Growth hormone action in the developing neural retina: A proteomic analysis

Corneal parameters, ocular biometers, and retinal and choroidal thickness in acromegaly patients

BACKGROUND

To compare ocular findings of acromegaly patients with healthy individuals and investigate the relation of serum levels of insulin-like growth factor (IGF-1) along with growth hormone (GH) and pituitary tumor (adenoma) dimensions (TD) with specific ocular parameters.

METHODS

The ocular parameters of acromegaly patients (n = 38) were compared with those of healthy subjects (n = 36). These parameters were intraocular pressure, keratometric (K1-K2) values, central corneal thickness (CCT), total axial length along with anterior chamber-lens-vitreous length, retinal nerve fiber layer (RNFL) thickness, central foveal thickness (CFT), choroidal thickness (CT), ganglion cell layer thickness (GCLT), and inner plexiform layer thickness (IPLT). Also investigated was whether there was a correlation between disease duration, TD, GH, IGF-I, CCT, RNFL, CFT, GCLT, IPLT, and CT.

RESULTS

The lens length of the acromegaly group was increased (p = 0.014). GH and IGF-1 levels were positively correlated with CT and CCT, respectively (p = 0.041, r = 0.343) (p = 0.03, r = 0.347). Analysis of TD also found a highly negative correlation with the mean RNFL thickness of the acromegaly patients (p < 0.01, r = -0.603). The mean value of the inner parts of GCLT and IPLT was negatively correlated with TD (p = 0.041, r = -0.343 and p = 0.025, r = -0.379, respectively).

CONCLUSION

Serum IGF-1 and GH levels might be determinant factors in CCT and CT, respectively. The pituitary adenoma size increasing may be prone to lead RNFL, ganglion cell layer, inner plexiform layer thinning. Increased lens thickness was found in the acromegaly group.

The Effects of Long-term Growth Hormone Treatment on Ocular Findings

PURPOSE

This study aimed to examine the long-term changes in anterior chamber depth (ACD), central corneal thickness (CCT), axial length (AxL), peripapillary retinal nerve fibre layer thickness (RNFLT), peripapillary ganglion cell layer - inner plexiform layer (GCL-IPL) thickness, and peripapillary choroidal thickness (ChT) after rhGH replacement treatment in paediatric patients with IGHD, compared to healthy controls.

METHODS

Twenty-two children with IGHD including 12 girls and 10 boys were enrolled in the study group, and 30 (16 girls, 14 boys) healthy children composed the control group. A detailed ophthalmological examination was performed for each participant. ACD, CCT, AxL, peripapillary RNFLT, GCL-IPL thickness and ChT measurements were performed before the rhGH replacement treatment and in the 12th month of the post-treatment period, as well as the corresponding visits in the control group. AxL ultrasound pachymetry (CCT), peripapillary RNFL thickness, peripapillary RNFLT, GCL-IPL thickness, and peripapillary ChT parameters were measured by spectral-domain optical coherence tomography.

RESULTS

The mean age of the groups were similar (p = 0.143). 12-month CCT, ACD, and AxL measurements of the study group showed significantly higher results than the pre-treatment measurements (p = 0.005, p = 0.024, and p = 0.002, respectively). Similarly, the mean RNFLT and ChT measurements of the study group obtained from all sectors were significantly higher in the 12th-month visit (p < 0.001 for both) other than the RNFLT, and GCL-IPL thickness measurements (p > 0.05 for all). However, all these parameters were similar at pre- and post-treatment visits in the control group (p > 0.05 for all). The mean pre-treatment values of all these parameters were significantly lower in the study group compared to the control group (p < 0.05 for all), other than the RNFLT, GCL-IPL thickness measurements (p > 0.05 for all), while the mean post-treatment values of all these parameters in both groups were similar at month 12 (p > 0.05 for all).

CONCLUSION

GH replacement treatment in childhood may play an important role in the development of the neural retina and can be effective on the anterior segment, RNFLT and ChT measurements.

Growth hormone (GH) and synaptogenesis

Growth hormone (GH) is known to exert several roles during development and function of the nervous system. Initially, GH was exclusively considered a pituitary hormone that regulates body growth and metabolism, but now its alternative extrapituitary production and pleiotropic functions are widely accepted. Through excess and deficit models, the critical role of GH in nervous system development and adult brain function has been extensively demonstrated. Moreover, neurotrophic actions of GH in neural tissues include pro-survival effects, neuroprotection, axonal growth, synaptogenesis, neurogenesis and neuroregeneration. The positive effects of GH upon memory, behavior, mood, sensorimotor function and quality of life, clearly implicate a beneficial action in synaptic physiology. Experimental and clinical evidence about GH actions in synaptic function modulation, protection and restoration are revised in this chapter.

Retinal Neural and Vascular Structure in Isolated Growth Hormone Deficiency Children and Evaluation of Growth Hormone Treatment Effect

OBJECTIVE

To evaluate neural and vascular retinal morphology of children with isolated growth hormone deficiency (GHD) and to determine any retinal changes due to GH treatment.

METHODS

Twenty-eight children with isolated GHD and 53 age-, gender- and body mass index-matched healthy volunteers were enrolled in this prospective study. The retinal nerve fibre layer (RNFL) and macular thickness (MT) were measured, as well as intraocular pressure (IOP). The number of retinal vascular branching points were calculated. Effect of GH treatment on the retina and IOP was evaluated after one year of treatment. Measurements were also made in the control group at baseline and following the initial examination. Pre- and post-treatment changes were compared. The findings were also compared with those of the controls. The correlation between ocular dimensions and insulin-like growth factor-I (IGF-1) levels were also analysed.

RESULTS

The number of branching points was significantly lower in GHD patients as compared with control subjects (15.11±2.67 and 19.70±3.37, respectively, p=0.05 for all comparisons). No statistically significant differences were found in mean RNFL, MT and IOP values between GHD patients and control subjects. GH treatment did not create any significant changes in the retinal vascularization or other retinal neural parameters and IOP either within the patient group or when compared with the control group. No correlations were observed between ocular dimensions and IGF-1 levels.

CONCLUSION

Our findings suggest that isolated GHD may lead to decreased retinal vascularization. However, retinal neural growth and differentiation were not affected by GHD. These findings may be related to the fetal development process of pituitary somatotropic cells and the retina. Additionally, GH treatment did not cause any changes in retinal neural and vascular tissues.

Choroidal thickness measurements in children with isolated growth hormone deficiency

PurposeThe aim of this study was to determine the choroidal thickness measurement values in cases with isolated growth hormone deficiency (IGHD), to compare them with the healthy control group by using enhanced depth imaging optical coherence tomography (EDI-OCT), and to evaluate the effect of growth hormone (GH) treatment on choroid.Patients and methodsIn this study, 23 cases who were diagnosed with IGHD as a study group and 46 healthy subjects as a control group were included. All patients and controls underwent a complete ophthalmologic examination, including an examination with EDI-OCT. Choroidal thickness (CT) was measured at the fovea and at 1000 μm intervals from the foveal center in both temporal and nasal directions.ResultsThe mean subfoveal choroidal thickness (SFCT) was 329.04±88.49 μm in the cases with IGHD and 365.35±50.48 μm in the control group (P=0.033). The mean CT at temporal 1 and 2 mm were thinner in the IGHD group than that of control group (P=0.033 and P=0.043, respectively). Nasal quadrant measurements were also found to be thinner in the IGHD cases than that of control group, but the difference was not statistically significant. We found a significant positive correlation between pubertal staging and SFCT (r_s=0.607, P=0.006). There was no statistically significant difference in CT values of the study group between before and 12 months after GH treatment (P>0.05).ConclusionThis study shows patients with IGHD has a thinner CT when compared with healthy pediatric cases. GH treatment seems to be not associated with the choroidal development.

Ocular findings in adult subjects with an inactivating mutation in GH releasing hormone receptor gene

OBJECTIVE

Ocular function is fundamental for environmental adaptation and survival capacity. Growth factors are necessary for a mature eyeball, needed for adequate vision. However, the consequences of the deficiency of circulating growth hormone (GH) and its effector insulin-like growth factor I (IGF-I) on the physical aspects of the human eye are still debated. A model of untreated isolated GH deficiency (IGHD), with low but measurable serum GH, may clarify this issue. The aim of this study was to assess the ocular aspects of adult IGHD individuals who have never received GH therapy.

DESIGN

Cross sectional study.

METHODS

Setting: University Hospital, Federal University of Sergipe, Brazil.

PATIENTS

Twenty-five adult (13 males, mean age 50.1years, range 26 to 70years old) IGHD subjects homozygous for a null mutation (c.57+1G>A) in the GHRH receptor gene, and 28 (15 males, mean age 51.1years, range 26 to 67years old) controls were submitted to an endocrine and ophthalmological assessment. Forty-six IGHD and 50 control eyes were studied.

MAIN OUTCOME MEASURES

Visual acuity, intraocular pressure, refraction (spherical equivalent), ocular axial length (AL), anterior chamber depth (ACD), lens thickness (LT), vitreous depth (VD), mean corneal curvature (CC) and central corneal thickness (CCT).

RESULTS

IGHD subjects exhibited unmeasurable serum IGF-I levels, similar visual acuity, intraocular pressure and LT, higher values of spherical equivalent and CC, and lower measures of AL, ACD, VD and CCT in comparison to controls, but within their respective normal ranges. While mean stature in IGHD group was 78% of the control group, mean head circumference was 92% and axial AL was 96%.

CONCLUSIONS

These observations suggest mild ocular effects in adult subjects with severe IGF-I deficiency due to non-treated IGHD.

Abnormal vascular and neural retinal morphology in congenital lifetime isolated growth hormone deficiency

OBJECTIVE

Experimental models demonstrate an important role of GH in retinal development. However, the interactions between GH and the neuro-vascularization of the human retina are still not clear. A model of untreated congenital isolated GH deficiency (IGHD) may clarify the actions of GH on the retina. The purpose of this work was to assess the retinal neuro-vascularization in untreated congenital IGHD (cIGHD).

DESIGN

In a cross sectional study, we performed an endocrine and ophthalmological assessment of 25 adult cIGHD subjects, homozygous for a null mutation (c.57+1G>A) in the GHRH receptor gene and 28 matched controls. Intraocular pressure measurement, retinography (to assess the number of retinal vascular branching points and the optic disc and cup size), and optical coherence tomography (to assess the thickness of macula) were performed.

RESULTS

cIGHD subjects presented a more significant reduction of vascular branching points in comparison to controls (91% vs. 53% [p=0.049]). The percentage of moderate reduction was higher in cIGHD than in controls (p=0.01). The percentage of individuals with increased optic disc was higher in cIGHD subjects in comparison to controls (92.9% vs. 57.1%). The same occurred for cup size (92.9% vs. 66.7%), p<0.0001 in both cases. There was no difference in macula thickness.

CONCLUSIONS

Most cIGHD individuals present moderate reduction of vascular branching points, increase of optic disc and cup size, but have similar thickness of the macula.

Growth hormone and ocular dysfunction: Endocrine, paracrine or autocrine etiologies?

The eye is a target site for GH action and growth hormone has been implicated in diabetic retinopathy and other ocular dysfunctions. However, while this could reflect the hypersecretion of pituitary GH, the expression of the GH gene is now known to occur in ocular tissues and it could thus also reflect excess GH production within the eye itself. The possibility that ocular dysfunctions might arise from endocrine, autocrine or paracrine etiologies of GH overexpression is therefore the focus of this brief review.

Internalization and synaptogenic effect of GH in retinal ganglion cells (RGCs)

In the chicken embryo, GH gene expression occurs in the neural retina and retinal GH promotes cell survival and induces axonal growth of retinal ganglion cells. Neuroretinal GH is therefore of functional importance before the appearance of somatotrophs and the onset of pituitary GH secretion to the peripheral plasma (at ED15-17). Endocrine actions of pituitary GH in the development and function of the chicken embryo eye are, however, unknown. This possibility has therefore been investigated in ED15 embryos and using the quail neuroretinal derived cell line (QNR/D). During this research, we studied for the first time, the coexistence of exogenous (endocrine) and local GH (autocrine/paracrine) in retinal ganglion cells (RGCs). In ovo systemic injections of Cy3-labeled GH demonstrated that GH in the embryo bloodstream was translocated into the neural retina and internalized into RGC's. Pituitary GH may therefore be functionally involved in retinal development during late embryogenesis. Cy3-labelled GH was similarly internalized into QNR/D cells after its addition into incubation media. The uptake of exogenous GH was by a receptor-mediated mechanism and maximal after 30-60min. The exogenous (endocrine) GH induced STAT5 phosphorylation and increased growth associated protein 43 (GAP43) and SNAP-25 immunoreactivity. Ex ovo intravitreal injections of Cy3-GH in ED12 embryos resulted in GH internalization and STAT5 activation. Interestingly, the CY3-labeled GH accumulated in perinuclear regions of the QNR/D cells, but was not found in the cytoplasm of neurite outgrowths, in which endogenous retinal GH is located. This suggests that exogenous (endocrine) and local (autocrine/paracrine) GH are both involved in retinal function in late embryogenesis but they co-exist in separate intracellular compartments within retinal ganglion cells.

Growth hormone in the eye: A comparative update

Comparative studies have previously established that the eye is an extrapituitary site of growth hormone (GH) production and action in fish, amphibia, birds and mammals. In this review more recent literature and original data in this field are considered.

Genomic structure and marker-derived gene networks for growth and meat quality traits of Brazilian Nelore beef cattle

BACKGROUND

Nelore is the major beef cattle breed in Brazil with more than 130 million heads. Genome-wide association studies (GWAS) are often used to associate markers and genomic regions to growth and meat quality traits that can be used to assist selection programs. An alternative methodology to traditional GWAS that involves the construction of gene network interactions, derived from results of several GWAS is the AWM (Association Weight Matrices)/PCIT (Partial Correlation and Information Theory). With the aim of evaluating the genetic architecture of Brazilian Nelore cattle, we used high-density SNP genotyping data (~770,000 SNP) from 780 Nelore animals comprising 34 half-sibling families derived from highly disseminated and unrelated sires from across Brazil. The AWM/PCIT methodology was employed to evaluate the genes that participate in a series of eight phenotypes related to growth and meat quality obtained from this Nelore sample.

RESULTS

Our results indicate a lack of structuring between the individuals studied since principal component analyses were not able to differentiate families by its sires or by its ancestral lineages. The application of the AWM/PCIT methodology revealed a trio of transcription factors (comprising VDR, LHX9 and ZEB1) which in combination connected 66 genes through 359 edges and whose biological functions were inspected, some revealing to participate in biological growth processes in literature searches.

CONCLUSIONS

The diversity of the Nelore sample studied is not high enough to differentiate among families neither by sires nor by using the available ancestral lineage information. The gene networks constructed from the AWM/PCIT methodology were a useful alternative in characterizing genes and gene networks that were allegedly influential in growth and meat quality traits in Nelore cattle.

Comparing acromegalic patients to healthy controls with respect to intraocular pressure, central corneal thickness, and optic disc topography findings

Aims:

The aim was to compare the intraocular pressure (IOP), central corneal thickness (CCT), and optic disc topography findings of biochemically controlled acromegalic patients and the control group and to evaluate the effect of the duration of acromegaly and serum growth hormone and insulin-like growth factor-1 (IGF-1) levels on these ocular parameters.

Materials and Methods:

IOP measurement with Goldmann applanation tonometry, CCT measurement with ultrasonic pachymetry, and topographic analysis with Heidelberg retinal tomograph III were performed on 35 biochemically controlled acromegalic patients and 36 age- and gender-matched controls.

Results:

Mean IOP and CCT were 14.7 ± 2.9 mmHg and 559.5 ± 44.9 μm in the acromegaly patients and 13.0 ± 1.6 mmHg and 547.1 ± 26.7 μm in controls (P = 0.006 and P = 0.15, respectively). A significant moderate correlation was found between the duration of acromegaly and CCT (r = 0.391) and IOP (r = 0.367). Mean retinal nerve fiber layer (RNFL) thickness was significantly lower in the acromegalic patients (0.25 ± 0.05 mm) as compared to controls (0.31 ± 0.09 mm) (P = 0.01). A significant moderate correlation was detected between IGF-1 level and disc area (r = 0.362), cup area (r = 0.389) and cup volume (r = 0.491).

Conclusion:

Biochemically controlled acromegalic patients showed significantly higher CCT and IOP levels and lower RNFL thickness compared to healthy controls and the duration of disease was correlated with CCT and IOP levels.

Corneal thickness in children with growth hormone deficiency: the effect of GH treatment

OBJECTIVE

The eye represents a target site for GH action, although few data are available in patients with GH deficiency (GHD). Our aim was to evaluate central corneal thickness (CCT) and intraocular pressure (IOP) values in GHD children to assess the role played by GHD or GH treatment on these parameters.

DESIGN

In 74 prepubertal GHD children (51M, 23F, aged 10.4±2.4years) we measured CCT and IOP before and after 12months of treatment. A baseline evaluation was also made in 50 healthy children matched for age, gender and body mass index. The study outcome considered CCT and IOP during treatment and their correlations with biochemical and auxological data.

RESULTS

No difference in CCT and IOP between GHD children at baseline and controls was found (all p>0.005). GHD children after 12months of therapy showed greater CCT (564.7±13.1μm) than both baseline values (535.7±17μm; p<0.001) and control subjects (536.2±12.5μm; p<0.001), with a concomitantly higher corrected mean IOP (15.6±0.7mmHg; p<0.001) than both baseline (12.5±0.8mmHg; p<0.001) and controls (12.3±0.5mmHg; p<0.001), without correlation with auxological and biochemical parameters.

CONCLUSIONS

12months of GH treatment in children with GHD, regardless of auxological and biochemical data, affect CCT and IOP. Our findings suggest careful ocular evaluation in these patients to prevent undesirable side effects during the follow-up.

Decreased Retinal Nerve Fiber Layer Thickness in Patients with Congenital Isolated Growth Hormone Deficiency

Purpose

To evaluate the optic disc topography parameters of children with congenital isolated growth hormone deficiency (GHD) using the Heidelberg retina tomograph (HRT) in a controlled study.

Methods

This prospective study included 32 eyes of 32 patients with congenital isolated GHD and 36 eyes of 36 healthy subjects. The topographic optic disc parameters (mean cup volume, rim volume, cup area, disc area, rim area, mean cup-to-disc ratio and cup depth, retinal nerve fiber layer thickness [RNFL]) were imaged in all subjects with HRT-III (software 3.01 a-M). Pearson correlation analysis was used to investigate the correlation between right and left eyes regarding the optic disc parameters. Differences between the 2 groups were evaluated by independent t test, Mann-Whitney U test, and chi-square test.

Results

The mean RNFL thickness in children with congenital isolated GHD was found to be statistically significantly thinner than in healthy subjects (p<0.05). However, no statistically significant differences were found between the mean cup volume, rim volume, cup area, disc area, rim area, mean cup-to-disc ratio and cup depth, and mean sectorial RNFL thickness (p>0.05).

Conclusions

The results suggest that congenital GHD may lead to thinner RNFL thickness when compared with healthy subjects. This indicates that GH has an important role in the development of the neural retina.

Age- and sex-associated plasma proteomic changes in growth hormone receptor gene-disrupted mice

Growth hormone receptor gene-disrupted (GHR-/-) mice are dwarf, insulin sensitive, and long lived despite being obese. In order to identify characteristics associated with their increased longevity, we studied age-related plasma proteomic changes in these mice. Male and female GHR-/- mice and their littermate controls were followed longitudinally at 8, 16, and 24 months of ages for plasma proteomic analysis. Relative to control littermates, GHR-/- mice had increased levels of apolipoprotein A-4 and retinol-binding protein-4 and decreased levels of apolipoprotein E, haptoglobin, and mannose-binding protein-C. Female GHR-/- mice showed decreased inflammatory cytokines including interleukin-1β and monocyte chemotactic protein-1. Additionally, sex differences were found in specific isoforms of apolipoprotein E, RBP-4, haptoglobin, albumin, and hemoglobin subunit beta. In conclusion, we find plasma proteomic changes in GHR-/- mice that favor a longer life span as well as sex differences indicative of an improved health span in female mice.

Selective inner retinal dysfunction in growth hormone transgenic mice

OBJECTIVE

The discovery of locally produced growth hormone (GH) and its receptor in the retina of rodents raises the possibility that GH might modulate retinal function. To test this hypothesis, we determined the retinal electroretinogram (ERG) of bovine GH (bGH) transgenic mice.

DESIGN

ERGs were recorded from 11 wild type (WT) and 9 bGH mice, at 2 months of age in response to a series of light flashes at increasing intensity. Three ERG components were assessed for their amplitude and timing: a-wave, b-wave and oscillatory potentials (OPs). OPs were isolated with a 75-300 Hz digital filter. Retina layer sizes, nuclei number and vascularization were assessed by respectively staining cross sections with DAPI and Bandeiraea simplicifolia.

RESULTS

OPs were selectively affected in the bGH mouse compared to WT. When OP amplitude values were normalized to the a-wave amplitude (to account for inter-animal variability in WT and bGH groups), OP2, OP3, and OP4 showed amplitude reductions (of 65%, 72%, and 68%, respectively) in the bGH mouse compared to the WT. This was accompanied by a prolongation of the implicit time for the peak of OP3 (28.1 vs 31.1 ms, WT vs bGH) and OP4 (37.8 vs 41.6 ms), while the implicit time of a- and b-waves were unaffected. Fast Fourier transform analysis revealed that the OPs' dominant frequency was significantly reduced (P<0.05) in the bGH mice (100 Hz) compared to WT (108Hz). There was no significant change in retinal histology except for a significant increase in the axial length of the eye in bGH mice.

CONCLUSIONS

Mice expressing bGH display a selective inner retinal defect as demonstrated using ERG recordings. The specific OP defect observed in these mice is similar to the ERG results obtained in patients with diabetic retinopathy and in related animal models.

Cornea in acromegalic patients as a possible target of growth hormone action

BACKGROUND

GH exerts its effects on many organs and the eye also seems to be a target site, although few authors have investigated the corneal thickness in patients with acromegaly.

AIM

To perform a detailed ophthalmological evaluation in acromegalic patients, in relation to disease activity.

MATERIAL AND METHODS

Twenty-eight acromegalic patients (11 males, 17 females) and 22 voluntary healthy subjects underwent complete metabolic and ophthalmological evaluation, including retinal thickness (RT), central corneal thickness (CCT), and intraocular pressure values (IOP).

RESULTS

Significantly greater CCT values were found in all acromegalic patients in comparison with controls (567 vs 528.5 μm; p<0.001), without concomitant greater corrected IOP. No difference was found for RT. Analyzing these data according to disease activity, uncontrolled patients showed greater CCT values (573.5 vs 559 μm; p=0.002) and corrected IOP (17.4 vs 16 mmHg; p=0.001) than the controlled ones. CCT also correlated with basal and nadir GH after oral glucose load levels, IGF-I levels, and duration of active disease.

CONCLUSIONS

Acromegaly is characterized by greater CCT values, supporting the hypothesis that GH excess may have stimulatory effects on the cornea as well as on other target organs. Higher GH levels, disease control status and duration of active disease seem to be the main causes of increased corneal thickness. We suggest a careful and detailed corneal evaluation in acromegalic patients to prevent the potential risk of increased IOP, in addition to the already-known complications.

Extrapituitary growth hormone

Pituitary somatotrophs secrete growth hormone (GH) into the bloodstream, to act as a hormone at receptor sites in most, if not all, tissues. These endocrine actions of circulating GH are abolished after pituitary ablation or hypophysectomy, indicating its pituitary source. GH gene expression is, however, not confined to the pituitary gland, as it occurs in neural, immune, reproductive, alimentary, and respiratory tissues and in the integumentary, muscular, skeletal, and cardiovascular systems, in which GH may act locally rather than as an endocrine. These actions are likely to be involved in the proliferation and differentiation of cells and tissues prior to the ontogeny of the pituitary gland. They are also likely to complement the endocrine actions of GH and are likely to maintain them after pituitary senescence and the somatopause. Autocrine or paracrine actions of GH are, however, sometimes mediated through different signaling mechanisms to those mediating its endocrine actions and these may promote oncogenesis. Extrapituitary GH may thus be of physiological and pathophysiological significance.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

Growth hormone promotes axon growth in the developing nervous system

Postnatally, endocrine GH is primarily produced by pituitary somatotrophs. GH is, however, also produced in extrapituitary sites, including tissues of the developing nervous system such as the neural retina. Whereas GH roles in the nervous system are starting to emerge, they are still largely unknown. We show here that GH in the neural retina is mainly present in the axons of retinal ganglion cells (RGCs) in embryonic day (E) 4-12 chick embryos, but it is no longer present at E14-18. This temporal window corresponds to the period of RGC axon growth. GH receptor mRNA was also detected within cells of the E7 RGC layer and GH receptor protein colocalized with GH in RGC axons. The possibility that GH promotes axon growth was thus investigated. Exogenous GH induced a significant increase in axon elongation at 10(-9) and 10(-6) M in E7 RGC culture purified by immunopanning. RNA interference-mediated gene silencing was used to examine whether endogenous GH similarly alters axon outgrowth. The ability of GH small-interfering RNA to knock down GH was first tested using HEK cells on a LacZ-cGH expression plasmid and found to reach 90%. Upon transfection of GH small-interfering RNA to immunopanned RGC culture, a 63% knockdown of endogenous GH was detected and RGC axon length was found to be reduced by 40%. Taken together, these data suggest that GH acts as an autocrine or paracrine signaling molecule to promote axon growth in a developing nervous tissue, the neural retina of chick embryos.

MAP dendrimer elicits antibodies for detecting rat and mouse GH-binding proteins

The membrane-bound rat GH-R and an alternatively spliced isoform, the soluble rat GH-BP, are comprised of identical N-terminal GH-binding domains; however, their C-terminal sequences differ. Immunological reagents are needed to distinguish between the two isoforms in order to understand their respective roles in mediating the actions of GH. Accordingly, a tetravalent MAP dendrimer with four identical branches of a C-terminal peptide sequence of the rat GH-BP (GH-BP(263-279)) was synthesized and used as an immunogen in rabbits. Solid-phase peptide synthesis of four GH-BP(263-279) segments onto a tetravalent Lys(2)-Lys-beta-Ala-OH core peptide was carried out using Fmoc chemistry. The mass of the RP-HPLC-purified synthetic product, 8398 Da, determined by ESI-MS, was identical to expected mass. Three anti-rat GH-BP(263-279) MAP antisera, BETO-8039, BETO-8040, and BETO-8041, at dilutions of 10(-3), recognized both the rat GH-BP(263-279) MAP and recombinant mouse GH-BP with ED(50)s within a range of 5-10 fmol, but did not cross-react with BSA in dot blot analyses. BETO-8041 antisera (10(-3) dilution) recognized GH-BPs of rat serum and liver having M(r)s ranging from 35 to 130 kDa, but did not recognize full-length rat GH-Rs. The antisera also detected recombinant mouse GH-BPs. In summary, the tetravalent rat GH-BP(263-279) MAP dendrimer served as an effective immunogenic antigen in eliciting high titer antisera specific for the C-termini of both rat and mouse GH-BPs. The antisera will facilitate studies aimed at improving our understanding of the biology of GH-BPs.

Protein expression profiling during chick retinal maturation: a proteomics-based approach

Background

The underlying pathways that drive retinal neurogenesis and synaptogenesis are still relatively poorly understood. Protein expression analysis can provide direct insight into these complex developmental processes. The aim of this study was therefore to employ proteomic analysis to study the developing chick retina throughout embryonic (E) development commencing at day 12 through 13, 17, 19 and post-hatch (P) 1 and 33 days.

Results

2D proteomic and mass spectrometric analysis detected an average of 1514 spots per gel with 15 spots demonstrating either modulation or constitutive expression identified via MS. Proteins identified included alpha and beta-tubulin, alpha enolase, B-creatine kinase, gamma-actin, platelet-activating factor (PAF), PREDICTED: similar to TGF-beta interacting protein 1, capping protein (actin filament muscle Z line), nucleophosmin 1 (NPM1), dimethylarginine dimethylaminohydrolase, triosphoaphate isomerase, DJ1, stathmin, fatty acid binding protein 7 (FABP7/B-FABP), beta-synuclein and enhancer of rudimentary homologue.

Conclusion

This study builds upon previous proteomic investigations of retinal development and represents the addition of a unique data set to those previously reported. Based on reported bioactivity some of the identified proteins are most likely to be important to normal retinal development in the chick. Continued analysis of the dynamic protein populations present at the early stages and throughout retinal development will increase our understanding of the molecular events underpinning retinogenesis.