Introduction: Following cardiac pressure overload, the crosstalk of fibroblasts, myocytes and immune cells like cardiac resident macrophages (crMPs) is pivotal for the adaptive processes within the myocardium. crMPs constitute up to 5% of cells in the murine heart and were shown to play key roles in cardiac homeostasis, however, little is known about the regulative mechanisms of long non-coding RNAs (lncRNA) in modulating macrophage function. Previous data from our lab led to the identification of a conserved, macrophage enriched lncRNA named Schlafenlnc, that is upregulated during cardiac pressure overload in mice. Additionally, in vitro experiments have shown a reduction in adhesion and chemotactic migration in Schlafenlnc deficient macrophages.

Objective: Determining regulative functions of the lncRNA Schlafenlnc in cardiac resident macrophages in state of health and disease.

Methods and Materials: To study the function of Schlafenlnc in vivo, a global knockout mouse line was generated. Schlafenlnc -/- and +/+ mice from heterozygous breeding were subjected to pressure overload of the left ventricle (transverse aortic constriction, TAC). This model leads to an inflammatory response, severe hypertrophy of the left ventricle and eventually development of fibrosis. Cardiac function was assessed using high resolution echocardiography (Vevo Visual Sonics Ultrasound Device), tissue sections were stained for CD68 to quantify macrophages and fibrosis was measured by means of Sirius Red. Following CD45+ purification using MACS, droplet-based single cell sequencing was performed (Chromium Next GEM Single Cell 3’ v3.1).

Results: Overall heart weight was significantly decreased in Schlafenlnc-/- mice after 6 days of TAC compared to the wildtype control. Simultaneously, an ameliorated ejection fraction in Schlafenlnc-/- mice was observed. Also, composition of the ventricular tissue was altered as fibrosis was shown to develop less in Schlafenlnc-/- mice. A striking 5-fold reduced macrophage infiltration 6 days after TAC in Schlafenlnc-/- mice was shown by immunofluorescence. As this indicates a potential migration defect in Schlafenlnc-/- crMPs further research on this finding is ongoing. Along the line of our in vitro data, single-cell sequencing data of the Schlafenlnc KO exhibits a significant downregulation of pathways associated with migration and adhesion of Schlafenlnc-/- crMPs after 6d of TAC compared to litter mate wildtype controls.

Conclusion: In this study, Schlafenlnc was identified as an important regulator of inflammatory processes in the heart. As the loss-of-function of this conserved lncRNA was beneficial in disease, its inhibition in human patients might be a potential therapeutic approach to ameliorate inflammation in the heart.