Sex- and strain-differential plasma proteomic signatures in C57BL/6 and BALB/c mice

Sex is a critical determinant of health and disease, yet it remains underrepresented in biomedical research. The identification of blood-based biomarkers facilitates early diagnosis and intervention for various diseases; however, sex-differential differences in the plasma proteome have not been sufficiently explored in mouse models. Understanding the molecular features associated with sex is essential for enhancing the translational potential of clinical research. We utilized Olink technology to analyze sex- and strain-differential plasma protein expression in two widely used mouse strains, C57BL/6 and BALB/c. A total of 36 mice (n = 9 per strain and sex) were analyzed using the 'Olink Target 48 Mouse Cytokine' and 'Olink Target 96 Mouse Exploratory' panels. Differences in normalized protein expression (NPX) were compared between groups, and proteins with a P-value < 0.05 were considered significantly different. Our analysis identified 55 strain-differential proteins and 33 sex-differential proteins among the 87 proteins analyzed in mouse plasma. Importantly, LPL (Lipoprotein lipase) and GHRL (Appetite-regulating hormone) were also more highly expressed in females in human datasets, suggesting a conserved sex-biased expression pattern across species. This study characterized sex- and strain-differential differences in the plasma proteomes of C57BL/6 and BALB/c mice. Among the identified proteins, LPL and GHRL were significantly elevated in females, consistent with human gene and plasma protein expression trends. These findings highlight the presence of sex-based molecular differences in energy and lipid metabolism and provide a valuable foundation for future mechanistic studies.