The cost of lamb mortality caused by cold exposure has been estimated at approximately 40 million dollars per year. This value is probably conservative as it does not include the cost due to the reduction in productivity in hypothermic lambs that manage to survive or the cost of reduced selection potential incurred by fewer lambs surviving until selection. The objectives of this research was to investigate whether sire-line variation exists in neonatal lamb cold tolerance and whether polymorphism in the β₃ adrenergic receptor gene can be used as a genetic marker for lamb cold tolerance and lean muscle growth. The influence of the climate, birthweight, age of dam at lambing, gender and birth rank on neonatal lamb cold tolerance was also analysed. Neonatal lamb mortality due to cold exposure was analysed in four field trials that used neonatal lamb morality from cold exposure as a predictor of neonatal lamb cold tolerance. Sire-line variation in neonatal lamb morality was observed in all trials, though it appeared that this effect was largely mediated through sire-line variation in lamb birth weight. Variation in lamb birth weight between birth rank classed was also found to be responsible for the influence of birth rank on neonatal lamb mortality due to cold exposure. The age of dam at lambing and the lamb gender was not observed to influence neonatal lamb mortality due to cold exposure. The sires from the cold tolerance study and the progeny of the lean muscle growth study were genotyped for the β₃ adrenergic receptor locus. Other studies have found evidence that a major gene exists in the catecholamine stimulation of brown adipose thermogenesis and evidence that the β₃-AR gene is a likely candidate. However, this hypothesis and the hypothesis that polymorphism in the β₃-AR gene is also linked to lean muscle growth in lambs was not confirmed in this study. So while it appears that the results were confounded by experimental design, there is evidence that influence of polymorphism in the ovine β₃ AR gene on neonatal lamb mortality and/or lean muscle growth is not sufficient to be considered a major gene effect. The implications of this experiment on the sheep industry and sheep farmers in general are huge. While completely eliminating lamb deaths due to inadequate cold tolerance is impossible, this study shows that large gains in lamb survival could be possible through selective breeding.

Abstract The β1-adrenergic receptor (β1AR) belongs to the large family of G protein-coupled receptors. It is activated by epinephrine and norepinephrine and thus has a central role in mediating the effects of the sympathetic nervous system. β1AR is the predominant adrenergic receptor in the heart, where it mediates positive inotropy and chronotropy. Thus, it is the most important target receptor for β-adrenergic antagonists, which are widely used in the treatment of cardiovascular diseases. Furthermore, β1AR is also expressed in the brain, where it has a crucial role in regulating memory formation and synaptic plasticity. Human β1AR (hβ1AR) has two polymorphisms, one at each terminus. The carboxyl-terminal (C-terminal) Arg389Gly8.56 polymorphism has previously been shown to have functional significance. Despite the clinical importance of hβ1AR, its biosynthetic profile and post-translational processing have not been well characterized to date. The aims of the present study were to shed light on these events, focusing on the limited proteolysis of hβ1AR and the impact of β-adrenergic ligands on receptor processing. In addition, the C-terminal polymorphism and its associations with certain parameters were investigated in a population consisting of survivors of acute myocardial infarction (AMI). By using a heterologous expression system, hβ1AR biosynthesis was revealed to be efficient and rapid. The N-terminus of the mature receptor was modified with O-glycans and one N-glycan, but despite these modifications it was subject to cleavage at the cell surface that resulted in two C-terminal fragments. The cleavage was mediated by a metalloproteinase, and importantly, it also occurred in vivo. Moreover, receptor activation enhanced the cleavage, which suggests that it represents a novel regulatory mechanism of hβ1AR. Interestingly, those ligands that enhanced the cleavage stabilized intracellular hβ1AR precursors, possibly via a pharmacological chaperone activity. Thus, the present study demonstrates that β-adrenergic ligands can have different regulatory effects on distinct hβ1AR forms. Among the AMI survivors, the Arg3898.56 homozygotes had significantly increased left ventricular mass indexes, when compared to the Gly3898.56 carriers, which suggests an association between Arg3898.56 and left ventricular hypertrophy (LVH). When euglycemic and diabetic patients were analyzed separately, the association existed among the euglycemic patients but was not present in diabetic patients. Diabetes is one of several risk factors that have previously been shown to influence the progression of LVH. Here, diabetes was shown to have a stronger effect on the development of LVH, when compared with the Arg3898.56 variant of hβ1AR. / Tiivistelmä β1-adrenerginen reseptori (β1AR) kuuluu laajaan G-proteiineihin kytkettyjen reseptorien perheeseen. β1AR on tärkeässä asemassa sympaattisen hermoston toiminnassa. Sydämessä β1AR on vallitseva adrenerginen reseptori, ja sydänlihaksen supistusvireys sekä -taajuus voimistuvat β1AR:n aktivaation kautta. Siten se edustaa sydän- ja verisuonisairauksissa käytettävien β-salpaajien tärkeintä kohdereseptoria. β1AR:n luontaisia agonisteja ovat lisämunuaisytimestä ja hermopäätteistä vapautuvat adrenaliini ja noradrenaliini. Sydänlihaksen lisäksi β1AR:a ilmennetään myös aivoissa, jossa reseptorilla on keskeinen asema muistin ja synaptisen muovautuvuuden kannalta. Ihmisen β1AR (hβ1AR) sisältää kaksi polymorfismia, joista toinen (Arg389Gly8.56) sijaitsee reseptorin karboksyyli- (C-) terminaalissa solulimassa. Tällä polymorfismilla on havaittu olevan toiminnallista merkitystä. Vaikka hβ1AR:n kliininen merkitys on huomattava, sen biosynteesistä ja translaationjälkeisestä muokkauksesta ei ole tähän mennessä ollut juurikaan tutkimustietoa. Tämän väitöskirjatyön tavoite oli kuvata näitä tapahtumia ja erityisesti keskittyä hβ1AR:n solunulkoisen amino- (N-) terminaalin rajoitettuun proteolyysiin. Lisäksi haluttiin tutkia, onko β-adrenergisillä ligandeilla vaikutusta reseptorin prosessointiin. Tutkimuksen kliinisessä osiossa kartoitettiin C-terminaalisen polymorfian yhteyttä valikoituihin muuttujiin aineistossa, joka koostui akuutin sydäninfarktin (AMI) sairastaneista potilaista. hβ1AR:n biosynteesin havaittiin olevan tehokas ja nopea heterologisessa systeemissä. Kypsän reseptorin N-terminaalissa havaittiin useita O-kytkennäisiä ja yksi N-kytkennäinen glykaani. Glykosyloinnista huolimatta N-terminaali pilkkoutui solun pinnalla, mikä tuotti kaksi solukalvolla sijaitsevaa, C-terminaalista reseptoripalasta. Pilkkoutumista, joka havaittiin myös in vivo, katalysoi metalloproteinaasi. Reseptorin aktivaatio kiihdytti pilkkoutumista, joka siten todennäköisesti edustaa uudenlaista hβ1AR:n säätelymekanismia. Ligandit, jotka kiihdyttivät pilkkoutumista, toisaalta stabiloivat solunsisäisiä hβ1AR:n epäkypsiä muotoja toimien luultavasti ns. farmakologisina kaperoneina. Näin ollen väitöskirjatyö osoittaa, että β-adrenergisillä ligandeilla voi olla erilaisia säätelyvaikutuksia eri hβ1AR-muotoihin. Kliinisessä tutkimuksessa Arg3898.56-homotsygooteilla potilailla havaittiin merkittävästi suurentunut vasemman kammion massaindeksi Gly3898.56-kantajiin verrattuina, mikä puoltaa Arg3898.56-polymorfismin ja vasemman kammion hypertrofian (LVH) välistä yhteyttä. Kun euglykeemisiä potilaita ja diabeetikkoja tutkittiin erikseen, yhteys ilmeni vain euglykeemisessä ryhmässä. Diabetes on riskitekijä, joka vaikuttaa LVH:n kehittymiseen. Tässä tutkimuksessa diabeteksellä havaittiin olevan voimakkaampi vaikutus LVH:n kehittymiseen Arg3898.56 -polymorfismiin verrattuna.