and from 54 mm to 78 mm in those with 44 mm heads. The types of bearing included ceramic-on-highly cross-linked polyethylene (1,229 THAs; 67%) and metal-on-polyethylene (599 THAs; 33%). Elevated liners were used in 472 THAs (26%) and 1,083 (59%) were lateralized. The most common operative approach was posterior (1,388 THAs; 76%). Outcomes of interest included the rate of dislocation, revision for dislocation, any revision, any reoperation, and the Harris Hip Score (HHS). The mean age of the patients at the time of THA was 64 years (8 to 94); 1,477 (81%) were male, and their mean BMI was 28 kg/m² (5 to 55). The mean follow-up was six years (2 to 14). Results The ten-year survival free of dislocation was 97% (95% CI 96 to 98; 97% for 40 mm heads (95% CI 95 to 98) and 99% for 44 mm heads (95% CI 97 to 100) (hazard ratio 3 (95% CI 1 to 14); p = 0.106)). The ten-year survival free of revision for dislocation was 99.6% (95% CI 99 to 100) (99.5% for 40 mm heads (95% CI 98 to 100) and 100% for 44 mm heads (p = 0.546)). The ten-year survival free of any revision and any reoperation was 95% (95% CI 94 to 97) and 93% (95% CI 91 to 95), respectively. There were no significant differences in survival free of any revision (p = 0.746) or any reoperation (p = 0.762) between the two groups. Conclusion In this large single-centre study of the use of jumbo femoral heads in primary THAs, the ten-year survival free of dislocation was 97%, with extremely few revisions for dislocation. These results highlight the potential for jumbo femoral heads to reduce the risk of dislocation and enhance implant longevity without compromising other clinical outcomes. Cite this article: Bone Joint J 2025;107-B(7):698–706.

AbstractWe investigated how obesity impacts the response of circulating insulin‐like growth factor‐1 (IGF‐1) to a single bout of endurance exercise in humans with and without obesity. Blood samples were collected before exercise, at 15 and 40 min during a 45‐min cycling session at 65% of heart rate reserve, and 15 min post‐exercise. Serum levels of total IGF‐1, free IGF‐1, IGF binding proteins 1 (IGFBP‐1) and 3 (IGFBP‐3), growth hormone, and insulin were measured. Both total IGF‐1 and IGFBP‐3 serum concentrations increased significantly (p < 0.05) during exercise in the study participants without obesity but not in those with obesity, returning to basal levels immediately after exercise. There was a statistically significant main effect on the growth hormone response, with circulating levels being higher in participants without obesity (p < 0.05). No significant effects were observed for either free IGF‐1 or IGFBP‐1 serum concentrations in response to exercise in either group (p > 0.05). We conclude that humans with obesity have blunted serum total IGF‐1 response during exercise. However, a concurrent attenuation in serum IGFBP‐3 response, which regulates free (i.e., biologically active) IGF‐1 in circulation, results in no change in circulating free IGF‐1 levels during endurance exercise in individuals with obesity.

ABSTRACT Purpose The natural history of biochemical recurrence (BCR) after radical prostatectomy (RP) remains understudied, with limited long‐term data from large cohorts inclusive of both salvage radiotherapy (SRT)‐treated and untreated patients. Herein, we sought to evaluate the outcomes of patients with BCR and the impact of SRT on disease progression. Materials and Methods Patients undergoing RP who developed BCR (PSA ≥ 0.20 ng/mL) were included. Patients with BCR treated with SRT were compared to untreated patients using risk‐set matching with time‐dependent propensity scores. The primary outcome was metastases, analyzed using Kaplan–Meier and Cox models. The number needed to treat (NNT) with SRT to prevent progression was derived at 5 and 15 years. Results Among 6881 patients with BCR, 2109 received SRT. At a median follow‐up of 10.2 years, 1147 patients developed metastases. The median PSA at the time of SRT was 0.50 ng/mL. After 1:1 propensity score matching (2109 patients per cohort), SRT significantly reduced the risk of metastases at 5 (12.7% vs. 19.3%, p < 0.0001) and 15 years (28.6% vs. 31.5%, p < 0.001). On multivariable analysis, SRT independently reduced metastasis risk (HR 0.75, 95% CI 0.63–0.90, p = 0.002), translating to NNT of 23 and 15 at 5 and 15 years, respectively. Interaction analyses between SRT and nodal status ( p = 0.04) showed greater metastasis risk reduction in pN+ (HR 0.41, 95% CI 0.22–0.77, p = 0.005) compared to pN− disease (HR 0.81, 95% CI 0.67–0.97, p = 0.02). Conclusions Most patients with BCR post‐RP do not progress to metastasis. For those who do progress, SRT inarguably improves the oncologic outcomes in the BCR setting. However, careful patient selection and shared decision making should be encouraged in order to limit overtreatment and side effects.

The translation of AI-generated brain metastases (BM) segmentation into clinical practice relies heavily on diverse, high-quality annotated medical imaging datasets. The BraTS-METS 2023 challenge has gained momentum for testing and benchmarking algorithms using rigorously annotated internationally compiled real-world datasets. This study presents the results of the segmentation challenge and characterizes the challenging cases that impacted the performance of the winning algorithms. Untreated brain metastases on standard anatomic MRI sequences (T1, T2, FLAIR, T1PG) from eight contributed international datasets were annotated in stepwise method: published UNET algorithms, student, neuroradiologist, final approver neuroradiologist. Segmentations were ranked based on lesion-wise Dice and Hausdorff distance (HD95) scores. False positives (FP) and false negatives (FN) were rigorously penalized, receiving a score of 0 for Dice and a fixed penalty of 374 for HD95. The mean scores for the teams were calculated. Eight datasets comprising 1303 studies were annotated, with 402 studies (3076 lesions) released on Synapse as publicly available datasets to challenge competitors. Additionally, 31 studies (139 lesions) were held out for validation, and 59 studies (218 lesions) were used for testing. Segmentation accuracy was measured as rank across subjects, with the winning team achieving a LesionWise mean score of 7.9. The Dice score for the winning team was 0.65 ± 0.25. Common errors among the leading teams included false negatives for small lesions and misregistration of masks in space. The Dice scores and lesion detection rates of all algorithms diminished with decreasing tumor size, particularly for tumors smaller than 100 mm3. In conclusion, algorithms for BM segmentation require further refinement to balance high sensitivity in lesion detection with the minimization of false positives and negatives. The BraTS-METS 2023 challenge successfully curated well- annotated, diverse datasets and identified common errors, facilitating the translation of BM segmentation across varied environments and providing the tools for future development of personalized volumetric reports to patients undergoing BM treatment.