Hepatocyte growth factor inhibits apoptosis after ischemic renal injury in rats.

Several studies have determined that growth factors, including hepatocyte growth factor (HGF), have a crucial role in the regenerative process of renal tubules after ischemic or toxic insult. Recent research has ascertained that as well as necrotic cell death, there is evidence of apoptosis after an acute renal injury. We attempted to determine the effect of HGF on apoptosis after ischemic renal injury in rats. We administered HGF or vehicle to 12 rats after ischemic insult and compared them with 6 sham-operated controls. Rats were killed at 48 hours, and histopathologic assessments were performed on the renal tissue. The microscale autoradiographic method was used for qualitative analysis of DNA fragmentation. This method was chosen over the widely used ethidium bromide-staining method because it increases the sensitivity of detection of apoptotic DNA. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling histopathologic staining was used to identify apoptosis in situ. Apoptotic changes were clearly shown by electron microscopy in vehicle-treated animals. Despite showing profound evidence of tubular necrosis, apoptotic changes were markedly reduced in HGF-treated animals compared with vehicle-treated animals. DNA-laddering analysis further confirmed the antiapoptotic effect of HGF. To our knowledge, this is the first in vivo illustration of the inhibitory activity of a growth factor on apoptosis in the setting of tubular necrosis. The role of apoptosis in the setting of acute renal failure has not been elucidated; thus, additional research is necessary to determine the significance of these findings.

Tubular catabolism of albumin is associated with the release of an inflammatory lipid.

Proteinuria and tubulointerstitial inflammation (TII) correlate with progression to renal failure in human glomerulonephritis. Various forms of experimental nephrotic syndrome are associated with TII. To study the genesis of TII, we utilized the model of albumin overload. Rats received intraperitoneal bovine serum albumin (BSA) for 1 to 14 days, developing heavy proteinuria. A predominantly macrophage interstitial infiltrate was present at days 3, 7 and 14. The urine of the rats contained a factor chemotactic for macrophages which partitioned into the organic phase with ethyl acetate extraction. TLC and HPLC characteristics were those of a novel, non-polar lipid. Supernatant from the culture of proximal tubule (PT) segments after in vivo or in vitro exposure to high concentrations of lipid-replete BSA showed chemotactic activity with similar chromatographic characteristics. PT cultured with delipidated BSA produced little activity. Thus, the generation of this inflammatory factor occurs as a consequence of tubular metabolism of albumin-borne fatty acids and may contribute to the development of proteinuria-associated TII.

Activation of insulin-like growth factor gene expression during work-induced skeletal muscle growth.

We have investigated the hypothesis that there is local regulation of insulin-like growth factor (IGF) gene expression during skeletal muscle growth. Compensatory hypertrophy was induced in the soleus, a predominantly slow-twitch muscle, and plantaris, a fast-twitch muscle, in 11- to 12-wk-old female Wistar rats by unilateral cutting of the distal gastrocnemius tendon. Animals were killed 2, 4, or 8 days later, and muscles of the nonoperated leg served as controls. Muscle weight increased throughout the experimental period, reaching 127% (soleus) or 122% (plantaris) of control values by day 8. In both growing muscles, IGF-I mRNA, quantitated by a solution-hybridization nuclease-protection assay, rose by nearly threefold on day 2 and remained elevated throughout the experimental period. IGF-II mRNA levels also increased over controls. A more dramatic response was seen in hypophysectomized rats, where IGF-I mRNA levels rose by 8- to 13-fold, IGF-II values by 3- to 7-fold, and muscle mass increased on day 8 to 149% (soleus) or 133% (plantaris) of the control contralateral limb. These results indicate that signals propagated during muscle hypertrophy enhance the expression of both IGF genes, that modulation of IGF-I mRNA levels can occur in the absence of growth hormone, and that locally produced IGF-I and IGF-II may play a role in skeletal muscle growth.

Dual regulation of insulin-like growth factor I expression during renal hypertrophy.

We examined the regulation of insulin-like growth factor I (IGF-I) in kidney during the renal hypertrophy produced by two different experimental models: growth hormone treatment of hypophysectomized rats and compensatory hypertrophy subsequent to unilateral nephrectomy. Immunostaining for IGF-I in collecting ducts was enhanced in kidneys from growth hormone-repleted hypophysectomized rats, and the levels of IGF-I mRNAs were increased. In compensatory hypertrophy, no enhancement of the intensity of immunostaining was observed in kidneys of nephrectomized rats until 5 days postnephrectomy, at which time immunostainable IGF-I was increased markedly in medullary collecting ducts of hypertrophied kidneys compared with kidneys from sham-operated animals. No difference in steady-state levels of any IGF-I mRNA species was detected in whole kidneys or in collecting ducts from nephrectomized or sham-operated rats at any time postnephrectomy. Our findings demonstrate an increase in both IGF-I mRNA and in immunostainable IGF-I in collecting duct in the setting of growth hormone-induced renal hypertrophy but suggest that other, possibly translational, mechanisms underlie the induction of IGF-I synthesis during compensatory hypertrophy.

Coordinate expression of insulin-like growth factor II and its receptor during muscle differentiation.

The role of polypeptide growth factors in promoting muscle differentiation is uncharacterized. We have used a fusing skeletal muscle cell line, C2, to examine the endogenous expression of one peptide, insulin-like growth factor II (IGF-II), and its receptor during differentiation. The synthesis of IGF-II is low during proliferation of myoblasts; IGF-II mRNA can be detected only through use of a highly sensitive solution-hybridization assay. Competition binding studies reveal that the IGF-II receptor is similarly nonabundant in myoblasts. During differentiation IGF-II mRNA rises rapidly. A nearly 4-fold increase is seen within 16 hr of onset of the differentiation process, and levels are 25 times higher than those in myoblasts by 96 hr, when myotubes have formed and muscle-specific alpha-actin mRNAs are synthesized. IGF-II accumulates in conditioned culture medium with similar kinetics. The expression of IGF-II receptors on the cell surface increases almost 6-fold 24 hr after the onset of differentiation and remains high. These studies suggest that IGF-II and its receptor are coordinately regulated during myogenic differentiation in C2 cells and that IGF-II may be an autocrine factor for skeletal muscle.