Sieck, Gary

In human airway smooth muscle cells, TNFα induces reactive oxygen species (ROS) generation and promotes endoplasmic reticulum (ER) stress and mitochondrial fragmentation. Importantly, treatment with the ROS scavenger tempol effectively attenuated TNFα-induced oxidative stress, suppressed ER stress and mitochondrial fragmentation, and improved the intrinsic respiratory capacity and functional efficiency of individual mitochondria. These findings identify oxidative stress as a central mediator linking TNFα signaling to ER stress and mitochondrial fragmentation, highlighting tempol as a potential therapeutic strategy.

This study found that inhibiting TrkB kinase activity decreases the extent of neuromuscular transmission failure during repetitive stimulation at low frequency while increasing failure with high-frequency stimulation. The frequency-dependent effect of 1NMPP1 treatment suggests that the role of TrkB signaling in maintaining neuromuscular transmission during repetitive stimulation may differ between motor unit types (slow-twitch, fatigue-resistant vs. fast-twitch, fatigable) and likely reflect effects at the presynaptic terminal without major effects on the muscle itself.

The study establishes the presence of a robust mitophagic response to acute mitochondrial depolarization in hASM cells mediated through the canonical PINK1-Parkin pathway. By integrating quantitative mitochondrial labeling and biochemical analyses, we demonstrate increased mitochondrial damage and remodeling, accompanied by mitochondrial PINK1 accumulation and Parkin activation, resulting in ubiquitin-dependent signaling and lysosomal engulfment. These findings identify mitophagy as a critical adaptive mechanism for maintaining mitochondrial quality control in airway smooth muscle cells during metabolic stress.

Aging selectively impacts the function of type IIx/IIb fibers in the diaphragm muscle. We show that sarcopenia reduces maximum specific force, maximum shortening velocity, and peak power output, whereas endurance during repetitive contractions is preserved. These findings explain why higher force airway clearance behaviors decline with age, whereas fatigue-resistant breathing behavior remains resilient.

Neuroplastic changes in phrenic motor neurons that underlie recovery from spinal cord injury may be mediated by perineuronal nets. We show that changes in perineuronal nets around phrenic motor neurons occur within 7 days after cervical spinal cord injury, and that the increase in perineuronal nets around larger phrenic motor neurons was more pronounced. These changes are consistent with substantial reorganization of the neural network onto intact phrenic motor neurons following cervical spinal cord injury.

The present study provides novel physiological insights into aging by measuring airway compliance and residual volume via forced oscillation perturbations using a programmable mechanical ventilator (flexiVent—currently considered a gold standard for in vivo lung function measurements). In addition, dynamic measurements of lung inflation reported herein may serve as early indicators of altered elastic properties. Taken together, the findings offer a comprehensive assessment of age-related changes in lung structure and function.

We introduce an imaging-based approach to quantitatively distinguish intact from damaged mitochondria within heterogeneous mitochondrial networks using fluorescent labels that exhibit different sensitivities to mitochondrial membrane potential. By combining membrane potential-independent CellLight GFP label with membrane potential-dependent MitoTracker Red, this method sensitively quantifies basal and stress-induced mitochondrial damage in hASM cells. This assay provides a practical and interpretable metric of mitochondrial integrity that complements existing methods that measure mitochondrial membrane potential and oxidative stress.

ABSTRACT Motor neuron plasticity and survival depend on several trophic factors, with signaling via the tropomyosin receptor kinase B (TrkB) receptor being particularly important beyond development and across the lifespan. We hypothesized that differences in motor neuron properties may reflect differential trophic influences across motor units within a single motor unit pool. Based on extensive previous characterization of rat phrenic motor neurons (PhMN), somal surface area was used as an indicator of motor unit type (smaller neurons innervating slow‐twitch, fatigue‐resistant units versus larger neurons innervating fast‐twitch, fatigable units). To examine whether TrkB expression reflects these size‐related properties, TrkB mRNA transcripts were studied in individual PhMNs labeled retrogradely with Alexa Fluor 488‐conjugated cholera toxin subunit β from five adult male Sprague–Dawley rats. Longitudinal sections of the cervical C3–C5 spinal cord (10 μm thick) were processed using fluorescence in situ hybridization (RNAscope) and imaged using confocal microscopy to measure individual PhMN size and full‐length TrkB mRNA transcripts in nuclear and cytoplasmic compartments. Across 287 PhMNs, significant size variation existed both within and between animals. Across all animals, somal surface area averaged 4385 ± 1627 μm 2 with mean values per animal ranging from 3544 to 5461 μm 2 . PhMNs were classified into tertiles within each animal based on somal surface area. Individual PhMNs averaged 1070 ± 685 TrkB mRNA transcripts per motor neuron. Larger PhMNs in the upper tertile by size expressed a greater total number of TrkB mRNA transcripts per motor neuron, with values on average threefold higher compared to smaller motor neurons in the lower tertile ( p < 0.001). Cytoplasmic and nuclear TrkB mRNA density (transcripts/volume) displayed no significant effect of PhMN somal surface area tertile. Overall, the greater TrkB mRNA levels in larger motor units responsible for higher force, expulsive motor behaviors may underlie their functional adaptations and resilience to injury or disease. image

Airway hyperreactivity and hASM cell proliferation (hyperplasia) are hallmark characteristics of asthma. The results of the present study showed that short-term exposure of nonasthmatic hASM to TNFα (a proinflammatory cytokine) can also induce hASM cell proliferation via activation of an ER stress pathway. Identification of the ER stress signaling pathway as important in mediating hASM hyperplasia may provide an important therapeutic target for treating asthma or acute inflammation.