Local overexpression of GH and GH/IGF1 effects in the adult mouse hippocampus

The role of growth hormone in hippocampal function

Growth hormone is a multifunctional molecule with broad cellular targets. This pituitary hormone is currently used as a therapeutic agent against several brain injuries due to its neurotrophic activity. The hippocampus is one of the brain regions where the growth hormone plays a role in normal and pathologic conditions. This brain structure is associated with several cognitive functions such as learning, memory, and mood, which are frequently affected by brain traumatism. The present chapter describes the experimental and clinical evidence that supports a central role of growth hormone in the hippocampus functionality.

Effects of Growth Hormone Treatment and Rehabilitation in Incomplete Chronic Traumatic Spinal Cord Injury: Insight from Proteome Analysis

Despite promising advances in the medical management of spinal cord injury (SCI), there is still no available effective therapy to repair the neurological damage in patients who experience this life-transforming condition. Recently, we performed a phase II/III placebo-controlled randomized trial of safety and efficacy of growth hormone (GH) treatment in incomplete chronic traumatic spinal cord injury. The main findings were that the combined treatment of GH plus rehabilitation treatment is feasible and safe, and that GH but not placebo slightly improves the SCI individual motor score. Moreover, we found that an intensive and long-lasting rehabilitation program per se increases the functional outcome of SCI individuals. To understand the possible mechanisms of the improvement due to GH treatment (motor score) and due to rehabilitation (functional outcome), we used a proteomic approach. Here, we used a multiple proteomic strategy to search for recovery biomarkers in blood plasma with the potential to predict response to somatropin treatment and to delayed intensive rehabilitation. Forty-six patients were recruited and followed for a minimum period of 1 year. Patients were classified into two groups based on their treatment: recombinant somatropin (0.4 mg) or placebo. Both groups received rehabilitation treatment. Our strategy allowed us to perform one of the deepest plasma proteomic analyses thus far, which revealed two proteomic signatures with predictive value: (i) response to recombinant somatropin treatment and (ii) response to rehabilitation. The proteins implicated in these signatures are related to homeostasis, inflammation, and coagulation functions. These findings open novel possibilities to assess and therapeutically manage patients with SCI, which could have a positive impact on their clinical response.

Voluntary wheel running delays brain atrophy in aged mice

BACKGROUND:

Physical exercises have been shown to be a surprisingly effective strategy to take advantage of the brain’s natural capacity for plasticity, and prevent brain degeneration in mouse histological studies. In vivo magnetic resonance microscopy (MRM) provides highly resolved anatomical images and allows quantitative assessment of brain atrophy in the aged mouse model.

OBJECTIVE:

The aim of the present study was to investigate, through the effects of 10 weeks voluntary wheel running, the mouse’s brain atrophy.

METHODS:

Sixteen C57BL/6J mice, aged 21 months, were randomized to the exercise or sedentary group. Each mouse was scanned in a 7.0-T MRM scanner at two time points: 22 months old baseline and a follow-up three months later. Multi-atlas based brain segmentation approach was used to obtain volumes of 39 brain regions.

RESULTS:

The results showed that mice in the exercise group had less brain atrophy compared with the mice in the sedentary group.

CONCLUSIONS:

The results provide new insights into exercise induced brain plasticity in aged animals.

The Role of Insulin-Like Growth Factors and Insulin-Like Growth Factor-Binding Proteins in the Nervous System

The insulin-like growth factors (IGF-I and IGF-II) and their receptors are widely expressed in nervous tissue from early embryonic life. They also cross the blood brain barriers by active transport, and their regulation as endocrine factors therefore differs from other tissues. In brain, IGFs have paracrine and autocrine actions that are modulated by IGF-binding proteins and interact with other growth factor signalling pathways. The IGF system has roles in nervous system development and maintenance. There is substantial evidence for a specific role for this system in some neurodegenerative diseases, and neuroprotective actions make this system an attractive target for new therapeutic approaches. In developing new therapies, interaction with IGF-binding proteins and other growth factor signalling pathways should be considered. This evidence is reviewed, gaps in knowledge are highlighted, and recommendations are made for future research.

Different modes of GH administration influence gene expression in the male rat brain

The endogenous secretion pattern in males of GH is episodic in rats and in humans, whereas GH administration is usually even. Different types of GH administration have different effects on body mass, longitudinal bone growth, and liver metabolism in rodents, whereas possible effects on brain plasticity have not been investigated. In this study, GH was administered as a continuous infusion or as two daily injections in hypophysectomized male rats. Thirteen transcripts previously known to respond to GH in the hippocampus and parietal cortex (cortex) were assessed by RT-PCR. To investigate the effects of type of GH administration on several transcripts with different variations, and categories of transcripts (neuron-, glia-, and GH-related), a mixed model analysis was applied. Accordingly, GH injections increased overall transcript abundance more than GH infusions (21% in the hippocampus, P<0.001 and 10% in the cortex, P=0.09). Specifically, GH infusions and injections robustly increased neuronal hemoglobin beta (Hbb) expression significantly (1.8- to 3.6-fold), and GH injections were more effective than GH infusions in increasing Hbb in the cortex (41%, P=0.02), whereas a 23% difference in the hippocampus was not significant. Also cortical connexin 43 was higher in the group with GH injections than in those with GH infusions (26%, P<0.007). Also, there were differences between GH injections and infusions in GH-related transcripts of the cortex (23%, P=0.04) and glia-related transcripts of the hippocampus (15%, P=0.02). Thus, with the exception of Hbb there is a moderate difference in responsiveness to different modes of GH administration.

Expression and function of growth hormone in the nervous system: a brief review

There is increasing evidence that growth hormone (GH) expression is not confined exclusively to the pituitary somatotrophs as it is synthesized in many extrapituitary locations. The nervous system is one of those extrapituitary sites. In this brief review we summarize data that substantiate the expression, distribution and characterization of neural GH and detail its roles in neural function, including cellular growth, proliferation, differentiation, neuroprotection and survival, as well as its functional roles in behavior, cognition and neurotransmission. Although systemic GH may exert some of these effects, it is increasingly evident that locally expressed neural GH, acting through intracrine, autocrine or paracrine mechanisms, may also be causally involved as a neurotrophic factor.