We investigated the shuttling of Homer protein isoforms identified in soluble (cytosolic) vs. insoluble (membrane–cytoskeletal) fraction and Homer protein–protein interaction/activation in the deep postural calf soleus (SOL) and non-postural gastrocnemius (GAS) muscles of het−/− mice, i.e., mice with an autosomal recessive variant responsible for a vestibular disorder, in order to further elucidate a) the underlying mechanisms of disrupted vestibular system-derived modulation on skeletal muscle, and b) molecular signaling at respective neuromuscular synapses. Heterozygote mice muscles served as the control (CTR). An increase in Homer cross-linking capacity was present in the SOL muscle of het−/− mice as a compensatory mechanism for the altered vestibule system function. Indeed, in both fractions, different Homer immunoreactive bands were detectable, as were Homer monomers (~43–48 kDa), Homer dimers (~100 kDa), and several other Homer multimer bands (>150 kDA). The het−/− GAS particulate fraction showed no Homer dimers vs. SOL. The het−/− SOL soluble fraction showed a twofold increase (+117%, p ≤ 0.0004) in Homer dimers and multimers. Homer monomers were completely absent from the SOL independent of the animals studied, suggesting muscle-specific changes in Homer monomer vs. dimer expression in the postural SOL vs. the non-postural GAS muscles. A morphological assessment showed an increase (+14%, p ≤ 0.0001) in slow/type-I myofiber cross-sectional area in the SOL of het−/− vs. CTR mice. Homer subcellular immuno-localization at the neuromuscular junction (NMJ) showed an altered expression in the SOL of het−/−mice, whereas only not-significant changes were found for all Homer isoforms, as judged by RT-qPCR analysis. Thus, muscle-specific changes, myofiber properties, and neuromuscular signaling mechanisms share causal relationships, as highlighted by the variable subcellular Homer isoform expression at the instable NMJs of vestibular lesioned het−/− mice.
Increased Homer Activity and NMJ Localization in the Vestibular Lesion het−/− Mouse soleus Muscle
Volpe, PompeoWriting – Review & Editing
;
2024
Abstract
We investigated the shuttling of Homer protein isoforms identified in soluble (cytosolic) vs. insoluble (membrane–cytoskeletal) fraction and Homer protein–protein interaction/activation in the deep postural calf soleus (SOL) and non-postural gastrocnemius (GAS) muscles of het−/− mice, i.e., mice with an autosomal recessive variant responsible for a vestibular disorder, in order to further elucidate a) the underlying mechanisms of disrupted vestibular system-derived modulation on skeletal muscle, and b) molecular signaling at respective neuromuscular synapses. Heterozygote mice muscles served as the control (CTR). An increase in Homer cross-linking capacity was present in the SOL muscle of het−/− mice as a compensatory mechanism for the altered vestibule system function. Indeed, in both fractions, different Homer immunoreactive bands were detectable, as were Homer monomers (~43–48 kDa), Homer dimers (~100 kDa), and several other Homer multimer bands (>150 kDA). The het−/− GAS particulate fraction showed no Homer dimers vs. SOL. The het−/− SOL soluble fraction showed a twofold increase (+117%, p ≤ 0.0004) in Homer dimers and multimers. Homer monomers were completely absent from the SOL independent of the animals studied, suggesting muscle-specific changes in Homer monomer vs. dimer expression in the postural SOL vs. the non-postural GAS muscles. A morphological assessment showed an increase (+14%, p ≤ 0.0001) in slow/type-I myofiber cross-sectional area in the SOL of het−/− vs. CTR mice. Homer subcellular immuno-localization at the neuromuscular junction (NMJ) showed an altered expression in the SOL of het−/−mice, whereas only not-significant changes were found for all Homer isoforms, as judged by RT-qPCR analysis. Thus, muscle-specific changes, myofiber properties, and neuromuscular signaling mechanisms share causal relationships, as highlighted by the variable subcellular Homer isoform expression at the instable NMJs of vestibular lesioned het−/− mice.File | Dimensione | Formato | |
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