No abstract

Rationale: Activated cardiac fibroblasts (CF) are crucial players in the cardiac damage response; excess fibrosis, however, may result in myocardial stiffening and heart failure development. Inhibition of activated CF has been suggested as a therapeutic strategy in cardiac disease, but whether this truly improves cardiac function is unclear. Objective: To study the effect of CF ablation on cardiac remodeling. Methods and Results: We characterized subgroups of murine CF by single-cell expression analysis and identified periostin as the marker showing the highest correlation to an activated CF phenotype. We generated bacterial artificial chromosome–transgenic mice allowing tamoxifen-inducible Cre expression in periostin-positive cells as well as their diphtheria toxin-mediated ablation. In the healthy heart, periostin expression was restricted to valvular fibroblasts; ablation of this population did not affect cardiac function. After chronic angiotensin II exposure, ablation of activated CF resulted in significantly reduced cardiac fibrosis and improved cardiac function. After myocardial infarction, ablation of periostin-expressing CF resulted in reduced fibrosis without compromising scar stability, and cardiac function was significantly improved. Single-cell transcriptional analysis revealed reduced CF activation but increased expression of prohypertrophic factors in cardiac macrophages and cardiomyocytes, resulting in localized cardiomyocyte hypertrophy. Conclusions: Modulation of the activated CF population is a promising approach to prevent adverse cardiac remodeling in response to angiotensin II and after myocardial infarction.

The rod cGMP-gated channel is localized in the plasma membrane of rod photoreceptor outer segments, where it plays a central role in phototransduction. It consists of ␣-and ␤-subunits that assemble into a heterotetrameric protein. Each subunit contains structural features characteristic of nucleotide-gated channels, including a cGMP-binding domain, multiple membranespanning segments, and a pore region. In addition, the ␤-subunit has a large glutamic acid-and proline-rich region called GARP that is also expressed as two soluble protein variants. Using monoclonal antibodies in conjunction with immunoprecipitation, cross-linking, and electrophoretic techniques, we show that the cGMPgated channel associates with the Na/Ca-K exchanger in the rod outer segment plasma membrane. This complex and soluble GARP proteins also interact with peripherin-2 oligomers in the rim region of outer segment disc membranes. These results suggest that channel/peripherin protein interactions mediated by the GARP part of the channel ␤-subunit play a role in connecting the rim region of discs to the plasma membrane and in anchoring the channel⅐exchanger complex in the rod outer segment plasma membrane.The outer segment is a unique cellular compartment of vertebrate rod and cone photoreceptors where light is captured and converted to an electrical signal as the primary step in the visual process. The rod outer segment (ROS) 1 consists of a highly ordered, axial array of hundreds of discs that is enclosed by a separate plasma membrane. Each disc consists of two, closely spaced, flattened membranes circumscribed by a specialized hairpin loop called the disc rim region. The perimeter of the discs is interrupted by one or more incisures that penetrate toward the center of the disc.The protein composition of the ROS plasma membrane differs from that of the disc membranes (1). The plasma membrane contains the cGMP-gated channel (2), the Na/Ca-K exchanger (3), the GLUT-1 glucose transporter (4), and other membrane proteins, whereas disc membranes contain peripherin-2 (also known as peripherin/Rds) (5), Rom-1 (6), the retinal ATP-binding cassette transporter ABCR (also known as the rim protein) (7,8), and guanylate cyclase (9). Peripherin-2 and Rom-1, homologous subunits that assemble as oligomeric complexes (10, 11), and ABCR are restricted to the rim and incisures of disc membranes (5,7,8,12). Rhodopsin, the major membrane protein of rod outer segments, is present in both the flattened (lamellar) region of disc membranes and the plasma membrane. The molecular mechanisms responsible for the targeting of specific proteins to the disc and plasma membrane and protein/protein interactions involved in the formation and stabilization of the unique ROS structure are not known. The cGMP-gated channel of photoreceptors plays a central role in phototransduction by controlling the flow of cations into the outer segment in response to light-mediated changes in intracellular cGMP. The rod channel consists of two homologous subunits termed ␣ and ␤ that assemble...