Insulin-like growth factor-I (IGF-I) has been shown to stimulate myoblast proliferation for a limited time after which serum is required to reactivate IGF-I-stimulated myoblast proliferation. The aim of these studies was to determine whether IGF-I can stimulate myoblast proliferation and/or inhibit apoptosis alone or whether co-factors are necessary. This was achieved by investigating the proliferative response of L6 myoblasts to IGF-I and horse serum (HS) and by examining the status of cells in terms of cell number, substrate adherence, cell viability and DNA laddering following incubation with IGF-I and HS. L6 myoblasts proliferate in response to IGF-I after 36 h is not due to accumulation of waste products or lack of IGF-I. The addition of a low level (1% v/v) of HS restores the ability of myoblasts to proliferate in response to IGF-I and this supports the existence of a mitogenic competence factor. Furthermore, myoblasts failing to proliferate in response to IGF-I after 36 h regain the capacity to respond to IGF-I for a further period of 36 h when exposed to fetal bovine serum. Following the initial (36 h) phase of IGF-I-stimulated proliferation, removal of both IGF-I and HS led to a dramatic (60%) reduction in the number of cells fully attached to the culture vessel, with 60% of the completely detached cells dead. Agarose gel electrophoresis of extracts from these detached cells revealed higher levels of DNA laddering than extracts prepared from attached cells with IGF-I present. This suggests that IGF-I acts as a survival factor by protecting cells from apoptosis. In conclusion these experiments support the presence of a mitogenic competence factor in horse serum, which restores the ability of cells to proliferate in response to IGF-I. Unlike proliferation, protection against apoptosis is achieved by IGF-I or HS independently of each other.
Napier JR, MF Thomas, M Sharma, SC Hodgkinson and JJ Bass
TS Udayakumar, DA Jeyaraj, M Rajalakshmi and RS Sharma
Rhesus monkey prostate epithelial cells from the cranial lobe were isolated and cultured in flasks coated either with collagen IV or laminin. The effects of stromal cell medium, androgens and growth factors on cell number, thymidine incorporation and secretory activity were assessed. The results indicate that dihydrotestosterone (DHT) and androstenedione have stimulatory influences on cell proliferation and secretion in coated flasks. DHT was more effective in increasing cell number but the induction of secretory activity was similar with both steroids. The combination of IGF-I and -II resulted in inducing better cell proliferation and secretory activity than the individual IGFs but, of the two IGFs, IGF-I was more effective than IGF-II. DHT with IGFs was more potent in inducing proliferation, differentiation and secretion than androstenedione. Even in the absence of steroids or growth factors, colony formation and confluence occurred in coated flasks but cell differentiation and secretion only to a limited extent. In conclusion, we were able to establish an in vitro primary culture of prostate epithelial cells from rhesus monkey using extracellular matrix proteins, steroids and growth factors as additional supplements. This culture system may be useful to study prostate cell physiology and to identify drugs that can inhibit cell proliferation.
F Jeanplong, JJ Bass, HK Smith, SP Kirk, R Kambadur, M Sharma and JM Oldham
The IGF axis is nutritionally sensitive in vivo and IGFs stimulate myoblast proliferation and differentiation in vitro, while myostatin inhibits these processes in vitro. We hypothesised that underfeeding would reversibly inhibit the myogenic activity of satellite cells in vivo together with decreased IGF-I and increased myostatin in muscle. Satellite cell activity was measured indirectly from the expression of proliferating cell nuclear antigen (PCNA) and the myogenic regulatory factors (MRFs), MyoD, Myf-5 and myogenin. Young sheep were underfed (30% of maintenance) and some killed after 1, 4, 12, 17, 21 and 22 weeks. Remaining underfed animals were then re-fed a control ration of pellets and killed after 2 days, and 1, 6 and 30 weeks. Expression of PCNA and MRFs decreased during the first week of underfeeding. This coincided with reduced IGF-I and myostatin mRNA, and processed myostatin. Subsequently, Myf-5, MyoD, myostatin mRNA and processed myostatin increased, suggesting that satellite cells may have become progressively quiescent. Long-term underfeeding caused muscle necrosis in some animals and IGF-I and MRF expression was increased in these, indicating the activation of satellite cells for muscle repair. Re-feeding initiated rapid muscle growth and increased expression of PCNA, IGF-I and the MRFs concurrently with decreased myostatin proteins. In conclusion, these data indicate that IGF-I and myostatin may work in a coordinated manner to regulate the proliferation, differentiation and quiescence of satellite cells in vivo.
K. B. DESAI, M. N. MEHTA, M. C. PATEL, S. M. SHARMA, L. RAMANNA and R. D. GANATRA
Two siblings, a brother (H. B.) and a sister (R. B.) with long standing goitres were investigated. Radioactive iodine uptake by the thyroid was increased and a significant portion of the plasma radioactive iodine was not extractable with butanol. Chromatography of butanol extracts of serum after radioactive iodine administration showed distinct peaks of triiodothyronine and thyroxine. Microscopic examination of the surgical specimens of the goitres showed Hürthle cell carcinoma with follicles devoid of colloid in both specimens. Sucrose density gradient centrifugation, gel filtration on Sephadex G-200, salting out procedures, starch gel electrophoresis and immunological tests of the supernatant soluble fraction of thyroid homogenates showed a lack of thyroglobulin. Further fractionation of the soluble proteins showed that albumin was apparently involved in the synthesis of thyroid hormones in the absence of thyroglobulin.
M. J. VandeHaar, B. M. Moats-Staats, M. L. Davenport, J. L. Walker, J.-M. Ketelslegers, B. K. Sharma and L. E. Underwood
The serum concentration of insulin-like growth factor-I (IGF-I) is reduced in growing rats fed a low-protein diet, and this decrease is age-dependent, being more pronounced in younger animals. To determine whether this decrease in serum IGF-I is related to a decrease in IGF-I mRNA, growing female rats were given free access to either a 15% protein-sufficient or a 5% protein-deficient diet for 1 week. Protein restriction in 4-week-old rats decreased body weight gain by 44% (P < 0·001) compared with 4-week controls), serum IGF-I concentration by 67% (P < 0·001) and liver IGF-I mRNA abundance by 51% (P < 0·001). During week 6, protein restriction for 1 week resulted in a 20% increase in food intake with no change in weight gain, a 38% reduction in serum IGF-I (P < 0·001 compared with 6-week controls) and a 39% decrease in liver IGF-I mRNA (P < 0·001). The serum IGF-I concentration was highly correlated (r = 0·80; P < 0·001) with the hepatic IGF-I mRNA concentration. Skeletal muscle IGF-I mRNA abundance was also decreased significantly by protein restriction (37% at week 4, P<0·001, and 24% at week 6, P < 0·01) and was closely correlated (r = 0·71; P < 0·001) with body weight gain. Liver GH-binding protein and GH receptor mRNA abundance were reduced by 1 week of protein deprivation at week 6 but not at week 4. We conclude that the reduced serum IGF-I of young rats fed a low-protein diet is due, in part, to reduced liver IGF-I mRNA, and that these changes are not dependent on GH binding. Decreased skeletal muscle IGF-I mRNA during protein restriction is consistent with an autocrine/paracrine action of IGF-I in muscle.
Journal of Endocrinology (1991) 130, 305–312
Craig S Nunemaker, H Grace Chung, Gretchen M Verrilli, Kathryn L Corbin, Aditi Upadhye and Poonam R Sharma
Proinflammatory cytokines are thought to play a significant role in the pathogenesis of type 2 diabetes (T2D) and are elevated in the circulation even before the onset of the disease. However, the full complement of cytokines involved in the development of T2D is not known. In this study, 32 serum cytokines were measured from diabetes-prone BKS.Cg-m + / + Lepr db/J (db/db) mice and heterozygous age-matched control mice at 5 weeks (non-diabetic/non-obese), 6–7 weeks (transitional-to-diabetes), or 11 weeks (hyperglycemic/obese) and then correlated with body weight, blood glucose, and fat content. Among these 32 cytokines, C-X-C motif ligand 1 (CXCL1) showed the greatest increase (+78%) in serum levels between db/db mice that were hyperglycemic (blood glucose: 519±23 mg/dl, n=6) and those that were non-hyperglycemic (193±13 mg/dl, n=8). Similarly, increased CXCL1 (+68%) and CXCL5 (+40%) were associated with increased obesity in db/db mice; note that these effects could not be entirely separated from age. We then examined whether islets could be a source of these chemokines. Exposure to cytokines mimicking low-grade systemic inflammation (10 pg/ml IL1β+20 pg/ml IL6) for 48 h upregulated islet CXCL1 expression by 53±3-fold and CXCL5 expression by 83±10-fold (n=4, P<0.001). Finally, overnight treatment with the combination of CXCL1 and CXCL5 at serum levels was sufficient to produce a significant decrease in the peak calcium response to glucose stimulation, suggesting reduced islet function. Our findings demonstrated that CXCL1 and CXCL5 i) are increased in the circulation with the onset of T2D, ii) are produced by islets under stress, and iii) synergistically affect islet function, suggesting that these chemokines participate in the pathogenesis of T2D.
Rita Sharma, Quyen Luong, Vishva M Sharma, Mitchell Harberson, Brian Harper, Andrew Colborn, Darlene E Berryman, Niels Jessen, Jens Otto Lunde Jørgensen, John J Kopchick, Vishwajeet Puri and Kevin Y Lee
Growth hormone (GH) has long been known to stimulate lipolysis and insulin resistance; however, the molecular mechanisms underlying these effects are unknown. In the present study, we demonstrate that GH acutely induces lipolysis in cultured adipocytes. This effect is secondary to the reduced expression of a negative regulator of lipolysis, fat-specific protein 27 (FSP27; aka Cidec) at both the mRNA and protein levels. These effects are mimicked in vivo as transgenic overexpression of GH leads to a reduction of FSP27 expression. Mechanistically, we show GH modulation of FSP27 expression is mediated through activation of both MEK/ERK- and STAT5-dependent intracellular signaling. These two molecular pathways interact to differentially manipulate peroxisome proliferator-activated receptor gamma activity (PPARγ) on the FSP27 promoter. Furthermore, overexpression of FSP27 is sufficient to fully suppress GH-induced lipolysis and insulin resistance in cultured adipocytes. Taken together, these data decipher a molecular mechanism by which GH acutely regulates lipolysis and insulin resistance in adipocytes.
C Chakraborty, S Sharma, N Katsumata, L J Murphy, I C Schroedter, M C Robertson, R P C Shiu and H G Friesen
The secretion of peptide 23 by rat pituitary cells is stimulated by growth hormone-releasing hormone and inhibited by somatostatin. Recent cloning of the cognate cDNA for peptide 23 revealed that it is identical to pancreatitis-associated protein (PAP). In the present study, the clearance and tissue uptake of recombinant peptide 23/PAP in normal adult male rats was assessed. The plasma half-life of recombinant peptide 23/PAP was 4·8 ±1·4 (s.d.) min. Maximal accumulation of radiolabelled peptide 23/PAP was observed in the kidney, stomach, small intestine and pancreas whereas negligible uptake was seen in the liver, lung or heart. Peptide 23/PAP was detected in a variety of tissue extracts using a radioimmunoassay. Extracts of ileum contained the highest concentrations of peptide 23/PAP. In situ hybridization analysis showed that peptide 23/PAP mRNA was highly expressed in the columnar epithelial cells of ileum, jejunum and duodenum. These observations demonstrate that peptide 23/PAP, a protein previously thought to be of pituitary origin, is widely expressed in the gastrointestinal tract and that it is rapidly removed from the circulation by the kidney and by tissues which express peptide 23/PAP.
Journal of Endocrinology (1995) 145, 461–469