Adiponectin secretion from cardiomyocytes produces canonical multimers and partial co-localization with calsequestrin in junctional SR

• Published in: Molecular and cellular biochemistry 2019-07, Vol.457 (1-2), p.201-214
• Main Authors: Solarewicz, Joanna, Manly, Amanda, Kokoszka, Stephanie, Sleiman, Naama, Leff, Todd, Cala, Steven
• Format: Article
• Language: English
• Subjects: Adenoviruses; Adipocytes; Adiponectin; Adiponectin - metabolism; Animals; Biochemistry; Biomedical and Life Sciences; Calcium ions; Calcium sequestration; Calcium-binding proteins; Calsequestrin; Calsequestrin - metabolism; Canonical forms; Cardiology; Cardiomyocytes; Cell lines; Cercopithecus aethiops; Compartments; COS Cells; Ethylenediaminetetraacetic acid; Fat metabolism; Golgi apparatus; Heart cells; HEK293 Cells; Hexamers; Humans; Life Sciences; Localization; Medical Biochemistry; Metabolism; Molecular structure; Molecular weight; Myocytes, Cardiac - metabolism; Oncology; Physiological aspects; Protein Multimerization; Protein Transport; Proteins; Rats; Rats, Sprague-Dawley; Sarcomeres; Sarcoplasmic reticulum; Sarcoplasmic Reticulum - metabolism; Secretion; Substructures; Translocation; Trimers; Tubules
• ISSN: 0300-8177; 1573-4919
• DOI: 10.1007/s11010-019-03524-9

Adiponectin (ADN) is an abundant protein in serum, secreted by adipocytes, that acts as a signal for fat metabolism. It is marked by a complex molecular structure that results from processes within the secretory pathway, producing a canonical set of multimers. ADN may also be secreted from cardiomyocytes, where a unique sarcomeric endoplasmic/sarcoplasmic reticulum (ER/SR) substructure has been characterized primarily for its Ca handling. We expressed ADN in cultured primary adult cardiomyocytes and nonmuscle (COS) cells. After 48 h of ADN expression by adenovirus treatment, roughly half of synthesized ADN was secreted from cardiomyocytes, and half was still in-transit within inner membrane compartments, similar to COS cells. Cardiomyocytes and COS cells both produced ADN in the three canonical forms: trimers, hexamers, and 18-mers. Higher rates of secretion occurred for higher-molecular weight multimers, especially 18-mers. The highest levels of ADN protein, whether in transit or secreted, were present as trimers and hexamers. In nonmuscle cell lines, ADN trafficked through ER and Golgi compartments as expected. In contrast, ADN in primary adult cardiomyocytes populated ER/SR tubules along the edges of sarcomeres that emanated from nuclear surfaces. Prominent co-localization of ADN occurred with calsequestrin, a marker of junctional SR, the Ca 2+ -release compartment of the cell. The early steps in ADN trafficking re-trace those recently described for newly made junctional SR proteins, involving a nuclear envelope ( NE ) translocation into S R tubules that are oriented along sarcolemmal transverse ( T )-tubules ( NEST pathway).