**4. Reproductive system**

The female reproductive system includes, besides external sex organs, the internal sex organs: the ovaries, fallopian tubes, and uterus. Immature at birth, these organs continue to develop and reach maturity at puberty when they can produce gametes, and to carry a fetus to full term. Fallopian tubes integrity is capital for fertilization which usually occurs in the external third of the tubes. The traveling zygote will form the blastocyst that will be implanted in the uterine endometrium. To obtain and maintain a pregnancy, the integrity and functionality of these organs need to be at a maximum.

### **4.1 Telocytes in uterus and fallopian tubes in healthy condition**

Currently, TCs are found in uterine tubes and uterus, including endometrium, myometrium, and cervix, and also in the vagina [2, 3, 62–65]. Among the first

**79**

*Telocytes: New Connecting Devices in the Stromal Space of Organs*

locations in which TCs were described are the organs of the female genital apparatus: the uterus and the fallopian tubes [2, 3, 5, 10, 66]. Since the beginning, their characterization was based on conventional microscopy methods and techniques such as methylene blue staining and silver impregnation, in situ and in vitro [2, 3], followed by the description of the "gold standard" for their identification with the aid of electron microscopy [5]. In parallel, various immunohistochemical markers have been used to enhance TCs better characterization, which has varied over time from vimentin, α-SMA, progesterone receptor, desmin, estrogen receptor, and S100 protein, to stabilize what we consider nowadays to best describe the phenotype of these cells—CD34 and PDGFRα [2, 3, 67]. A book chapter refers to the immunohistochemistry of TCs in female genital organs [28]. However, it should be pointed out that TCs in the uterus and fallopian tubes express receptors for estrogen and progesterone [4, 31]. Nowadays, the most suitable methods for TCs identification are electron microscopy and double staining for CD34 and PDGFRα or PDGFRβ or

In the human uterus, TCs establish homo- and hetero-cellular junctions, demonstrated by electron microscopy images of the telopodes (**Figure 6**) [70]. Homocellular junctions are typically established between two telopodes, but might be observed between a telopode and a TCs' body [71]. The most frequently observed interactions are simple appositions of the plasma membranes; however, puncta adhaerentia minima, processus adhaerens, recessus adhaerens, and manubria adhaerentia can be captured in electron microscopy images [10, 18]. Sometimes, even gap junctions were captured [18]. Hetero-cellular junctions are usually seen between telopodes and fibroblasts, myofibroblasts, pericytes, stem cells, macrophages, mast cells, lymphocytes, plasma cells, Schwann cells, endothelial cell, neurons, cardiomyocytes, and smooth muscle cells, as described in the literature [12, 56, 72–74]. The contacts made between the two membranes are of the type of point contacts, nanocontacts, planar contacts, or simple apposition of plasma

TCs can release exosomes (from multivesicular bodies), ectosomes (shredded directly from plasma membrane), and multivesicular cargos (multiple tightly packed endomembrane-derived vesicles) [75]. The three types of extracellular vesicles emitted by TCs are evidence of the involvement of these cells in intercellular distance communication. Shed vesicle number and diameter are not correlated with the reproductive state, while the quantity of TCs in the endometrium and the myometrium varies with it [17]. Moreover, it was demonstrated that the morphology of telopodes is correlated with the presence or absence of gestation [70]. All these morphological, immunohistochemical, and electrophysiological observations have led to several hypotheses on the TC functions in the uterus and fallopian tubes. The existence of homo-cellular junctions leads to a presumptive function in controlling the shape of the tissues which are subjected to of dynamic changes, such as the pregnant uterus that hypertrophies and expands as the fetus grows [17]. In support of this assumption stands the hypothesis that TCs contribute to smooth muscle growth in areas with high mechanical forces due to TCs mechanical sensitivity [76]. The mechano-sensing function should also be considered, due to the presence of catenins that make up the junctions [18, 71]. Moreover, TCs express T-type calcium (CaV3.1 and CaV3.2) channels and smallconductance calcium-activated potassium channels (SK3) and calcium-dependent hyperpolarization-activated chloride inward channels, the levels of expression being dependent on the physiological state, pregnant or non-pregnant [70, 77, 78]. This point to a TCs' involvement in calcium signaling mechanisms with neighboring cells [79]. Extracellular matrix remodeling is also emphasized by some studies and can be considered as applicable to the uterus [80, 81]. The existence of (ERα)

*DOI: http://dx.doi.org/10.5772/intechopen.89383*

vimentin [68, 69].

membranes [18].

### *Telocytes: New Connecting Devices in the Stromal Space of Organs DOI: http://dx.doi.org/10.5772/intechopen.89383*

*Innovations in Cell Research and Therapy*

**3.2 Telocytes in bladder diseases**

The micturition reflex is the result of a complex integration among involuntary and voluntary nervous mechanisms. Several pathological conditions of the low urinary tract compromise this function causing detrusor dysfunctionality. The most frequent is the idiopathic detrusor overactivity, the neurogenic detrusor overactivity (NDO), the bladder pain syndrome/interstitial cystitis, and the partial bladder outlet obstruction. All these diseases are characterized functionally by excessive sensitivity of the detrusor/bladder to filling [58], and histologically by an intense inflammation especially in the lamina propria [35, 38, 59, 60]. Since it is well known that TCs and myofibroblasts produce cytokines and other molecules able to recruit immune cells and express receptors for the cytokines released by the immune cells, both cell types likely intervene in the inflammation intensity, quality, and duration. Furthermore, in the presence of detrusor hyperactivity, both ULP-TC and myofibroblasts showed an increase of the Cx43 protein labeling that was interpreted as an augmentation of the gap junctions and signs of cellular activation (clear nuclei and larger bodies) [35, 38, 59, 61]. Additionally, the TCs expressing both PDGFRα and α-SMA were significantly increased in comparison with controls suggesting a shift toward a myofibroblast phenotype [35, 38]. All these cell changes were considered signs of adaptability because, despite the presence of inflammation, the 3D cell network was preserved [38, 59]. However, this integrity not necessarily means adequate functionality of the sensory system made by the urothelium and the ULP; in fact, the higher thickness of the ULP, due to the intense cell infiltrate and edema, forcing the net meshes to enlarge, could cause an increase in the distances among the cells, between them and the nerve endings, and between all of them and the urothelium, likely affecting the sensitivity to volume changes and the capability of responding to the molecules released by the nerve terminals and by the urothelium. Finally, because the ULP thickening was uneven alongside the organ [35, 38, 60], foci of hypersensitivity could alternate to others less responding, further prejudicing the correct integration of the afferent stimuli [57]. Finally, it was reported that the TCs forming the monolayer underlying the urothelium did not show any significant changes in hyperactive bladders. These data were explained as follow: the location of these TCs could spare them from the damages caused by the cell infiltrate. Further, if these TCs are engaged in cell proliferation and differentiation of the overlying epithelium, the absence of epithelial cell death signs in NDO might

The female reproductive system includes, besides external sex organs, the internal sex organs: the ovaries, fallopian tubes, and uterus. Immature at birth, these organs continue to develop and reach maturity at puberty when they can produce gametes, and to carry a fetus to full term. Fallopian tubes integrity is capital for fertilization which usually occurs in the external third of the tubes. The traveling zygote will form the blastocyst that will be implanted in the uterine endometrium. To obtain and maintain a pregnancy, the integrity and functionality of these organs

Currently, TCs are found in uterine tubes and uterus, including endometrium, myometrium, and cervix, and also in the vagina [2, 3, 62–65]. Among the first

**4.1 Telocytes in uterus and fallopian tubes in healthy condition**

**78**

account for their sparing.

**4. Reproductive system**

need to be at a maximum.

locations in which TCs were described are the organs of the female genital apparatus: the uterus and the fallopian tubes [2, 3, 5, 10, 66]. Since the beginning, their characterization was based on conventional microscopy methods and techniques such as methylene blue staining and silver impregnation, in situ and in vitro [2, 3], followed by the description of the "gold standard" for their identification with the aid of electron microscopy [5]. In parallel, various immunohistochemical markers have been used to enhance TCs better characterization, which has varied over time from vimentin, α-SMA, progesterone receptor, desmin, estrogen receptor, and S100 protein, to stabilize what we consider nowadays to best describe the phenotype of these cells—CD34 and PDGFRα [2, 3, 67]. A book chapter refers to the immunohistochemistry of TCs in female genital organs [28]. However, it should be pointed out that TCs in the uterus and fallopian tubes express receptors for estrogen and progesterone [4, 31]. Nowadays, the most suitable methods for TCs identification are electron microscopy and double staining for CD34 and PDGFRα or PDGFRβ or vimentin [68, 69].

In the human uterus, TCs establish homo- and hetero-cellular junctions, demonstrated by electron microscopy images of the telopodes (**Figure 6**) [70]. Homocellular junctions are typically established between two telopodes, but might be observed between a telopode and a TCs' body [71]. The most frequently observed interactions are simple appositions of the plasma membranes; however, puncta adhaerentia minima, processus adhaerens, recessus adhaerens, and manubria adhaerentia can be captured in electron microscopy images [10, 18]. Sometimes, even gap junctions were captured [18]. Hetero-cellular junctions are usually seen between telopodes and fibroblasts, myofibroblasts, pericytes, stem cells, macrophages, mast cells, lymphocytes, plasma cells, Schwann cells, endothelial cell, neurons, cardiomyocytes, and smooth muscle cells, as described in the literature [12, 56, 72–74]. The contacts made between the two membranes are of the type of point contacts, nanocontacts, planar contacts, or simple apposition of plasma membranes [18].

TCs can release exosomes (from multivesicular bodies), ectosomes (shredded directly from plasma membrane), and multivesicular cargos (multiple tightly packed endomembrane-derived vesicles) [75]. The three types of extracellular vesicles emitted by TCs are evidence of the involvement of these cells in intercellular distance communication. Shed vesicle number and diameter are not correlated with the reproductive state, while the quantity of TCs in the endometrium and the myometrium varies with it [17]. Moreover, it was demonstrated that the morphology of telopodes is correlated with the presence or absence of gestation [70].

All these morphological, immunohistochemical, and electrophysiological observations have led to several hypotheses on the TC functions in the uterus and fallopian tubes. The existence of homo-cellular junctions leads to a presumptive function in controlling the shape of the tissues which are subjected to of dynamic changes, such as the pregnant uterus that hypertrophies and expands as the fetus grows [17]. In support of this assumption stands the hypothesis that TCs contribute to smooth muscle growth in areas with high mechanical forces due to TCs mechanical sensitivity [76]. The mechano-sensing function should also be considered, due to the presence of catenins that make up the junctions [18, 71]. Moreover, TCs express T-type calcium (CaV3.1 and CaV3.2) channels and smallconductance calcium-activated potassium channels (SK3) and calcium-dependent hyperpolarization-activated chloride inward channels, the levels of expression being dependent on the physiological state, pregnant or non-pregnant [70, 77, 78]. This point to a TCs' involvement in calcium signaling mechanisms with neighboring cells [79]. Extracellular matrix remodeling is also emphasized by some studies and can be considered as applicable to the uterus [80, 81]. The existence of (ERα)

### **Figure 6.**

*Representative ultrathin section of human pregnant myometrium. Two-dimensional sequenced concatenation from 11 serial electron micrographs showing the 3D network of TCs (blue) interconnected by homo-cellular junctions (dotted circles). SMCs are shown in cross-section and were digitally colored brown. In their vicinity, numerous Tps (blue) establish a network and release extracellular organelles (exosomes and shedding vesicles [arrowheads]) digitally colored purple. One mast cell (green) is in the vicinity of this network. Some vesicles were captured at the moment of being shed from Tps (\*). Cav = caveolae; coll = collagen; m = mitochondria; rER = rough endoplasmic reticulum; N¼nucleus. Bar¼2 lm. Reproduced with permission from Ref. [10].*

and progesterone receptor A (PR-A) on the surface of uterine TCs suggests their involvement as sensors for steroid hormones levels. Although little is known about the existence of stem cells in the uterus, they certainly exist, and the secretome of the TCs could influence the cellular microenvironment, controlling their proliferation, and differentiation [15]. Also, TCs secretome factors could participate in decidua formation [17]. Some studies pointed to the angiogenic properties of TCs

**81**

*Telocytes: New Connecting Devices in the Stromal Space of Organs*

due to vascular endothelial growth factor (VEGF) expression [15, 82, 83], while others indicated the anti-oxidative properties of TCs because the TCs specific morphology can be changed by modifying the redox balance of their environment or by aging due to their richness in SOD2 (mitochondrial superoxide dismutase) [21, 84]. Recently, TCs were found to activate and "educate" peritoneal macrophages (pMACs) with the aid of telopodes by direct physical contact through heterocellular junctions or using a TCs-conditioned media through paracrine mecha-

In the fallopian tubes, TCs have been described throughout the thickness of the wall, their density decreasing from the mucosa to the muscular, from ∼18 to ∼7.5% [3]. TCs are also found in the fimbriae of Fallopian tubes [17, 28]. A panel of antibodies was used to identify tubal TCs. The telopodes possess all the features described above, creating a 3D network and establishing contacts with different structures, such as blood vessels, nerves, and muscle fibers [86, 87]. Both, homoand hetero-cellular junctions are described, and also, a new hypothesis was emitted that telopodes that contact the immune cells (plasma cells and lymphocytes) might stimulate antibody production [88, 89]. As suggested by Cretoiu et al., the tubal peristalsis might suffer influences from TCs which also express PR-A and ERα receptors [31]. The tubal movements seem to be amplified by estrogen and decelerated by progesterone [90]. Recently, additional markers were tested for TCs identification, such as Podoplanin (D2–40) and Dog-1 but proved to be

The pathogenesis of uterine leiomyomas, the most frequent benign tumors in women might be determined, among other factors, by the loss of TCs [26]. Varga et al. proposed three hypotheses regarding TCs' involvement: (i) loss of TCs as steroid sensors leads to an increased density of estrogen receptors at smooth muscle cells level followed by a cell cycle disruption; (ii) considered as progenitor cells, TCs absence can favor the rise of new leiomyoma cells; and (iii) in the absence of antioxidant protection conferred by TCs, leiomyoma cells grow numerically due to

A recent study shows, for the first time, that there is an interplay between telocytes and autonomic innervation in leiomyomata [92]. TCs decreased in numbers in the leiomyomatous myometrium, suggesting a role for these cells in the control

the overproduction of iNOS, COX-2, LPO, and estradiol [49, 69, 88].

gamete maturation, fertilization, and early embryo development [100].

Some other pathologies that might affect the 3-D network of TCs were described, such as Chlamydia infection responsible for the activation of macrophages or pelvic inflammatory disease [89, 98, 99]. In inflammation and ischemia, TCs were shown to be lost and to suffer major ultrastructural changes, a process followed by interstitial fibrotic remodeling [99]. Abd-Elhafeez et al. proposed a role for tubal TCs in the regulation of the epithelial function necessary for the final

The integrity of the 3D network of TCs appears to be fundamental in exercising the function of the fallopian tubes that are regarded as a major organ in the reproduction. Several studies showed that by affecting the 3D organization and number of TCs perturbations occur in the local homeostasis, leading to angiogenesis and interstitial fibrosis [88, 89]. Neo-angiogenesis plays a major role in endometriosis and adenomyosis pathogenesis, and even in tubal ectopic pregnancy [93–95]. TCs were shown to be involved in all these processes [96, 97]. In pelvic endometriosis and tubal ectopic pregnancy, the decrease in the number of TCs is probably due to

nisms [85]. This is suggestive for a role in immunosurveillance [85].

*DOI: http://dx.doi.org/10.5772/intechopen.89383*

inappropriate [91].

**4.2 Telocytes in uterine and tubal diseases**

local hypoxia that blocks their apoptosis [26].

of the microenvironment [92].

*Telocytes: New Connecting Devices in the Stromal Space of Organs DOI: http://dx.doi.org/10.5772/intechopen.89383*

*Innovations in Cell Research and Therapy*

**80**

**Figure 6.**

and progesterone receptor A (PR-A) on the surface of uterine TCs suggests their involvement as sensors for steroid hormones levels. Although little is known about the existence of stem cells in the uterus, they certainly exist, and the secretome of the TCs could influence the cellular microenvironment, controlling their proliferation, and differentiation [15]. Also, TCs secretome factors could participate in decidua formation [17]. Some studies pointed to the angiogenic properties of TCs

*Representative ultrathin section of human pregnant myometrium. Two-dimensional sequenced concatenation from 11 serial electron micrographs showing the 3D network of TCs (blue) interconnected by homo-cellular junctions (dotted circles). SMCs are shown in cross-section and were digitally colored brown. In their vicinity, numerous Tps (blue) establish a network and release extracellular organelles (exosomes and shedding vesicles [arrowheads]) digitally colored purple. One mast cell (green) is in the vicinity of this network. Some vesicles were captured at the moment of being shed from Tps (\*). Cav = caveolae; coll = collagen; m = mitochondria; rER = rough endoplasmic reticulum; N¼nucleus. Bar¼2 lm. Reproduced with permission from Ref. [10].*

due to vascular endothelial growth factor (VEGF) expression [15, 82, 83], while others indicated the anti-oxidative properties of TCs because the TCs specific morphology can be changed by modifying the redox balance of their environment or by aging due to their richness in SOD2 (mitochondrial superoxide dismutase) [21, 84].

Recently, TCs were found to activate and "educate" peritoneal macrophages (pMACs) with the aid of telopodes by direct physical contact through heterocellular junctions or using a TCs-conditioned media through paracrine mechanisms [85]. This is suggestive for a role in immunosurveillance [85].

In the fallopian tubes, TCs have been described throughout the thickness of the wall, their density decreasing from the mucosa to the muscular, from ∼18 to ∼7.5% [3]. TCs are also found in the fimbriae of Fallopian tubes [17, 28]. A panel of antibodies was used to identify tubal TCs. The telopodes possess all the features described above, creating a 3D network and establishing contacts with different structures, such as blood vessels, nerves, and muscle fibers [86, 87]. Both, homoand hetero-cellular junctions are described, and also, a new hypothesis was emitted that telopodes that contact the immune cells (plasma cells and lymphocytes) might stimulate antibody production [88, 89]. As suggested by Cretoiu et al., the tubal peristalsis might suffer influences from TCs which also express PR-A and ERα receptors [31]. The tubal movements seem to be amplified by estrogen and decelerated by progesterone [90]. Recently, additional markers were tested for TCs identification, such as Podoplanin (D2–40) and Dog-1 but proved to be inappropriate [91].

### **4.2 Telocytes in uterine and tubal diseases**

The pathogenesis of uterine leiomyomas, the most frequent benign tumors in women might be determined, among other factors, by the loss of TCs [26]. Varga et al. proposed three hypotheses regarding TCs' involvement: (i) loss of TCs as steroid sensors leads to an increased density of estrogen receptors at smooth muscle cells level followed by a cell cycle disruption; (ii) considered as progenitor cells, TCs absence can favor the rise of new leiomyoma cells; and (iii) in the absence of antioxidant protection conferred by TCs, leiomyoma cells grow numerically due to local hypoxia that blocks their apoptosis [26].

A recent study shows, for the first time, that there is an interplay between telocytes and autonomic innervation in leiomyomata [92]. TCs decreased in numbers in the leiomyomatous myometrium, suggesting a role for these cells in the control of the microenvironment [92].

The integrity of the 3D network of TCs appears to be fundamental in exercising the function of the fallopian tubes that are regarded as a major organ in the reproduction. Several studies showed that by affecting the 3D organization and number of TCs perturbations occur in the local homeostasis, leading to angiogenesis and interstitial fibrosis [88, 89]. Neo-angiogenesis plays a major role in endometriosis and adenomyosis pathogenesis, and even in tubal ectopic pregnancy [93–95]. TCs were shown to be involved in all these processes [96, 97]. In pelvic endometriosis and tubal ectopic pregnancy, the decrease in the number of TCs is probably due to the overproduction of iNOS, COX-2, LPO, and estradiol [49, 69, 88].

Some other pathologies that might affect the 3-D network of TCs were described, such as Chlamydia infection responsible for the activation of macrophages or pelvic inflammatory disease [89, 98, 99]. In inflammation and ischemia, TCs were shown to be lost and to suffer major ultrastructural changes, a process followed by interstitial fibrotic remodeling [99]. Abd-Elhafeez et al. proposed a role for tubal TCs in the regulation of the epithelial function necessary for the final gamete maturation, fertilization, and early embryo development [100].
