Background/Objectives: Peroxisome proliferator-activated receptor gamma (PPARγ) is a fatty acid-binding transcription activator of the adipokine chemerin. The key role of PPARγ in adipogenesis was established by reports on adipose tissue-resident macrophages that express PPARγ. The present study examined PPARγ⁺ macrophages in human skeletal muscle tissues, their response to fatty acid (FA) species, and their correlations with age, obesity, adipokine expression, and an abundance of other macrophage phenotypes. Methods: An ex vivo human skeletal muscle model with surgical specimens that were maintained without or with FAs for up to 11 days was utilized. Immunofluorescence analysis was used to detect macrophage phenotypes and mitochondrial activity. Preconfigured arrays were used to detect the expression of 34 different adipokines and chemokines. Results: Data from 14 adults revealed that PPARγ⁺ macrophages exclusively reside in intermuscular adipose tissue (IMAT), and their abundance correlates with the metabolic status of surrounding adipocytes during tissue maintenance in vitro for 9–11 days. Elevated fatty acid levels lead to significant increases in PPARγ⁺ populations, which are correlated with the donor’s body mass index (BMI). Conclusions: PPARγ⁺ macrophages represent a distinctly specialized population of regulatory cells that reside within human IMATs in accordance with their metabolic status. Thus, future in-depth studies on IMAT-resident PPARγ⁺ macrophage action mechanisms will elucidate the role of skeletal muscle in the pathogenesis of human metabolic dysfunction.

Neuromuscular junctions (NMJs) connect motor neurons to muscle fibers, enabling electrical-to-chemical signal transmission and sensing of mechanical forces. We employed a previously introduced human skeletal muscle tissue model to study the NMJ presynaptic terminal (PT). Using immunohistochemical approaches, we analyzed PT formation in samples from 12 participants, either immediately after surgery or following 11 days of in vitro maintenance. In immediate postsurgical samples, the number, size, and integrated immunofluorescence intensity of detectable PTs increased with participant age, accompanied by elevated expression of neurotrophic and inflammatory proteins. Moreover, CD80⁺ and CD206⁺ macrophages were detected near PTs, suggesting a potential regulatory role in PT formation. Prolonged in vitro maintenance of muscle samples in a quiescent state for 11 days reproduced age-associated PT features and further increased PT spatial expansion and fragmentation. Notably, increased PT fragmentation positively correlated with participant body mass index (BMI), suggesting a possible link between metabolic status and PT remodeling. Consistently, the activation of skeletal muscle metabolism through long-chain fatty acid supplementation partially restored PT formation in vitro. Together, these findings highlight the utility of human skeletal muscle tissue models for investigating NMJ dynamics in pathological contexts and for identifying therapeutic strategies aimed at delaying or preventing neuromuscular decline.

Background/Objectives: Presynaptic terminals (PTs) in the neuromuscular junction (NMJ) are essential regulators of skeletal muscle function and are responsible for the translation of electrical impulses from motor neurons into muscle contraction. The present exploratory study aimed to compare PT adaptations in spinalis muscle samples from the concave and convex regions of the spine in three cases of advanced scoliosis, which exhibited marked asymmetry in muscle development. Methods: Spinalis muscle sample pairs were retrieved after surgical procedures and subjected to immunofluorescence (IF)-based spatial analysis of PTs, histological assessment of muscle fibers, and expression analyses of inflammatory and neurotrophic proteins. Results: IF images revealed distinct differences in PT parameters between spinalis samples obtained from the corresponding concave and convex sides of spinal deformities. Advanced statistical models revealed a consistent tendency for concave spinalis muscles to develop lower PT numbers, along with decreased expression of relevant components, neurofilament M, and synaptic vesicle glycoprotein 2. Moreover, these impairments were accompanied by increased expression levels of IFN alpha, which has been previously implicated in NMJ disorders, neuropathies, and myopathies. Conclusions: In the concave regions of spinal deformities, continuously compressed spinalis muscles may be particularly susceptible to PT alteration and denervation. However, comprehensive multicenter validation studies are required to better define the relationships among PT alterations, IFN alpha expression, and muscle tissue compression.