The effect of cellular nuclear function alteration on the pathogenesis of shoulder adhesive capsulitis: an immunohistochemical study on lamin A/C expression

Background: The network of intermediate filament proteins underlying the inner nuclear membrane forms the nuclear lamina. Lamins have been associated with important cellular functions: DNA replication, chromatin organization, differentiation of the cell, apoptosis and in maintenance of nuclear structure. Little is known regarding the etiopathogenesis of adhesive capsulitis (AC); recently, a dysregulating fibrotic response starting from a subpopulation has been described within the fibroblast compartment, which suddenly turns on an activated phenotype. Considering the key role of A-type lamins in the regulation of cellular stability and function, our aim was to compare the lamin A/C expression between patients with AC and healthy controls. Materials and methods: A case–control study was performed between January 2020 and December 2021. Tissue samples excised from the rotator interval were analysed for lamin A/C expression by immunohistochemistry. Patients with AC were arbitrarily distinguished according to the severity of shoulder flexion limitation: ≥ 90° and < 90°. Controls were represented by samples obtained by normal rotator interval excised from patients submitted to shoulder surgery. The intensity of staining was graded, and an H-score was assigned. Statistical analysis was performed (Chi-square analysis; significance was set at alpha = 0.05). Results: We enrolled 26 patients [12 male and 14 female, mean age (SD): 52.3 (6.08)] and 15 controls [6 male and 9 female, mean age (SD): 57.1 (5.3)]. The expression of lamin A/C was found to be significantly lower in the fibroblasts of patients with adhesive capsulitis when compared with controls (intensity of staining: p: 0.005; H-score: 0.034); no differences were found regarding the synoviocytes (p: > 0.05). Considering only patients with AC, lamin A/C intensity staining was found to be significantly higher in samples where acute inflammatory infiltrate was detected (p: 0.004). No significant changes in levels of lamin A/C expression were documented between the mild and severe adhesive capsulitis severity groups. Conclusions: Our study demonstrated that the activity of lamin A/C in maintaining nuclear structural integrity and cell viability is decreased in patients with adhesive capsulitis. The phase of the pathogenetic process (freezing and early frozen) is the key factor for cell functionality. On the contrary, the clinical severity of adhesive capsulitis plays a marginal role in nuclear stability. Level of evidence: III.