## 1 Introduction  
Osteoarthritis affects people worldwide, especially those in advanced age. Currently, the global prevalence of knee OA is 3.7% of the population, which means 268 million people are suffering from OA in this particular joint [1]. However, OA can occur in any joints including hip, fingers, hands, wrist, and temporomandibular joints [2]; thus, the total prevalence of OA is greater than the previous estimation. The United Nations and World Health Organization placed this burden as the fourth leading cause of disability in 2020 [3]. The disease is characterized by articular cartilage deterioration, which progresses slowly and appears initially at a subclinical level, making it difficult to be detected at an early stage [4]. Therefore, patients diagnosed with OA already have some severity of cartilage erosion. Treatment is also challenged by the fact that avascular tissue such as cartilage has less ability to regenerate itself [5]. Moreover, microstructural damage to subchondral bone is replaced by fibrous tissue resulting in less porosity of subchondral bone plate, which limits the nutrient supply to the cartilage layers [6; 7]. The ideal strategies to alleviate the disease burden would focus on both prevention and halting disease progression rather than relieving pain by anti-inflammatory drugs. Effective treatments need to target the underlying causes of diseases but the etiology of OA is very complicated, especially in the case of metabolic osteoarthritis (MetOA). It is not clear whether OA is a single disease itself or a nebula of several diseases which have no specific markers to identify them. There are many animal models to study OA, including both spontaneous OA and induction OA models. The spontaneous OA model, using animals which are genetically prone to develop OA in advancing age [8; 9], theoretically mimics the pathological mechanisms for age-related OA in humans, whereas surgical induction OA models mimic post-traumatic OA [10]. The incidence of MetOA has been increasing due to the global expansion of obesity and related chronic diseases [11; 12], increasing the importance of developing and optimizing a reliable animal model for this OA phenotype. The use of a high energy diet due to increased fat or sugar proportion successfully induces obesity in rat models; however, the effectiveness of this model to generate OA is controversial. Some studies have revealed that high-fat alone was inadequate to cause cartilage lesions in a rodent model unless groove surgery was incorporated [13; 14]. However, other studies demonstrated that the pathological lesions of MetOA were successfully established in rats by feeding a high-fat diet for 16 or 28 weeks [15; 16; 17]. The success of these studies might be related to the gender as male rats are prone to osteoarthritis because of the influence of testosterone while female rats had become prone to the disease only when they lack estrogen [18]. In addition, the variation in success rates also depends on the type and quantity of fat [19]. It therefore remains inconclusive whether OA is inducible in female rats by a high energy diet or ovariectomy. This study focused on the MetOA in a female population, which is both the most prevalent phenotype and the most complicated. There is no established set of biomarkers to distinguish the phenotype or subtypes of OA. We hypothesized that different causes could activate MetOA in unique pathways resulting in distinguishable pathological patterns. Therefore, the experiment was designed to find the differences in pathological markers from individual causes and as well as additive causes.