SUMMARY Catabolic conditions like chronic kidney disease (CKD) cause loss of muscle mass by unclear mechanisms. In muscle biopsies from CKD patients, we found activated Stat3 (p-Stat3) and hypothesized that p-Stat3 initiates muscle wasting. We created mice with muscle-specific knockout (KO) that prevents activation of Stat3. In these mice, losses of body and muscle weights were suppressed in models of CKD or acute diabetes. A small molecule that inhibits Stat3 activation produced similar responses suggesting a potential for translation strategies. Using C/EBPδ KO mice and C2C12 myotubes with knockdown of C/EBPδ or myostatin, we determined that p-Stat3 initiates muscle wasting via C/EBPδ, stimulating myostatin, a negative muscle growth regulator. C/EBPδ KO also improved survival of CKD mice. We verified that p-Stat3, C/EBPδ and myostatin were increased in muscles of CKD patients. The pathway from p-Stat3 to C/EBPδ to myostatin and muscle wasting could identify therapeutic targets that prevent muscle wasting.

Background:No reliable treatment exists for cancer-related muscle loss. Results: In muscles of mice with cancer, p-Stat3 stimulates proteolysis by activating caspase-3 and the ubiquitin-proteasome system through a C/EBP␦ and myostatin pathway. Conclusion: Inhibition of Stat3 suppresses cancer-induced muscle losses.Significance: A small-molecule Stat3 inhibitor could be integrated into therapeutic strategies for preventing cancer-induced muscle losses.

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) act on gonadal cells to promote steroidogenesis and gametogenesis. Clarifying the in vivo roles of LH and FSH permits a feasible approach to contraception involving selective blockade of gonadotropin action. One way to address these physiologically important problems is to generate mice with an isolated LH deficiency and compare them with existing FSH loss-of-function mice. To model human reproductive disorders involving loss of LH function and to define LH-responsive genes, we produced knockout mice lacking the hormone-specific LH␤-subunit. LH␤-null mice are viable but demonstrate postnatal defects in gonadal growth and function resulting in infertility. Mutant males have decreased testes size, prominent Leydig cell hypoplasia, defects in expression of genes encoding steroid biosynthesis pathway enzymes, and reduced testosterone levels. Furthermore, spermatogenesis is blocked at the round spermatid stage, causing a total absence of the elongated spermatids. Mutant female mice are hypogonadal and demonstrate decreased levels of serum estradiol and progesterone. Ovarian histology demonstrates normal thecal layer, defects in folliculogenesis including many degenerating antral follicles, and absence of corpora lutea. The defects in both sexes are not secondary to aberrant FSH regulation, because FSH levels were unaffected in null mice. Finally, both male and female null mice can be pharmacologically rescued by exogenous human chorionic gonadotropin, indicating that LH-responsiveness of the target cells is not irreversibly lost. Thus, LH␤ null mice represent a model to study the consequences of an isolated deficiency of LH ligand in reproduction, while retaining normal LH-responsiveness in target cells.is a member of the glycoprotein hormone family that includes follicle-stimulating hormone (FSH) and thyroid-stimulating hormone (1, 2). These hormones are heterodimers consisting of a common ␣-subunit noncovalently linked to a hormone-specific ␤-subunit. LH binds to G-protein coupled receptors on Leydig cells in the testis and granulosa and theca cells in the ovary (1, 2). During pubertal and postpubertal gonad development, LH promotes steroidogenesis required for normal reproductive function (1, 2). Less clear are its functions during embryonic gonad development, although evidence suggests that early gonad development is independent of gonadotropin stimulation (3, 4).Intercellular communication within the testis is essential for normal spermatogenesis (5, 6). In response to FSH, the Sertoli cells secrete various factors that affect Leydig cell function (7,8). Similarly, testosterone produced from Leydig cells is required for spermatogenesis (7,8). In females, ovarian folliculogenesis and ovulation are critically dependent on synchronized activities of both FSH and LH (9, 10). Previously, we and others have used genetic models, including FSH␤, FSH-receptor, and LHreceptor knockout mice, to study the physiological roles of gonadotropins in gonad developmen...

Chronic kidney disease (CKD) accelerates muscle protein degradation by stimulating the ubiquitin proteasome system through activation of the E3 ligases, Atrogin-1/MaFbx and MuRF-1. Forkhead transcription factors (FoxO) can control the expression of these E3 ligases, but the contribution of individual FoxOs to muscle wasting is unclear. To study this we created mice with a muscle-specific FoxO1 deletion. The absence of FoxO1 blocked 70% of the increase in E3 ligases induction by CKD as well as the proteolysis and loss of muscle mass. Thus, FoxO1 has a role in controlling ubiquitin proteasome system-related proteolysis. Since microRNA (miR)-486 reportedly dampens FoxO1 expression and its activity, we transfected a miR-486 mimic into primary cultures of myotubes and found this blocked dexamethasone-stimulated protein degradation without influencing protein synthesis. It also decreased FoxO1 protein translation and increased FoxO1 phosphorylation by down-regulation of PTEN phosphatase, a negative regulator of p-Akt. To test its efficacy in vivo, we electroporated miR-486 into muscles and found expression of the E3 ligases was suppressed and muscle mass increased despite CKD. Thus, FoxO1 is a dominant mediator of CKD-induced muscle wasting and miR-486 coordinately decreases FoxO1 and PTEN to protect against this catabolic response.

SUMMARY Tobacco smoking is a well-known risk factor for subsequent alcohol abuse, but the neural events underlying this risk remain largely unknown. Alcohol and nicotine reinforcement involve common neural circuitry, including the mesolimbic dopamine system. We demonstrate in rodents that pre-exposure to nicotine increases alcohol self-administration and decreases alcohol-induced dopamine responses. The blunted dopamine response was due to increased inhibitory synaptic transmission onto dopamine neurons. Blocking stress hormone receptors prior to nicotine exposure prevented all interactions with alcohol that we measured, including the increased inhibition onto dopamine neurons, the decreased dopamine responses, and the increased alcohol self-administration. These results indicate that nicotine recruits neuroendocrine systems to influence neurotransmission and behavior associated with alcohol reinforcement.