Background:

Protein kinase C (PKC) isozymes are a family of serine/threonine kinases, which are centrally involved in cardiac growth, hypertrophy, inflammation, fibrosis and survival of cardiac tissue. While most of the reported effects are mediated by PKCα, PKCβ, PKCɣ, PKCδ and PKCε, little is known about the atypical PKCs, PKCζ and PKCι/λ. Here we explored the regulation and role of aPKC in the adult mouse heart.

Methods and results:

Using RNA-seq. and qRT-PCR the expression of PKCζ and PKCλ was analyzed in left ventricular myocardium (LV) of male mice at 3 months  (baseline), at 9-12 months of age (n=7-11) and at 3 months after pressure overload (4 weeks of TAC, n=8) or chronic β-adrenergic stimulation by Isoproterenol (ISO, osmotic minipumps, 45mg/kg/day, 2 weeks, n=11). The expression of PKCζ was barely detectable in all conditions, while PKCλ mRNA was readily expressed without alterations in young (n=8), aged (n=10) or TAC (n=8) WT mouse hearts. ISO induced nuclear translocation of PKCλ in cardiomyocytes and chronic ISO treatment resulted in reduced cardiac PKCλ expression. Mice with cardiomyocyte-specific deletion of PKCλ (PKCλ-CKO) developed aged-related heart failure (fractional shortening (FS): 18% vs. 34% in WT, p<0.01) with increased mortality (27% vs. 11% in WT) associated with increased expression of fibrosis- (collagen 1a1: 2.4-fold, p<0.05) and inflammation markers (adhesion G protein-coupled receptor E1: 1.8-fold, p<0.01). TAC had no specific effect in PKCλ-CKO which developed similar hypertrophy and cardiac dysfunction as WT mice while chronic ISO infusion induced heart failure in PKCλ-CKO (FS: 25% vs. 30% in WT, p<0.01).
RNAseq analyses revealed 34 differentially regulated genes (p-adj. <0.05) with 13 up- and 21 downregulated in 3-months old PKCλ-CKO compared to WT mice. Among them, a marked downregulation of myotilin (MYOT, -50%, p<0.01), a known disease gene for limb girdle muscular dystrophy and a downregulation of striatin (STRN, -32%, p<0.01), for which is known that a knockdown reduces cardiomyocyte contraction rate.

Conclusion:

The present study shows that from the two aPKC isoenzymes only PKCλ is substantially expressed in the adult mouse heart. Cardiomyocyte deficiency of PKCλ caused age-related heart failure and heart failure after chronic β-adrenergic activation but not after pressure overload. RNA-Seq. revealed early downregulation of genes associated with myofibrillar myopathy and cardiomyocyte contraction. Thus, PKCλ seems important for protection of the heart from aging and from chronic β-adrenergic activation.