Nutrition-induced catch-up growth increases hypoxia inducible factor 1alpha RNA levels in the growth plate

Nutrient and Hormonal Effects on Long Bone Growth in Healthy and Obese Children: A Literature Review

Longitudinal bone growth is mediated through several mechanisms including macro- and micronutrients, and endocrine and paracrine hormones. These mechanisms can be affected by childhood obesity as excess adiposity may affect signaling pathways, place undue stress on the body, and affect normal physiology. This review describes the physiology of the epiphyseal growth plate, its regulation under healthy weight and obesity parameters, and bone pathology following obesity. A literature review was performed utilizing PubMed, PMC, NIH, and the Cochrane Database of Systematic Reviews pertinent to hormonal and nutritional effects on bone development, child obesity, and pathologic bone development related to weight. The review indicates a complex network of nutrients, hormones, and multi-system interactions mediates long bone growth. As growth of long bones occurs during childhood and the pubertal growth spurt, pediatric bones require adequate levels of minerals, vitamins, amino acids, and a base caloric supply for energy. Recommendations should focus on a nutrient-dense dietary approach rather than restrictive caloric diets to maintain optimal health. In conclusion, childhood obesity has profound multifaceted effects on the developing musculoskeletal system, ultimately causing poor nutritional status during development. Weight loss, under medical supervision, with proper nutritional guidelines, can help counteract the ill effects of childhood obesity.

Decrease in leptin mediates rat bone metabolism impairments during high-fat diet-induced catch-up growth by modulating the OPG/RANKL balance

Due to catch-up growth (CUG), there are adverse effects on human health. However, there is little information about its influence on bone metabolism. This study aimed to investigate the effects of leptin on bone metabolism and formation during high-fat diet (HFD)-induced CUG. We randomly divided male Wistar rats (5 weeks old) into four groups: control (CTL), caloric restriction and normal chow (RN), caloric restriction (4 weeks), and HFD (RH), and RH + leptin antagonist (RH + LEPA). We monitored body weights, biochemical markers, and epididymal and perirenal fat in these rats. We then performed Hematoxylin and Eosin (H&E) staining to evaluate bone metabolism. We detected osteoprotegerin (OPG) and receptor activator of nuclear factor-kappa b ligand (RANKL) by qRT-PCR and immunohistochemistry (IHC). We found that HFD increased the body weights in rats. In RN, RH, and RH + LEPA groups, major biochemical markers of bone metabolism in rat serum were significantly altered. We found that epididymal and perirenal fat tissues of RH and RH + LEPA groups were higher than those in the RN group. Severe bone formation impairment in the distal diaphysis and metaphysis of the left femora and lumbar vertebra was seen in the RH group compared to RN, which was even aggravated by a leptin antagonist. OPG in the left femora and lumbar vertebra was lower in RH than the RN group. The leptin antagonist decreased OPG during CUG in the RH group, whereas RANKL expression showed an opposite alteration. During HFD-induced CUG, bone formation was mediated by OPG and RANKL and was affected by the leptin content.

Adherence to healthy diet is related to better linear growth with open growth plate in adolescent girls

Nutritional status can affect the linear growth of bones during puberty by affecting growth plate (GP) chondrocytes. We hypothesized that there is a relationship between dietary patterns and bone age on girls who have experienced height loss. This cross-sectional study was conducted on 350 girls aged 12-13 years with open GP, and major dietary patterns were determined using the factor analysis method. Dual-energy x-ray absorptiometry measurement of participant's wrist was performed to determine GP openness and bone age. In the present study, 70.3% of participants had bone age below chronological age. Three major dietary patterns-healthy, high sugar and salt, and Western diet-were identified using findings of dietary intake. Adherence to the healthy diet led to significant increase in height, weight, body mass index, and other components of body composition such as lean body mass (P < .001). Among these dietary patterns, we found only a significant association between healthy diet and difference between bone and chronological age (B = -0.106). In the present study, adherence to a healthy diet was associated with increase in bone age (P = .02). Healthy dietary pattern with an emphasis on enough intake of plant protein and white meat was associated with better linear growth.

Undernutrition impairs the quality of growth plate and trabecular and cortical bones in growing rats1

Purpose

To investigate the effects of dietary restriction on the growth plate and long bone tissue in growing rats.

Methods

Sixty male Wistar rats were randomly assigned to two groups: Control (Con) and Diet-restricted (Res). After weaning, the Res rats were offered 50% of the chow ingested by the control (ad libitum food intake). The animals were subdivided into two subgroups with follow-ups up to 56 or 70 days. After euthanasia, the growth plate of tibias was analyzed by histomorphometry, micro-computed tomography, and mechanical test. The trabecular and compact bones were evaluated by histomorphometry, dual-energy X-ray absorptiometry, and micro-computed tomography (μCT). Real-time PCR was used to analyze gene expression.

Results

Although dietary restriction did not alter gene expression, several phenotypic changes were seen in the growth plate; i.e., decrease in volume, reduction in total area and height, decrease in the area ossified zones, mechanical weakening, reduction in mass of trabecular and cortical bone, lower bone density, deterioration of the trabecular and cortical microarchitecture, and trabeculae with lower collagen deposition.

Conclusion

Dietary restriction had severe detrimental effects on the growth plate and trabecular and cortical bone.

Undernutrition and growth in the developing world

PURPOSE OF REVIEW

Despite targeted interventions, an estimated 150.8 million children under 5 years globally are still stunted, of which more than half live in Asia and more than one-third live in Africa. This review summarizes our current knowledge regarding how longitudinal bone growth is regulated by nutritional intake in the developing world. Dietary macronutrients and micronutrients necessary for growth are also briefly reviewed.

RECENT FINDINGS

Recent advances include investigations of nutritionally sensitive regulators of growth as well as prospective evaluations of the role of specific dietary components on growth in order to better assess their impact.

SUMMARY

Further investigation is required to understand how nutrition impacts growth, the mechanisms underlying stunting and to optimize therapeutic strategies for children who are at risk for growth attenuation or are stunted in low and middle-income countries (LMICs).

Characterization of 5-Fluorouracil Daily Oral Dosing versus Dietary Restriction on Femoral Growth Plates in Rats

We evaluated the growth plates (GPs) of rats after a 14-day reduction in food consumption caused by either daily oral dosing with 5-fluorouracil (5-FU: a positive control reducing food consumption and affecting the GPs) or a direct reduction in food consumption to determine whether the observed changes were attributable to a direct effect of drug toxicity. Histomorphometric analyses of the femoral GP were performed for a nontreated (NT) control group, three groups treated with 5-FU (12, 15, and 18 mg/kg/day) and three groups with food intake restricted to levels corresponding to those consumed by the rats in the three 5-FU-treated groups. Compared with the NT group, the GP widths and the number of chondrocytes in the proliferative zone decreased significantly in all the 5-FU-treated groups and the dietary restriction groups. Importantly, no significant differences between the 5-FU-treated groups and the groups with matched dietary restrictions were seen for most parameters. Thus, the 14-day dietary restriction caused significant changes in the proliferative zone of the GP, and similar changes observed in the 5-FU-treated groups were presumed to result from the comparable reduction in food intake rather than being a direct toxic effect of the drug.

Leptin stimulates aromatase in the growth plate: limiting catch-up growth efficiency

Catch-up growth (CUG) in childhood is defined as periods of growth acceleration, after the resolution of growth attenuation causes, bringing the children back to their original growth trajectory. Sometimes, however, CUG is incomplete, leading to permanent growth deficit and short stature. The aim of this study was to investigate the mechanisms that limit nutritional-CUG. Specifically, we focused on the crosstalk between leptin, increased by re-feeding, and sex hormones, which increase with age. In vivo studies were performed in young male Sprague Dawley rats fed ad libitum or subjected to 10/36 days of 40% food restriction followed by 90-120 days of re-feeding. In vitro studies were performed on ATDC5 cells. Analyses of mRNA and protein levels were done using qPCR and Western blot, respectively. CUG was complete in body weight and humerus length in animals that were food-restricted for 10 days but not for those food-restricted for 36 days. In vitro studies showed that leptin significantly increased aromatase gene expression and protein level as well as the expression of estrogen and leptin receptors in a dose- and time-dependent manner. The effect of leptin on aromatase was direct and was mediated through the MAPK/Erk, STAT3 and PI3K pathways. The crosstalk between leptin and aromatase in the growth plate suggests that re-feeding during puberty may lead to increased estrogen level and activity, and consequently, irreversible premature epiphyseal growth plate closure. These results may have important implications for the development of novel treatment strategies for short stature in children.

Effect of Nutrition on Statural Growth

In children, proper growth and development are often regarded as a surrogate marker for good health. A complex system controls the initiation, rate, and cessation of growth, and thus gives a wonderful example of the interactions between genetics, epigenetics, and environmental factors (especially stress and nutrition). Malnutrition is considered a leading cause of growth attenuation in children. This review summarizes our current knowledge regarding the mechanisms linking nutrition and skeletal growth, including systemic factors, such as insulin, growth hormone, insulin-like growth factor-1, fibroblast growth factor-21, etc., and local mechanisms, including mTOR, miRNAs, and epigenetics. Studying the molecular mechanisms regulating skeletal growth may lead to the establishment of better nutritional and therapeutic regimens for more effective linear growth in children with malnutrition and growth abnormalities. 
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Beta Palmitate Improves Bone Length and Quality during Catch-Up Growth in Young Rats

Palmitic acid (PA) is the most abundant saturated fatty acid in human milk, where it is heavily concentrated in the sn-2-position (termed beta palmitate, BPA) and as such is conserved in all women, regardless of their diet or ethnicity, indicating its physiological and metabolic importance. We hypothesized that BPA improves the efficiency of nutrition-induced catch up growth as compared to sn-1,3 PA, which is present in vegetable oil. Pre-pubertal male rats were subjected to a 17 days food restriction followed by re-feeding for nine days with 1,3 PA or BPA-containing diets. We measured bone length, epiphyseal growth plate height (EGP, histology), bone quality (micro-CT and 3-point bending assay), and gene expression (Affymetrix). The BPA-containing diet improved most growth parameters: humeri length and EGP height were greater in the BPA-fed animals. Further analysis of the EGP revealed that the hypertrophic zone was significantly higher in the BPA group. In addition, Affymetrix analysis revealed that the diet affected the expression of several genes in the liver and EGP. Despite the very subtle difference between the diets and the short re-feeding period, we found a small but significant improvement in most growth parameters in the BPA-fed rats. This pre-clinical study may have important implications, especially for children with growth disorders and children with special nutritional needs.

Quantitative proteomics of rat livers shows that unrestricted feeding is stressful for proteostasis with implications on life span

Studies in young mammals on the molecular effects of food restriction leading to prolong adult life are scares. Here, we used high-throughput quantitative proteomic analysis of whole rat livers to address the molecular basis for growth arrest and the apparent life-prolonging phenotype of the food restriction regimen. Over 1800 common proteins were significantly quantified in livers of ad libitum, restriction- and re-fed rats, which summed up into 92% of the total protein mass of the cells. Compared to restriction, ad libitum cells contained significantly less mitochondrial catabolic enzymes and more cytosolic and ER HSP90 and HSP70 chaperones, which are hallmarks of heat- and chemically-stressed tissues. Following re-feeding, levels of HSPs nearly reached ad libitum levels. The quantitative and qualitative protein values indicated that the restriction regimen was a least stressful condition that used minimal amounts of HSP-chaperones to maintain optimal protein homeostasis and sustain optimal life span. In contrast, the elevated levels of HSP-chaperones in ad libitum tissues were characteristic of a chronic stress, which in the long term could lead to early aging and shorter life span.

Skeletal effect of casein and whey protein intake during catch-up growth in young male Sprague-Dawley rats

The aim of the present study was to determine whether the type of protein ingested influences the efficiency of catch-up (CU) growth and bone quality in fast-growing male rats. Young male Sprague-Dawley rats were either fed ad libitum (controls) or subjected to 36 d of 40 % food restriction followed by 24 or 40 d of re-feeding with either standard rat chow or iso-energetic, iso-protein diets containing milk proteins - casein or whey. In terms of body weight, CU growth was incomplete in all study groups. Despite their similar food consumption, casein-re-fed rats had a significantly higher body weight and longer humerus than whey-re-fed rats in the long term. The height of the epiphyseal growth plate (EGP) in both casein and whey groups was greater than that of rats re-fed normal chow. Microcomputed tomography yielded significant differences in bone microstructure between the casein and whey groups, with the casein-re-fed animals having greater cortical thickness in both the short and long term in addition to a higher trabecular bone fraction in the short term, although this difference disappeared in the long term. Mechanical testing confirmed the greater bone strength in rats re-fed casein. Bone quality during CU growth significantly depends on the type of protein ingested. The higher EGP in the casein- and whey-re-fed rats suggests a better growth potential with milk-based diets. These results suggest that whey may lead to slower bone growth with reduced weight gain and, as such, may serve to circumvent long-term complications of CU growth.

Growth attenuation is associated with histone deacetylase 10-induced autophagy in the liver

Our previous data suggested that the histone deacetylase (HDAC) SIRT1 is involved in mediating the effect of nutrition on growth. The aim of the present research was to study the mechanism by which additional HDACs may be involved in nutrition-induced linear growth. The in vivo studies were performed in young male Sprague-Dawley rats that were either fed ad libitum (AL) or subjected to 10days of 40% food restriction (RES) and then refed (CU). For in vitro studies, Huh7 hepatoma cells were used. Food restriction led to significant reduction in liver weight, concomitant with increased autophagy (i.e., a decrease in the level of P62 and an increase in the expression level of Ambra1 and Atg16L2 genes in the RES group). At the same time, we found that the level of HDAC10 was significantly increased. Overexpression of HDAC10 in Huh7 hepatoma cells led to reduced cell viability and increased autophagy as shown by increased conversion of LC3-I to LC3-II. An increase in the level of HDAC10 was also obtained when mTOR was inhibited by Rapamycin. siRNA directed against HDAC10 abolished the effect of Rapamycin on cell viability and Ambra1 and Atg16L2 increased expression. These results suggest that increased levels of HDAC10 may mediate the effect of malnutrition on growth attenuation and autophagy. Deciphering the role of epigenetic regulation in the nutrition-growth connection may pave the way for the development of new forms of treatment for children with growth disorders.

Nutritionally-induced catch-up growth

Malnutrition is considered a leading cause of growth attenuation in children. When food is replenished, spontaneous catch-up (CU) growth usually occurs, bringing the child back to its original growth trajectory. However, in some cases, the CU growth is not complete, leading to a permanent growth deficit. This review summarizes our current knowledge regarding the mechanism regulating nutrition and growth, including systemic factors, such as insulin, growth hormone, insulin- like growth factor-1, vitamin D, fibroblast growth factor-21, etc., and local mechanisms, including autophagy, as well as regulators of transcription, protein synthesis, miRNAs and epigenetics. Studying the molecular mechanisms regulating CU growth may lead to the establishment of better nutritional and therapeutic regimens for more effective CU growth in children with malnutrition and growth abnormalities. It will be fascinating to follow this research in the coming years and to translate the knowledge gained to clinical benefit.

Growth without growth hormone: can growth and differentiation factor 5 be the mediator?

Growth without growth hormone (GH) is often observed in the setup of obesity; however, the missing link between adipocytes and linear growth was until now not identified. 3T3L1 cells were induced to differentiate into adipocytes and their conditioned medium (CM) (adipocytes CM, CMA) was added to metatarsals bone culture and compared to CM derived from undifferentiated cells. CMA significantly increased metatarsals bone elongation. Adipogenic differentiation increased the expression of growth and differentiation factor (GDF)-5, also found to be secreted into the CMA. GDF-5 significantly increased metatarsal length in culture; treatment of the CMA with anti-GDF-5 antibody significantly reduced the stimulatory effect on bone length. The presence of GDF-5 receptor (bone morphogenetic protein receptor; BMPR1) in metatarsal bone was confirmed by immunohistochemistry. Animal studies in rodents subjected to food restriction followed by re-feeding showed an increase in GDF-5 serum levels concomitant with nutritional induced catch up growth. These results show that adipocytes may stimulate bone growth and suggest an additional explanation to the growth without GH phenomenon.

Bone quality is affected by food restriction and by nutrition-induced catch-up growth

Growth stunting constitutes the most common effect of malnutrition. When the primary cause of malnutrition is resolved, catch-up (CU) growth usually occurs. In this study, we have explored the effect of food restriction (RES) and refeeding on bone structure and mechanical properties. Sprague-Dawley male rats aged 24 days were subjected to 10 days of 40% RES, followed by refeeding for 1 (CU) or 26 days long-term CU (LTCU). The rats fed ad libitum served as controls. The growth plates were measured, osteoclasts were identified using tartrate-resistant acid phosphatase staining, and micro-computed tomography (CT) scanning and mechanical testing were used to study structure and mechanical properties. Micro-CT analysis showed that RES led to a significant reduction in trabecular BV/TV and trabecular number (Tb.N), concomitant with an increase in trabecular separation (Tb.Sp). Trabecular BV/TV and Tb.N were significantly greater in the CU group than in the RES in both short- and long-term experiments. Mechanical testing showed that RES led to weaker and less compliant bones; interestingly, bones of the CU group were also more fragile after 1 day of CU. Longer term of refeeding enabled correction of the bone parameters; however, LTCU did not achieve full recovery. These results suggest that RES in young rats attenuated growth and reduced trabecular bone parameters. While nutrition-induced CU growth led to an immediate increase in epiphyseal growth plate height and active bone modeling, it was also associated with a transient reduction in bone quality. This should be taken into consideration when treating children undergoing CU growth.

A serum component mediates food restriction-induced growth attenuation

Proper nutrition in terms of calories and essential food components is required to maximize longitudinal growth in children. Our previous study showed that prepubertal male rats subjected to 10 days of 40% food restriction (RES) exhibited a dramatic reduction in weight and epiphyseal growth plate height, as well as changes in gene expression and microRNAs (miRNAs) in the epiphyseal growth plate. These findings reversed rapidly after renewal of the regular food supply (catch-up [CU]). To further elucidate the mechanisms underlying the nutrition-growth association, serum collected from the RES and CU rats and control rats fed ad libitum (AL) was added to the culture medium of the chondrocyte cell line ATDC5 (instead of fetal calf serum). Serum from the RES group induced a reduction in cell viability (25%, P < .05) concomitant with an increase in cell differentiation compared with that for the AL group serum. The most interesting observation, in our opinion, was the significant reduction in the expression of specific miRNAs, including the chondro-specific miR-140. These effects were not observed for serum from refed (CU) rats. Serum levels of IGF-I, leptin, and fibroblast growth factor 21 were reduced by food restriction. The addition of IGF-I and leptin to the culture increased cell viability, whereas fibroblast growth factor 21 reduced it, suggesting the involvement of IGF-I, leptin, and possibly other still unidentified serum factors in chondrocyte cell growth. In conclusion, specific miRNAs respond to nutritional cues, and these effects are mediated by serum-borne factors. These results may promote the development of superior interventions for children with malnutrition and growth abnormalities.

Growth cartilage expression of growth hormone/insulin-like growth factor I axis in spontaneous and growth hormone induced catch-up growth

INTRODUCTION

Catch-up growth following the cessation of a growth inhibiting cause occurs in humans and animals. Although its underlying regulatory mechanisms are not well understood, current hypothesis confer an increasing importance to local factors intrinsic to the long bones' growth plate (GP).

AIM

The present study was designed to analyze the growth-hormone (GH)-insulin-like growth factor I (IGF-I) axis in the epiphyseal cartilage of young rats exhibiting catch-up growth as well as to evaluate the effect of GH treatment on this process.

MATERIAL AND METHODS

Female Sprague-Dawley rats were randomly grouped: controls (group C), 50% diet restriction for 3 days+refeeding (group CR); 50% diet restriction for 3 days+refeeding & GH treatment (group CRGH). Analysis of GH receptor (GHR), IGF-I, IGF-I receptor (IGF-IR) and IGF binding protein 5 (IGFBP5) expressions by real-time PCR was performed in tibial growth plates extracted at the time of catch-up growth, identified by osseous front advance greater than that of C animals.

RESULTS

In the absence of GH treatment, catch-up growth was associated with increased IGF-I and IGFBP5 mRNA levels, without changes in GHR or IGF-IR. GH treatment maintained the overexpression of IGF-I mRNA and induced an important increase in IGF-IR expression.

CONCLUSIONS

Catch-up growth that happens after diet restriction might be related with a dual stimulating local effect of IGF-I in growth plate resulting from overexpression and increased bioavailability of IGF-I. GH treatment further enhanced expression of IGF-IR which likely resulted in a potentiation of local IGF-I actions. These findings point out to an important role of growth cartilage GH/IGF-I axis regulation in a rat model of catch-up growth.

MicroRNAs in the growth plate are responsive to nutritional cues: association between miR-140 and SIRT1

MicroRNAs (miRNAs) have been reported to be involved in a variety of functions, including skeletal development and longitudinal growth. The aim of this study was to investigate the role of miRNAs in food-restriction-induced growth attenuation and nutrition-induced catch-up growth in the epiphyseal growth plate (EGP). Prepubertal rats were fed ad libitum or were subjected to 40% food restriction for 10 days followed by a renewal of the regular food supply. At sacrifice, tibial EGPs were excised, and the total RNA was extracted and loaded on miRNA microarrays. The miRNA microarray yielded more than 400 miRNAs that are expressed in the EGP of mature animals. Results were confirmed by quantitative polymerase chain reaction. Chondrocyte-specific miR-140-3p showed the highest expression in the mature EGP, and it was one of the few miRNAs that were significantly reduced following nutrition restriction. Changes in predicted miRNA targets were then followed with Western immunoblotting. Direct binding was demonstrated using exogenous miRNA, the 3'UTR of the target mRNA and a luciferase reporter assay. Nutrition restriction induced an increase in the level of the miR-140-3p target, NAD+-dependent SIRT1. This study is the first to show that SIRT1 and miRNAs expressed in the mature EGP are responsive to nutritional cues. Nutrition-induced epigenetic regulation of growth activates two parts of the epigenetic world - miRNAs and histone deacetylases - that are interconnected. Deciphering the role of epigenetic regulation in growth may open a new era of research and pave the way for the development of new treatments for children with growth disorders.

Nutrition and bone growth in pediatrics

Children's growth is a hallmark of their normal development and the association between nutrition and linear growth in children is well accepted. Growth requires an adequate supply of many different nutritional factors, some form the "building materials," whereas others play regulatory roles. In this article we describe the growth of the growth plate and discuss the role of nutritional affected hormones on this process. In addition we describe the effect of local regulators and nutritional factors on the growth process and suggest the involvement of new regulatory factors in the translation of nutrition to growth.

Homozygous microdeletion of the POU1F1, CHMP2B, and VGLL3 genes in chromosome 3--a novel syndrome

Microdeletion syndromes include numerous syndromic phenotypes associated with intellectual disability and dysmorphic features. We report on a patient with a novel microdeletion of chromosomal region 3p11.2-p12.1 containing POU1F1, chromatin-modifying protein 2B (CHMP2B), and vestigial-like 3 (VGLL3) genes. Our patient was diagnosed as having a neonatal multiple pituitary hormone [growth hormone (GH), thyroid-stimulating hormone (TSH), and prolactin] deficiency. In addition to the typical findings associated with these hormonal deficiencies, she exhibited clinical features resembling those of Laron syndrome (frontal bossing, saddle nose, small chin, blue sclera, and acromicria), with moderate intellectual disability. She also displayed an unusual growth pattern characterized by unresponsiveness to high doses of GH replacement therapy during infancy and early childhood and an accelerated growth rate beginning at the age of 4.5 years. Insulin-like growth factor (IGF)-1 levels were consistently extremely low or undetectable. Extensive medical and genetic analysis ruled out primary and secondary GH insensitivity. The distinct phenotype and the peculiar growth pattern observed in this affected patient, not reported to have been observed in other cases with POU1F1 gene inactivity, suggest that the other two deleted genes play a possible role in the development of this syndrome. This hypothesis may be supported by the fact that both the CHMP2B and VGLL3 genes are expressed in the liver and the growth plate, the two main target organs of the GH/IGF-1 axis. The homozygous deletion of the CHMP2B gene, previously associated with frontotemporal dementia, may contribute to the intellectual disability observed in this patient.

Catch-up and targeted growth following variable duration protein restriction: effects on bone and body mass

Protein malnutrition leads to growth retardation that can be reversed through catch-up growth, once normative nutrition is restored. Because growth is a dynamic process, catch-up capacity is likely influenced by the maturity of the animal and/or the duration of the insult, in addition to the type of insult experienced. We compared length of malnutrition, sexual dimorphism, body mass, and skeletal growth. Eighty Rattus norvegicus were divided into 10 treatment groups (five diets; male and female) and followed for more than 1 year. At weaning, animals were placed on either a control or low-protein isocaloric diet. Three experimental groups were switched to the control diet at 40, 60, or 90 days. Beginning with 21 days of age, animals were weighed daily and radiographed throughout the study. To determine the presence of catch-up growth, growth rates (GRs) were calculated (linear regression) for 20-day time spans before and after diet changes and compared among treatment groups. Targeted growth was measured as final size or as the coefficient of variation with age. These results show that 1) protein-restricted animals experience catch-up growth with dietary rehabilitation; 2) for females, catch-up GRs are proportional to GRs in control animals at the same age as the timing of dietary rehabilitation but not for males; and 3) targeted growth was observed in some, but not all, aspects of anatomy. The length of the tibia and humerus was indistinguishable from controls, regardless of length of malnutrition or gender, whereas the ulna and male body mass exceeded control sizes. Although most measures decreased in variation with ontogeny, the tibia failed to do so. These results support a complex biological regulation of catch-up and targeted growth. The implications for selection are that flexible and responsive developmental trajectories may have an advantage over those programed into a single size.

Involvement of matrix metalloproteinases in the growth plate response to physiological mechanical load

Enzymes from the matrix metalloproteinase (MMP) family play a crucial role in growth-plate vascularization and ossification via proteolytic cleavage and remodeling of the extracellular matrix. Their regulation in the growth plate is crucial for normal matrix assembly. Endochondral ossification, which takes place at the growth plates, is influenced by mechanical loading. Using an in vivo avian model for mechanical loading, we have found increased blood penetration into the growth plates of loaded chicks. The purpose of this work was to study the involvement of MMP-2, -3, -9, -13, and -16 in the growth plate's response to loading and in the catch-up growth resulting from load release. We found that mechanical loading, as well as release from load, upregulated MMP-2, -9, and -13 expressions. In contrast, MMP-3, associated with cartilage injuries, and its associated protein connective tissue growth factor (CTGF), were downregulated by the load. However, after release from load, MMP-3 was upregulated and CTGF levels were elevated and caught up with the control. MMP-3 and CTGF were also downregulated after 60 min of mechanical stretching in vitro. These results demonstrate the central role of MMPs in the growth plate's response to mechanical loading, as well as in the catch-up growth followed load release.

Nutrition and bone growth in pediatrics

Children's growth is a hallmark of their normal development and the association between nutrition and linear growth in children is well accepted. Growth requires an adequate supply of many different nutritional factors, some form the "building materials," whereas others play regulatory roles. In this article we describe the growth of the growth plate and discuss the role of nutritional affected hormones on this process. In addition we describe the effect of local regulators and nutritional factors on the growth process and suggest the involvement of new regulatory factors in the translation of nutrition to growth.

Leptin and regulation of linear growth

PURPOSE OF REVIEW

Leptin, first identified as the product of the ob gene in leptin-deficient obese (ob/ob) mice, was originally described as a circulating hormone involved in feeding behavior and energy homeostasis. It was later found to be a pleiotropic hormone involved in the regulation of a variety of physiological processes. This review summarizes our recent understanding of the role of leptin as a linear growth-stimulating factor.

RECENT FINDINGS

Leptin was found to have mitogenic effects on numerous cell types in vivo and in vitro, including several cancer cells, cells of the immune system, as well as chondrocytes of the epiphyseal growth plate.

SUMMARY

Leptin stimulates linear growth by regulating the energy balance of the organism and by stimulating the production and secretion of growth hormone from the hypothalamus; at the same time, it is involved with bone remodeling and has a direct effect on the chondrocytes of the growth plate.