**2.3. Prokineticin in insulin resistance**

The endothelium is essential for insulin transcapillary delivery to the skeletal muscle interstiti‐ um. This process is the rate‐limiting step in insulin‐stimulated glucose uptake. [24] The impair‐ ment ofinsulindeliveryprocess contributes to insulinresistance [25].Onthe otherhand,insulin resistance leads to endothelial dysfunction [26]. Thus, the vascular endothelium is a potential therapeutic target for the prevention of insulin resistance and related complications [27].

Endothelium‐specific PKR1‐knockout mice (PKR1ec*‐*/*‐* ) display impaired capillary formation and low transcapillary insulin uptake [23]. Impaired insulin delivery and signaling in endo‐ thelial cells (ECs) has been observed in cases of insulin resistance with type 2 diabetes and obesity. Endothelial cells overexpressing PKR1 promotes insulin transendothelial uptake [9] and angiogenesis [28]. PKR1*ec‐/‐* mice display lipodystrophy due to poor capillary formation in the AT. Lipodystrophies, involving a loss of WAT, cause hyperphagia and peripheral insulin resistance [29].

As a summary, prokineticin regulates appetite (effects in central nervous system (CNS)) and suppresses adipocyte expansion (direct effect on adipocyte tissue), promotes normal fat stor‐ age (endothelial‐dependent effect) and increases insulin sensitivity. Therapeutic strategies targeting PKR1 could be important to treat obesity and obesity‐associated insulin resistance.

#### **2.4. Prokineticin in cardiovascular regulation**

pocytes), PKR1 suppress the ability of these precursor cells to become adipocytes (**Figure 1**) [7]. The expansion and metabolism of the adipose tissue are the major problem in obesity.

**Figure 1.** Prokineticin‐2/PKR1 signaling may act as a new connector between development of obesity, diabetes and car‐ diovascular diseases. Prokineticin‐2/PKR1 signaling in central nervous system (CNS) regulates food intake. Prokineti‐ cin‐2 released from adipocytes controls preadipocyte conversion to adipocyte via PKR1 signaling. Prokineticin‐2/PKR1 signaling promotes survival of cardiomyocytes and angiogenesis and involved in neovascularization by activating car‐ diac progenitor cells. Prokineticin‐2/PKR1 signaling contributes to heart and kidney development as well as kidney

The endothelium is essential for insulin transcapillary delivery to the skeletal muscle interstiti‐ um. This process is the rate‐limiting step in insulin‐stimulated glucose uptake. [24] The impair‐ ment ofinsulindeliveryprocess contributes to insulinresistance [25].Onthe otherhand,insulin resistance leads to endothelial dysfunction [26]. Thus, the vascular endothelium is a potential therapeutic target for the prevention of insulin resistance and related complications [27].

and low transcapillary insulin uptake [23]. Impaired insulin delivery and signaling in endo‐ thelial cells (ECs) has been observed in cases of insulin resistance with type 2 diabetes and obesity. Endothelial cells overexpressing PKR1 promotes insulin transendothelial uptake [9] and angiogenesis [28]. PKR1*ec‐/‐* mice display lipodystrophy due to poor capillary formation in the AT. Lipodystrophies, involving a loss of WAT, cause hyperphagia and peripheral insulin

As a summary, prokineticin regulates appetite (effects in central nervous system (CNS)) and suppresses adipocyte expansion (direct effect on adipocyte tissue), promotes normal fat stor‐

) display impaired capillary formation

function. Whether this signaling involves heart and kidney regulation through CNS remains to be studied.

**2.3. Prokineticin in insulin resistance**

118 Adiposity - Omics and Molecular Understanding

resistance [29].

Endothelium‐specific PKR1‐knockout mice (PKR1ec*‐*/*‐*

Obesity is both an independent risk factor and a risk marker for the development of asymp‐ tomatic and symptomatic coronary artery disease, heart failure and atrial fibrillation [2]. The relationship between obesity and cardiovascular diseases may be associated with hemody‐ namic and anatomic cardiovascular changes related to excess body mass [30]. However, the relationship can also be mediated by obesity‐related metabolic, inflammatory and neurohor‐ monal changes.

Altered expression of prokineticins and their receptors has been implicated in the development of a number of pathological cardiac conditions, including heart failure [31]. Prokineticins and their receptors have been identified as an important cardiovascular‐signaling system especially cardiac cell commitment and cell‐to‐cell communications [32].

PKR1‐mediated signaling contributes to cardiomyocyte survival and adult heart repair. PKR1 activates Akt in cardiomyocyte to protect these cells against hypoxia‐mediated apoptosis [33]. Transgenic (TG) mice‐overexpressing PKR1 in the cardiomyocytes (TG‐PKR1) had an in‐ creased number of epicardial‐derived progenitor cells (EPDCs), with an increase of capillary density and coronary arterioles. [32] The cardiac‐PKR1 signaling up‐regulates its own ligand prokineticin‐2 to stimulate the EPDC differentiation into endothelial and smooth muscle cells to promote neovasculogenesis [32]. However, cardiomyocyte‐PKR1 is essential for cardio‐ myocyte survival and contractility. PKR1null mice displayed cardiomyocyte‐contractile defects and apoptosis partially due to lack of PKR1 signaling in cardiomyocytes. [34]

In endothelial cells (ECs), PKR1 activates Akt and MAPK to promote proliferation, migration and angiogenesis. In agreement with the *in vitro* findings, the specific loss of PKR1 from mouse ECs resulted in defective angiogenesis, leading to necrosis/apoptosis in the surrounding tissues in several organs, including the heart and kidneys [23].

There was significantly less capillary formation in adult PKR1ec‐/‐ hearts. The posterior walls of PKR1ec‐/‐ hearts were thinner, which was due to the loss of capillary formation and a high level of apoptosis [23]. The remaining viable heart muscle is subject to greater biomechanical stress, triggering hypertrophy [23]. Shortening fractions (indicators of left ventricular contrac‐ tility) were progressively reduced in mutant mice. PKR1ec‐/‐ hearts displayed EC deregulation, capillary refraction, apoptosis, fibrosis and ectopic lipid deposition, abnormal insulin signaling in hearts resulting in impaired diastolic function.

The ECs of hearts exhibited severely decreased FICT‐insulin uptake, indicating defective *transcapillary* transport of insulin in the vascular wall of these mice. Isolated ECs from the mutant cardiac and renal tissues exhibited very little insulin uptake, confirming that the loss of PKR1 from EC decreased insulin transport [23]. Overexpressing PKR1 in these ECs pro‐ moted fluorescein isothiocyanate (FITC)‐insulin passage. Indeed, the primary defect linking insulin resistance and endothelial dysfunction is believed to be nitric oxide deficiency of endothelial origin [35]. In agreement, insulin uptake and insulin‐mediated eNOS activation were impaired in all mutant ECs. Similarly, altered eNOS activation and low insulin action have recently been demonstrated in the endothelium of patients with diabetes mellitus [36]. Thus, impaired insulin delivery to ECs may lead to defective NOS and eNOS activation in PKR1ec‐/‐ aortas, consequently impairing endothelium‐dependent relaxation. These data highlight the role of PKR1 as a positive regulator of insulin uptake [37].

PKR1 signaling also contributes to heart development. In developing heart, PKR1 regulates epicardial‐mesenchymal transition (EMT) to form epicardial‐derived progenitor cell (EPDC) [38]. Genetic ablation of PKR1 in epicardium leads to ventricular hypoplasia and septal defects during embryogenesis. Impaired vasculogenesis in these mice is due to impaired EPDC proliferation as well as a defective EPDC differentiation into endothelial and smooth muscle cell type. PKR1 in EPDCS activates Akt signaling, changes cell morphology, actin cytoskeleton remodeling and EMT gene expression profile. Epicardial‐PKR1 contributes to cardiomyocyte, proliferation and rhythmicity in a paracrine pathway.
