Muscle regeneration. The effect of hypophysectomy on cell proliferation and expression of insulin-like growth factor-I

Promising applications of human-derived saliva biomarker testing in clinical diagnostics

Saliva testing is a vital method for clinical applications, for its noninvasive features, richness in substances, and the huge amount. Due to its direct anatomical connection with oral, digestive, and endocrine systems, clinical usage of saliva testing for these diseases is promising. Furthermore, for other diseases that seeming to have no correlations with saliva, such as neurodegenerative diseases and psychological diseases, researchers also reckon saliva informative. Tremendous papers are being produced in this field. Updated summaries of recent literature give newcomers a shortcut to have a grasp of this topic. Here, we focused on recent research about saliva biomarkers that are derived from humans, not from other organisms. The review mostly addresses the proceedings from 2016 to 2022, to shed light on the promising usage of saliva testing in clinical diagnostics. We recap the recent advances following the category of different types of biomarkers, such as intracellular DNA, RNA, proteins and intercellular exosomes, cell-free DNA, to give a comprehensive impression of saliva biomarker testing.

The influence of growth hormone status on physical impairments, functional limitations, and health-related quality of life in adults

The availability of recombinant human GH and somatostatin analogs has resulted in widespread treatment for adults with GH deficiency (GHD) and those with GH excess (acromegaly). Despite being at opposite ends of the spectrum in terms of their GH/IGF-I axis, both of these populations experience overlapping somatic impairments. Adults with untreated GHD have low circulating levels of IGF-I that manifest as altered body composition with increased fat and reduced lean body and skeletal muscle mass. At the other end of the spectrum, adults with GH excess, who have elevated levels of IGF-I, also have altered body composition. Impairments that result from disorders of either GHD or GH excess are both associated with increased functional limitations, such as reduced ability to walk quickly for prolonged periods, and poorer health-related quality of life (HR-QoL). Adults with untreated GHD and GH excess both commonly complain of excessive fatigue that seems to be associated more with impaired aerobic than muscular performance. Several studies have documented that administration of GH or somatostatin analogs to adults with GHD or GH excess, respectively, ameliorates abnormal biochemical profile and the associated somatic impairments. However, whether these improvements translate into improved physical function in adults with GHD or GH excess remains largely unknown, and their impact on HR-QoL controversial. Review of placebo-controlled trials to date suggests that GH and somatostatin analogs have greater effects on gas exchange and aerobic performance than as anabolic agents on skeletal muscle mass and function. Future investigations should include dose-response studies to establish the optimal combination of pharmacological agents plus exercise required to improve not only biochemical markers but also physical function and HR-QoL in adults with GHD or GH excess.

IGF-I increases bone marrow contribution to adult skeletal muscle and enhances the fusion of myelomonocytic precursors

Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

Stem cell-mediated muscle regeneration is enhanced by local isoform of insulin-like growth factor 1

We investigated the mechanism whereby expression of a transgene encoding a locally acting isoform of insulin-like growth factor 1 (mIGF-1) enhances repair of skeletal muscle damage. Increased recruitment of proliferating bone marrow cells to injured MLC/mIgf-1 transgenic muscles was accompanied by elevated bone marrow stem cell production in response to distal trauma. Regenerating MLC/mIgf-1 transgenic muscles contained increased cell populations expressing stem cell markers, exhibited accelerated myogenic differentiation, expressed markers of regeneration and readily converted cocultured bone marrow to muscle. These data implicate mIGF-1 as a powerful enhancer of the regeneration response, mediating the recruitment of bone marrow cells to sites of tissue damage and augmenting local repair mechanisms.

Growth hormone administration produces a biphasic cellular muscle growth in weaning mice

The present study was undertaken to elucidate the effect of the exogenous administration of rhGH on the time course of the cellular muscle growth in male and female BALB/c mice fed 20% dietary protein between weaning and 50 days of age. Also, the efficiency of utilization of protein and energy intake to muscle DNA content and protein per cell (protein to DNA ratio) storage were studied. 120 weaned mice (21 d) were assigned to four groups based on rhGH-treatment (rhGH-treated: 7.4 ng x g(-1) BW and control: saline vehicle; via s.c. every two days) and gender. Feed intake was measured daily. At 25, 30, 35, 40, 45 and 50 days of age twenty mice were killed by cervical dislocation and the samples of gastrocnemius muscles were isolated, weighed and protein and DNA contents were measured. The rhGH administration caused a biphasic response altering the muscle cellular growth as a consequence of age-specific feed intake changes. The GH-induced fall of feed intake between 25 and 30 days of age caused decreases in muscle weight and myonuclei number (DNA), whereas muscle cell size was maintained. Later on, the self-controlled increase of feed intake led to the muscle weight recovery to control level, in spite of the irreversible DNA fall, as a consequence of the increase of cellular protein deposition and an enhancement of utilization of protein and energy intakes to deposit protein per cell. These results demonstrate that in spite of the initial (25-30 d of age) muscle DNA fall, rhGH-administration from weaning ensures the recovery of cellular muscle growth to control level through a compensatory muscle hypertrophy.

The pituitary-muscle axis in mdx dystrophic mice

As myogenesis, muscle growth and differentiation and growth factor expression are influenced by thyroid and growth hormone (GH) levels, it is important to investigate the possibility that altered activity of the pituitary-muscle axis prevents the lethal progression of mdx dystrophy and/or contributes to the muscle fiber hypertrophy of limb muscles. The ultrastructure of pituitary and thyroid tissues in age-matched control and mdx mice at 2 and 12 months of age was examined. Pituitary GH, and serum thyroid stimulating hormone (TSH), thyroid hormone (T4), and creatine kinase (CK) levels were measured. Mdx thyroid gland structure was similar to age-matched control glands. Mdx thyroid gland weighed significantly more than in age-matched controls, but was unchanged relative to body weight. TSH and T4 levels were not different from levels in control mice. High CK levels reflected the active dystrophy in mdx muscles. Somatotrophs in mdx pituitaries were hypertrophied in comparison to controls, indicating increased secretory activity, and pituitary GH was slightly but significantly greater in old mdx female mice compared to age-matched female controls. These observations rule out hypopituitary or hypothyroid function as a reason for the low impact of dystrophin deficiency in mdx muscles. Results suggest a contribution by raised GH to the fiber hypertrophy in mdx limb and heart muscle, which might also assist the large capacity for limb muscle regeneration in mdx mice.

Skeletal muscle satellite cells

Evidence now suggests that satellite cells constitute a class of myogenic cells that differ distinctly from other embryonic myoblasts. Satellite cells arise from somites and first appear as a distinct myoblast type well before birth. Satellite cells from different muscles cannot be functionally distinguished from one another and are able to provide nuclei to all fibers without regard to phenotype. Thus, it is difficult to ascribe any significant function to establishing or stabilizing fiber type, even during regeneration. Within a muscle, satellite cells exhibit marked heterogeneity with respect to their proliferative behavior. The satellite cell population on a fiber can be partitioned into those that function as stem cells and those which are readily available for fusion. Recent studies have shown that the cells are not simply spindle shaped, but are very diverse in their morphology and have multiple branches emanating from the poles of the cells. This finding is consistent with other studies indicating that the cells have the capacity for extensive migration within, and perhaps between, muscles. Complexity of cell shape usually reflects increased cytoplasmic volume and organelles including a well developed Golgi, and is usually associated with growing postnatal muscle or muscles undergoing some form of induced adaptive change or repair. The appearance of activated satellite cells suggests some function of the cells in the adaptive process through elaboration and secretion of a product. Significant advances have been made in determining the potential secretion products that satellite cells make. The manner in which satellite cell proliferative and fusion behavior is controlled has also been studied. There seems to be little doubt that cellcell coupling is not how satellite cells and myofibers communicate. Rather satellite cell regulation is through a number of potential growth factors that arise from a number of sources. Critical to the understanding of this form of control is to determine which of the many growth factors that can alter satellite cell behavior in vitro are at work in vivo. Little work has been done to determine what controls are at work after a regeneration response has been initiated. It seems likely that, after injury, growth factors are liberated through proteolytic activity and initiate an activation process whereby cells enter into a proliferative phase. After myofibers are formed, it also seems likely that satellite cell behavior is regulated through diffusible factors arising from the fibers rather than continuous control by circulating factors.(ABSTRACT TRUNCATED AT 400 WORDS)

Skeletal muscle regeneration in young rats is dependent on growth hormone

Skeletal muscle fibres have a well known ability to regenerate after different kinds of injury. This study was undertaken to establish if regenerating skeletal muscle is dependent on growth hormone (GH) in the same manner as normal, growing skeletal muscle in young rats. Muscle regeneration was achieved by injection of notexin into the soleus muscle. Initial necrosis, which included all muscle fibres, was followed by a rapid and uniform regeneration throughout the muscle. Cell proliferation was estimated by scintillation counting and autoradiography of incorporated [3H]thymidine, injected intravenously 1 h before killing, 7 or 27 days after the initiation of regeneration. GH deficiency was accomplished by hypophysectomy 4 days before the [3H]thymidine injection. Cell proliferation was diminished in both regenerating and normal muscle of the hypophysectomized rats compared to control and GH-substituted rats. After 7 days of regeneration the reduction of cell proliferation seen in hypophysectomized rats was less pronounced in the regenerating than in the normal muscle. These findings demonstrate that GH plays an important role for muscle regeneration in young rats, although other substances appear to be of greater importance during the early stages of regeneration.

IGF1 and 2 in two models of adrenal growth

Insulin-like growth factors (IGFs) 1 and 2 were measured in the adrenal glands of rats undergoing either compensatory growth following left unilateral adrenalectomy or adrenal regeneration following bilateral adrenal enucleation. In normal rat adrenal gland, the tissue concentration of IGF2 (7.45 +/- 0.99 pg/micrograms protein) wa higher than IGF1 (1.26 +/- 0.23 pg/micrograms protein), both peptides being more abundant in the inner zones of the adrenal gland compared to the capsule-glomerulosa. During compensatory growth of the right adrenal gland, IGF1 and 2 increased significantly compared with control right adrenal glands at 24 h following left unilateral adrenalectomy (P less than 0.001). At 68 h, the increase remained significant for IGF1 (P = 0.012). The two peptides were measured in the regenerating adrenal gland at 7, 14 and 21 days following bilateral enucleation. Whilst there was a trend towards an increase in the IGF1 and 2 content of regenerating adrenal glands, the increase was significant only for IGF2 in the left adrenal gland at 21 days following enucleation. Plasma IGF1 and 2 did not increase compared to controls during the experiments (110.97 +/- 1.95 and 46.33 ng/ml, respectively), suggesting that the changes in tissue IGF reflect increased local production during rapid growth of the adrenal gland.