Matrix regeneration proteins in the hypoxia-triggered exosomes of shoulder tenocytes and adipose-derived mesenchymal stem cells

Regenerative functions of exosomes rely on their contents which are influenced by pathological stimuli, including hypoxia, in rotator cuff tendon injuries (RCTI). The hypoxic environment triggers tenocytes and adjacent adipose-derived mesenchymal stem cells (ADMSCs) to release regenerative mediators to the ECM via the exosomes which elicit autocrine/paracrine responses to protect the tendon matrix from injury. We investigated the exosomal protein contents from tenocytes and subcutaneous ADMSCs from the shoulder of Yucatan microswine cultured under hypoxic conditions (2% O₂). The exosomal proteins were detected using high-resolution mass spectrometry nano-LC-MS/MS Tribrid system and were compiled using 'Scaffold' software. Hypoxic exosomes from tenocytes and ADMSCs carried 199 and 65 proteins, respectively. The key proteins identified by mass spectrometry and associated with ECM homeostasis from hypoxic ADMSCs included MMP2, COL6A, CTSD and TN-C and those from hypoxic tenocytes were THSB1, NSEP1, ITIH4 and TN-C. These findings were confirmed at the mRNA and protein level in the hypoxic ADMSCs and tenocytes. These proteins are involved in multiple signaling pathways of ECM repair/regeneration. This warrants further investigations for their translational significance in the management of RCTI.

Therapeutic potential of exosomes in rotator cuff tendon healing

Rotator cuff tears are common musculoskeletal injuries that can cause significant pain and disability. While the clinical results of rotator cuff repair can be good, failure of tendon healing remains a significant problem. Molecular mechanisms underlying structural failure following surgical repair remain unclear. Histologically, enhanced inflammation, disorganization of the collagen fibers, calcification, apoptosis and tissue necrosis affect the normal healing process. Mesenchymal stem cells (MSCs) have the ability to provide improved healing following rotator cuff repair via the release of mediators from secreted 30-100 nm extracellular vesicles called exosomes. They carry regulatory proteins, mRNA and miRNA and have the ability to increase collagen synthesis and angiogenesis through increased expression of mRNA and release of proangiogenic factors and regulatory proteins that play a major role in proper tissue remodeling and preventing extracellular matrix degradation. Various studies have shown the effect of exosomes on improving outcome of cutaneous wound healing, scar tissue formation, degenerative bone disease and Duchenne Muscular Dystrophy. In this article, we critically reviewed the potential role of exosomes in tendon regeneration and propose the novel use of exosomes alone or seeded onto biomaterial matrices to stimulate secretion of favorable cellular factors in accelerating the healing response following rotator cuff repair.

Genes interconnecting AMPK and TREM-1 and associated microRNAs in rotator cuff tendon injury

Fatty infiltration and inflammation delay the healing responses and raise major concerns in the therapeutic management of rotator cuff tendon injuries (RCTI). Our evaluations showed the upregulation of 'metabolic check point' AMPK and inflammatory molecule, TREM-1 from shoulder biceps tendons collected from RCTI subjects. However, the epigenetic regulation of these biomolecules by miRNAs is largely unknown and it is likely that a deeper understanding of the mechanism of action can have therapeutic potential for RCTI. Based on this background, we have evaluated the miRNAs from RCTI patients with fatty infiltration and inflammation (FI group) and compared with RCTI patients without fatty infiltration and inflammation (No-FI group). NetworkAnalyst was employed to evaluate the genes interconnecting AMPK and TREM-1 pathway, using PRKAA1 (AMPK), TREM-1, HIF1α, HMGB1, and AGER as input genes. The most relevant miRNAs were screened by considering the fold change below - 7.5 and the number of target genes 10 and more which showed 13 miRNAs and 216 target genes. The exact role of these miRNAs in the fatty infiltration and inflammation associated with RCTI is still unknown and the understanding of biological activity of these miRNAs can pave ways to develop miRNA-based therapeutics in the management of RCTI.

Amplification of Mitochondrial Activity in the Healing Response Following Rotator Cuff Tendon Injury

Mitochondrial function following rotator cuff tendon injury (RCI) influences the tendon healing. We examined the mitochondrial morphology and function under hypoxia in the shoulder tendon tissue from surgically-induced tenotomy-RCI rat model and cultured swine tenocytes. The tendon tissue was collected post-injury on 3-5 (Group-A), 10-12 (Group-B), and 22-24 (Group-C), days and the corresponding contralateral tendons were used as control for each group. There was higher protein expression of citrate synthase (P < 0.0001) [10.22 MFI (mean fluorescent intensity)] and complex-1 (P = 0.0008) (7.86 MFI) in Group-A and Group-B that decreased in Group-C [(P = 0.0201) (5.78 MFI and (P = 0.7915) (2.32 MFI), respectively] compared to control tendons. The ratio of BAX:Bcl2 (Bcl2 associated x protein:B cell lymphoma 2) in RCI tendons increased by 50.5% (Group-A) and 68.4% (Group-B) and decreased by 25.8% (Group-C) compared to normoxic controls. Hypoxia increased β-tubulin expression (P = 0067) and reduced PGC1-α (P = 0412) expression in the isolated swine tenocytes with no effect on the protein expression of Complex-1 (P = 7409) and citrate synthase (P = 0.3290). Also, the hypoxic tenocytes exhibited about 4-fold increase in mitochondrial superoxide (P < 0.0001), altered morphology and mitochondrial pore integrity, and increase in mitochondrial density compared to normoxic controls. These findings suggest the critical role of mitochondria in the RCI healing response.

Controversial topics in shoulder arthroscopy

This is a review of the symposium entitled Controversial Topics in Shoulder Arthroscopy 2001, presented at the Arthroscopy Association of North America 20th Annual Meeting in Seattle, Washington in April of 2001. The covered topics include micro-instability, partial thickness rotator cuff tears, pathology of the biceps tendon, and thermal capsulorrhaphy.

Incidence of acromioclavicular joint complications after arthroscopic subacromial decompression

We performed a chart and radiograph review of 173 patients (183 shoulders) who underwent arthroscopic subacromial decompression between 1991 and 1994 and had preoperative and postoperative radiographs. The study focused on the presence of preoperative acromioclavicular joint pathology, intraoperative violation of the acromioclavicular joint, extent of distal clavicle excision, and subsequent development of acromioclavicular joint symptoms. The 183 surgical procedures were divided into three groups: shoulders with subacromial decompression without acromioclavicular joint violation (103 of 183; 56%; group A); shoulders with subacromial decompression with acromioclavicular joint violation and partial distal clavicle resection (36 of 183; 20%; group B); and shoulders with subacromial decompression with complete distal clavicle resection (44 of 183; 24%; group C). Groups A and C had no postoperative sequelae in reference to the acromioclavicular joint. In contrast, 14 of the 36 shoulders (39%) in group B with a documented acromioclavicular joint violation and a partial distal clavicle resection developed acromioclavicular joint symptoms at an average of 8.4 months (range, 1.8 to 19 months) after surgery. This finding was statistically significant (P=.0001). The results of this study suggest that any violation of the acromioclavicular joint in the course of an arthroscopic subacromial decompression may jeopardize the result. The degree of violation is not helpful in predicting outcome. As a result of this study, we suggest an all-or-none surgical approach to the acromioclavicular joint and distal clavicle resection.

Captured shoulder: a complication of rotator cuff surgery

Thirteen patients who developed restrictive subdeltoid adhesions after rotator cuff repair were identified. These patients underwent second-look arthroscopy and takedown of adhesions at an average of 37 weeks after their index surgery. Clinical findings include pain and restricted motion that does not yield to manipulation under anesthesia. Arthroscopic findings are subdeltoid adhesions and a chondral lesion (companion lesion) of the humeral head articular surface. Patients were reevaluated at 26 weeks after their release of adhesions. Prerelease and postrelease University of California, Los Angeles (UCLA) scores average 14.8 and 30.1, respectively. Prerelease and postrelease UCLA pain scores averaged 2.6 and 7.7, respectively. Prerelease and postrelease range of motion was as follows: Flexion, 141/158; abduction, 123/141; internal rotation, 47/69; and external rotation, 53/74. The authors have proposed a theory to explain the clinical and arthroscopic findings in this subgroup of patients who are dissatisfied after rotator cuff repair. A technique for and the results of release of the subdeltoid adhesions also are reported.

Arthroscopy. Basic setup and equipment

Shoulder arthroscopy necessitates attention to detail. Adopting a comfortable setup that includes a plan for every detail, including the surgeon's position, the patient's position, the draping techniques, and the types of fluid and equipment necessary, adds to the smooth flow of the operation even when the surgical plan changes. I have described my method of basic arthroscopic setup and equipment, which has helped me to deal with the many frustrations faced during arthroscopy on the shoulder. It is hoped this article may enable the reader to avoid some of these problems if this or a similar basic setup is adopted.

Arthroscopic shoulder capsulorraphy: does it work?

The purpose of this project was to answer the question, "Can shoulder instability be dealt with safely and effectively arthroscopically?" This study, which began in December 1982 and concluded in February 1985, involved 12 patients, 3 females and 9 males whose ages ranged from 14 to 40 years. Followup ranged from 31 to 63 months, the average being 44.8 months. The arthroscopic procedure was based on the use of a tool designed to capture the capsule, thus allowing placement of either one or two low profile extraarticular staples in the capsule. Two cases were failures. The remaining 10 patients were pleased with their operation. Based on the classification of Rowe et al., functional results were six excellent, two good, two fair, and two poor. The six patients with excellent results had shoulders of normal appearance. They were fully active and had neither pain nor limitation of motion. All six patients had negative apprehension signs. The two patients with good results had similar outcomes, but they had occasional morning stiffness and intermittent mild pain, as well as a 10 degrees limitation of external rotation in both adduction and abduction. One patient who had a fair result had a positive apprehension sign and occasional pain with quick motion. The other patient with a fair result was hampered by more significant pain on an intermittent basis, yet the pain was not a constant issue. None of these patients had radiographic evidence of increased degenerative changes of the shoulder or staple migration. There were two complications and two failures.(ABSTRACT TRUNCATED AT 250 WORDS)

Shoulder arthroscopy: a modified approach

This paper proposes a modification of the classical position for shoulder arthroscopy. Two changes are proposed to improve visualization, accentuate pathology, and give better access to the inferior one half to one third of the shoulder joint. The direct lateral position is changed to a semilateral position in which the patient is allowed to rotate 30 to 40 degrees posteriorly, thus putting the shoulder joint on a horizontal plane. This allows for more comfortable arthroscopy and instrumentation. Also, if capsulorrhaphy is desired, better penetration of the scapula is possible since the scapula is vertical; thus, the angle of the approaching staple is less severe. The second change is to apply traction in a plane perpendicular to the long axis of the humerus rather than parallel to it. This modification elevates the humerus out of the glenoid rather than distracts the humerus into a subluxed position. The result accentuates labral pathology and gives a significantly improved view of the inferior one half to one third of the glenoid capsule. This new plane of traction allows excellent visualization with very little traction; thus, the problem of traction neuropraxia has been eliminated.