In general, NOS-derived NO could regulate a wide range of cell functions including inflammation, apoptosis, permeability and cell growth. The NOS may be localized mainly near specific intracellular membrane domains including the cytoplasmic face of the Golgi apparatus and plasma membrane caveolae [
41]. Caveolae are specialized lipid domains of the plasma membrane containing caveolins, which are key structural components and serve as a scaffold for signaling proteins [
42]. In addition, caveolae can classify signal transduction molecules which regulate multiple functions including the production of nitric oxide (NO) by the caveolae resident enzyme NOS [
43]. Flask-shaped invaginations of the plasma membrane known as caveolae could work as critical regulators for human health and/or disease [
44].
(Figure 2) The integral membrane protein caveolin-1 (CAV1) is a major structural component of caveolae and is required in place of caveolae formation in non-muscle cells [
45]. Association of CAV1 into oligomeric protein complexes is an indispensable step in caveolae biogenesis, and faults in the oligomerization could cause several diseases [
46]. In mammals, CAV1 and/or caveolae are widely distributed in many tissues where they operate for lipid homeostasis, protection, endocytosis, and signal transduction [
47]. Conversely, dysregulation of caveolae may contribute to the development/progression of several diseases including cancers, inflammatory respiratory diseases, hypertension, asthma, and lipodystrophy [
48]. Interestingly, the P132L mutation of wild type CAV1 has been identified in several different patient samples including breast cancer and/or lung adenocarcinomas [
49]. In addition to the P132L mutation, a variety of other pathogenic mutations in caveolin homologs have been identified in humans [
50]. The P132L mutation has also been reported to disturb the ability of CAV1 to correctly move to the plasma membrane, suggesting it might function as a dominant negative with the wild type CAV1 [
51]. These findings emphasize the importance of P132 mutation in caveolin also function in the development/progression of health and disease. Therefore, the P132L mutation is also a powerful tool to investigate how defects in trafficking and/or oligomerization of caveolins could impede the caveolae formation [
52]. Some protein mutations that could lead to muscular dystrophy may often generate deficiencies in cytoskeletal support of the muscle sarcolemma. In particular, caveolae are cholesterol-rich microdomains that could construct mechanically deformable invaginations of the sarcolemma. For example, it is well-known that mutations to caveolin-3, the main scaffolding protein of caveolae in muscle, can trigger limb-girdle muscular dystrophy (LGMD). An equivalent mutation in caveolin-3 (CAV3), P105L (curiously denoted as P104L in many studies), could show the phenotype of muscular dystrophies both in humans and/or animal models [
53]. Therefore, the most equivalent to P132L may be the P105L mutation of CAV3 frequently associated with LGMD [
54,
55]. As for dominant negative function, muscle biopsies from patients harboring the P105L mutation of CAV3 with an autosomal form of limb-girdle muscular dystrophy may detect noticeably decreased CAV3 levels compared to normal controls [
55]. In addition, oligomerization and/or trafficking defects have been also observed for the P105L mutants of CAV3 [
56]. Resembling the P132L mutation of CAV1, the P105L mutant protein can intracellularly entrap the wild type CAV3 in mammalian heterologous expression systems [
57]. However, the fine character of the oligomerization defects appears to be slightly different, as P105L mutation of CAV3 may incline to form larger oligomers rather than wild type CAV3 [
56,
58]. It seems possible that the P105L mutation of CAV3 may play a comparable role in destabilizing the structure of CAV3 complexes, as is the situation for CAV1 [
59]. Standard expression levels of CAV3 may be protective for the sarcolemma, while the upregulation of CAV3 may be detected in several muscular dystrophies owing to the probable compensation for additional functional deficiencies [
60].