Pathogenic Potential of Hic1-Expressing Cardiac Stromal Progenitors.

The cardiac stroma contains multipotent mesenchymal progenitors. However, lineage relationships within cardiac stromal cells are poorly defined. Here, we identified heart-resident PDGFRa+ SCA-1+ cells as cardiac fibro/adipogenic progenitors (cFAPs) and show that they respond to ischemic damage by generating fibrogenic cells. Pharmacological blockade of this differentiation step with an anti-fibrotic tyrosine kinase inhibitor decreases post-myocardial infarction (post-MI) remodeling and leads to improvement in cardiac function. In the undamaged heart, activation of cFAPs through lineage-specific deletion of the gene encoding the quiescence-associated factor HIC1 reveals additional pathogenic potential, causing fibrofatty infiltration within the myocardium and driving major pathological features pathognomonic in arrhythmogenic cardiomyopathy (AC). In this regard, cFAPs contribute to multiple pathogenic cell types within cardiac tissue and therapeutic strategies aimed at modifying their activity are expected to have tremendous benefit for the treatment of diverse cardiac diseases.

Collision or convergence?: beliefs and politics in neuroscience discovery, ethics, and intervention.

Discovery and interventions for neurological disorders have a unique capacity to galvanize public opinion over issues of access, human rights, decision making, and the definition of disease. Here we highlight five cases where beliefs and politics prevailed over evidence and ethics. We examine lessons from them about the communication of risk and the power of public influence on science, society, and policy.

In vivo characterization of neural crest-derived fibro/adipogenic progenitor cells as a likely cellular substrate for craniofacial fibrofatty infiltrating disorders.

The cellular substrate underlying aberrant craniofacial connective tissue accumulation that occurs in disorders such as congenital infiltration of the face (CILF) remain elusive. Here we analyze the in vivo properties of a recently identified population of neural crest-derived CD31-:CD45-:alpha7-:Sca1+:PDGFRa+ fibro/adipogenic progenitors (NCFAPs). In serial transplantation experiments in which NCFAPs were prospectively purified and transplanted into wild type mice, NCFAPs were found to be capable of self-renewal while keeping their adipogenic potential. NCFAPs constitute the main responsive FAP fraction following acute masseter muscle damage, surpassing the number of mesoderm-derived FAPs (MFAPs) during the regenerative response. Lastly, NCFAPs differentiate into adipocytes during muscle regeneration in response to pro-adipogenic systemic cues. Altogether our data indicate that NCFAPs are a population of stem/primitive progenitor cells primarily involved in craniofacial muscle regeneration that can cause tissue degeneration when the damage co-occurs with an obesity inducing diet.

Tissue-resident Sca1+ PDGFRα+ mesenchymal progenitors are the cellular source of fibrofatty infiltration in arrhythmogenic cardiomyopathy.

Arrhythmogenic cardiomyopathy (AC) is a disease of the heart involving myocardial dystrophy leading to fibrofatty scarring of the myocardium and is associated with an increased risk of both ventricular arrhythmias and sudden cardiac death. It often affects the right ventricle but may also involve the left. Although there has been significant progress in understanding the role of underlying desmosomal genetic defects in AC, there is still a lack of data regarding the cellular processes involved in its progression. The development of cardiac fibrofatty scarring is known to be a principal pathological process associated with ventricular arrhythmias, and it is vital that we elucidate the role of various cell populations involved in the disease if targeted therapeutics are to be developed. The known role of mesenchymal progenitor cells in the reparative process of both the heart and skeletal muscle has provided inspiration for the identification of the cellular basis of fibrofatty infiltration in AC. Here we hypothesize that reparative processes triggered by myocardial degeneration lead to the differentiation of tissue-resident Sca1+ PDGFRα+ mesenchymal progenitors into adipocytes and fibroblasts, which compose the fibrofatty lesions characteristic of AC.

Nonmyogenic cells in skeletal muscle regeneration.

Although classical dogma dictates that satellite cells are the primary cell type involved in skeletal muscle regeneration, alternative cell types such as a variety of inflammatory and stromal cells are also actively involved in this process. A model describing myogenic cells as direct contributors to regeneration and nonmyogenic cells from other developmental sources as important accessories has emerged, with similar systems having been described in numerous other tissues in the body. Increasing evidence supports the notion that inflammatory cells function as supportive accessory cells, and are not merely involved in clearing damage following skeletal muscle injury. Additionally, recent studies have highlighted the role of tissue resident mesenchymal cell populations as playing a central role in regulating regeneration. These "accessory" cell populations are proposed to influence myogenesis via direct cell contact and secretion of paracrine trophic factors. The basic foundations of accessory cell understanding should be recognized as a crucial component to all prospects of regenerative medicine, and this chapter intends to provide a comprehensive background on the current literature describing immune and tissue-resident mesenchymal cells' role in skeletal muscle regeneration.

Actin cytoskeleton dynamics promotes leptin-induced vascular smooth muscle hypertrophy via RhoA/ROCK- and phosphatidylinositol 3-kinase/protein kinase B-dependent pathways.

Obesity is associated with increased leptin production that may contribute to cardiovascular pathology through a multiplicity of effects. Leptin has been shown to contribute to vascular remodeling through various mechanisms, including production of vascular smooth muscle (VSMC) hypertrophy; however, the mechanisms underlying the vascular hypertrophic effect of leptin remain unknown. In the present study, we investigated the contributions of the RhoA/Rho kinase (ROCK) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathways, actin dynamics, and the expression of serum-response factor (SRF) in the hypertrophic effects of leptin on vascular tissue. Strips of rat portal vein (RPV) were cultured with or without leptin at 3.1 nM for 1 to 3 days. Leptin significantly increased RhoA activity by 163 +/- 20%, whereas phosphorylation of downstream factors, including LIM kinase 1 and cofilin-2, was increased by 160 +/- 25 and 290 +/- 25%, respectively. Leptin also significantly phosphorylated Akt by 130 +/- 30%, which was inhibited by the PI3K inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). RhoA/ROCK and PI3K/Akt activation was associated with a significant increase in RPV wet weight (11 +/- 1%), protein synthesis (45 +/- 7%), SRF expression (136 +/- 11%), and polymerization of actin, as reflected by an increase in the F-/G-actin ratio, effects that were significantly attenuated by a leptin receptor (leptin obese receptor) antibody, the ROCK inhibitor (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) (Y-27632) as well as the PI3K inhibitor LY294002. Our results indicate that the activation of RhoA/ROCK and PI3K/Akt plays a pivotal role in leptin signaling, leading to the development of VSMC hypertrophy through a mechanism involving altered actin dynamics.

Inhibition of fatty acid amide hydrolase, a key endocannabinoid metabolizing enzyme, by analogues of ibuprofen and indomethacin.

There is evidence in the literature that the nonsteroidal anti-inflammatory drugs indomethacin and ibuprofen can interact with the cannabinoid system both in vitro and in vivo. In the present study, a series of analogues of ibuprofen and indomethacin have been investigated with respect to their ability to inhibit fatty acid amide hydrolase, the enzyme responsible for the hydrolysis of the endogenous cannabinoid anandamide. Of the fourteen compounds tested, the 6-methyl-pyridin-2-yl analogue of ibuprofen ("ibu-am5") was selected for further study. This compound inhibited rat brain anandamide hydrolysis in a non-competitive manner, with IC50 values of 4.7 and 2.5 microM being found at pH 6 and 8, respectively. By comparison, the IC50 values for ibuprofen were 130 and 750 microM at pH 6 and 8, respectively. There was no measurable N-acylethanolamine hydrolyzing acid amidase activity in rat brain membrane preparations. In intact C6 glioma cells, ibu-am5 inhibited the hydrolysis of anandamide with an IC50 value of 1.2 microM. There was little difference in the potencies of ibu-am5 and ibuprofen towards cyclooxygenase-1 and -2 enzymes, and neither compound inhibited the activity of monoacylglycerol lipase. Ibu-am5 inhibited the binding of [3H]-CP55,940 to rat brain CB1 and human CB2 cannabinoid receptors more potently than ibuprofen, but the increase in potency was less than the corresponding increase in potency seen for inhibition of FAAH activity. It is concluded that ibu-am5 is an analogue of ibuprofen with a greater potency towards fatty acid amide hydrolase but with a similar cyclooxygenase inhibitory profile, and may be useful for the study of the therapeutic potential of combined fatty acid amide hydrolase-cyclooxygenase inhibitors.

The potency of the fatty acid amide hydrolase inhibitor URB597 is dependent upon the assay pH.

Inhibitors of the enzyme fatty acid amide hydrolase (FAAH), the principal enzyme involved in the metabolism of the endogenous cannabinoid anandamide, have potential utility in the treatment of disorders including inflammation and inflammatory pain. The carbamate compound URB597 (3'-carbamoyl-biphenyl-3-yl-cyclohexylcarbamate) potently and selectively inhibits FAAH by forming a covalent bond with a key serine residue of the enzyme. Little is known as to the pH dependency of this inhibition. Using a preincubation time of 10min, URB597 inhibited rat brain anandamide hydrolysis with pI(50) values of 7.19+/-0.02 and 7.75+/-0.06 at pH 6 and 8, respectively. The inhibition was time-dependent, and second order rate constants of approximately 0.15x10(6)M(-1)min(-1) (pH 6) and approximately 1.2x10(6)M(-1)min(-1) (pH 8) could be estimated. In intact C6 glioma cells and using a preincubation time of 10min, URB597 inhibited the hydrolysis of 250nM [(3)H]AEA hydrolysis with pI(50) values of 5.58+/-0.07 and 6.45+/-0.07 at extracellular pH values of 6 and 8, respectively. Since tissue pH is affected by inflammation, these data would suggest that the pH selectivity of the inhibition can contribute to the potency of the compound in vivo.