Polarization Second Harmonic (PSH) detects ultrastructural changes of collagen in different pathological conditions and enables to compute helical pitch angle (HPA) of PSH active structures arranged in fibers. Calculation of HPA is valid for cardiac thick filaments (CTF) in which myosin heavy chain (MHC) is the primary PSH active structure. We studied HPA of CTF in rats and rabbits to understand whether it is possible to correlate HPA with biological processes like aging and distribution of beta-MHC isoform.Methods
14 New Zealand Rabbits were sacrified at different ages: P0, P14, P70 and P365 and 6 animals with known distributions of beta-MHC (RatP56:10%, RabbitP14:50%, RabbitP365:95%) were used to prepare left ventricular tissue sections. PSH images were acquired in a modified inverted microscope to inject ultrashort laser pulses and polarization control. Each heart section was acquired at ten random locations of the left ventricle (LV). Eight different polarizations were captured per location and HPA was computed according to standard biophysical model. The HPA of an animal was computed as the average within all the acquired images. Pearson correlation was computed between HPA values and beta-MHC and the fourth root of days after birth.Results
HPA and days after birth resulted in a significant correlation of 0.76 and p=0.0016 (Fig.1a). HPA and beta-MHC distribution resulted in a significant correlation of 0.98 and p=0.0009 (Fig.1b).Conclusions
HPA integrates relevant information of the molecular architecture of CTF that correlates consistently with aging process of cardiac LV in rabbits and beta-MHC distribution. HPA can be an important imaging tool to study cardiac pathologies related to aging, development and beta-MHC changes.